[ty] handle recursive type inference properly (#20566)

## Summary

Derived from #17371

Fixes astral-sh/ty#256
Fixes https://github.com/astral-sh/ty/issues/1415
Fixes https://github.com/astral-sh/ty/issues/1433
Fixes https://github.com/astral-sh/ty/issues/1524

Properly handles any kind of recursive inference and prevents panics.

---

Let me explain techniques for converging fixed-point iterations during
recursive type inference.
There are two types of type inference that naively don't converge
(causing salsa to panic): divergent type inference and oscillating type
inference.

### Divergent type inference

Divergent type inference occurs when eagerly expanding a recursive type.
A typical example is this:

```python
class C:
    def f(self, other: "C"):
        self.x = (other.x, 1)

reveal_type(C().x) # revealed: Unknown | tuple[Unknown | tuple[Unknown | tuple[..., Literal[1]], Literal[1]], Literal[1]]
```

To solve this problem, we have already introduced `Divergent` types
(https://github.com/astral-sh/ruff/pull/20312). `Divergent` types are
treated as a kind of dynamic type [^1].

```python
Unknown | tuple[Unknown | tuple[Unknown | tuple[..., Literal[1]], Literal[1]], Literal[1]]
=> Unknown | tuple[Divergent, Literal[1]]
```

When a query function that returns a type enters a cycle, it sets
`Divergent` as the cycle initial value (instead of `Never`). Then, in
the cycle recovery function, it reduces the nesting of types containing
`Divergent` to converge.

```python
0th: Divergent
1st: Unknown | tuple[Divergent, Literal[1]]
2nd: Unknown | tuple[Unknown | tuple[Divergent, Literal[1]], Literal[1]]
=> Unknown | tuple[Divergent, Literal[1]]
```

Each cycle recovery function for each query should operate only on the
`Divergent` type originating from that query.
For this reason, while `Divergent` appears the same as `Any` to the
user, it internally carries some information: the location where the
cycle occurred. Previously, we roughly identified this by having the
scope where the cycle occurred, but with the update to salsa, functions
that create cycle initial values ​​can now receive a `salsa::Id`
(https://github.com/salsa-rs/salsa/pull/1012). This is an opaque ID that
uniquely identifies the cycle head (the query that is the starting point
for the fixed-point iteration). `Divergent` now has this `salsa::Id`.

### Oscillating type inference

Now, another thing to consider is oscillating type inference.
Oscillating type inference arises from the fact that monotonicity is
broken. Monotonicity here means that for a query function, if it enters
a cycle, the calculation must start from a "bottom value" and progress
towards the final result with each cycle. Monotonicity breaks down in
type systems that have features like overloading and overriding.

```python
class Base:
    def flip(self) -> "Sub":
        return Sub()

class Sub(Base):
    def flip(self) -> "Base":
        return Base()

class C:
    def __init__(self, x: Sub):
        self.x = x

    def replace_with(self, other: "C"):
        self.x = other.x.flip()

reveal_type(C(Sub()).x)
```

Naive fixed-point iteration results in `Divergent -> Sub -> Base -> Sub
-> ...`, which oscillates forever without diverging or converging. To
address this, the salsa API has been modified so that the cycle recovery
function receives the value of the previous cycle
(https://github.com/salsa-rs/salsa/pull/1012).
The cycle recovery function returns the union type of the current cycle
and the previous cycle. In the above example, the result type for each
cycle is `Divergent -> Sub -> Base (= Sub | Base) -> Base`, which
converges.

The final result of oscillating type inference does not contain
`Divergent` because `Divergent` that appears in a union type can be
removed, as is clear from the expansion. This simplification is
performed at the same time as nesting reduction.

```
T | Divergent = T | (T | (T | ...)) = T
```

[^1]: In theory, it may be possible to strictly treat types containing
`Divergent` types as recursive types, but we probably shouldn't go that
deep yet. (AFAIK, there are no PEPs that specify how to handle
implicitly recursive types that aren't named by type aliases)

## Performance analysis

A happy side effect of this PR is that we've observed widespread
performance improvements!
This is likely due to the removal of the `ITERATIONS_BEFORE_FALLBACK`
and max-specialization depth trick
(https://github.com/astral-sh/ty/issues/1433,
https://github.com/astral-sh/ty/issues/1415), which means we reach a
fixed point much sooner.

## Ecosystem analysis

The changes look good overall.
You may notice changes in the converged values ​​for recursive types,
this is because the way recursive types are normalized has been changed.
Previously, types containing `Divergent` types were normalized by
replacing them with the `Divergent` type itself, but in this PR, types
with a nesting level of 2 or more that contain `Divergent` types are
normalized by replacing them with a type with a nesting level of 1. This
means that information about the non-divergent parts of recursive types
is no longer lost.

```python
# previous
tuple[tuple[Divergent, int], int] => Divergent
# now
tuple[tuple[Divergent, int], int] => tuple[Divergent, int]
```

The false positive error introduced in this PR occurs in class
definitions with self-referential base classes, such as the one below.

```python
from typing_extensions import Generic, TypeVar

T = TypeVar("T")
U = TypeVar("U")

class Base2(Generic[T, U]): ...

# TODO: no error
# error: [unsupported-base] "Unsupported class base with type `<class 'Base2[Sub2, U@Sub2]'> | <class 'Base2[Sub2[Unknown], U@Sub2]'>`"
class Sub2(Base2["Sub2", U]): ...
```

This is due to the lack of support for unions of MROs, or because cyclic
legacy generic types are not inferred as generic types early in the
query cycle.

## Test Plan

All samples listed in astral-sh/ty#256 are tested and passed without any
panic!

## Acknowledgments

Thanks to @MichaReiser for working on bug fixes and improvements to
salsa for this PR. @carljm also contributed early on to the discussion
of the query convergence mechanism proposed in this PR.

---------

Co-authored-by: Carl Meyer <carl@astral.sh>

crates/ty/docs/rules.md

@@ -39,7 +39,7 @@ def test(): -> "int":
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20call-non-callable" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L130" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L131" target="_blank">View source</a>
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@@ -63,7 +63,7 @@ Calling a non-callable object will raise a `TypeError` at runtime.
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@@ -95,7 +95,7 @@ f(int)  # error
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L200" target="_blank">View source</a>
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@@ -126,7 +126,7 @@ a = 1
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 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L225" target="_blank">View source</a>
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@@ -158,7 +158,7 @@ class C(A, B): ...
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L252" target="_blank">View source</a>
 </small>
 
 
@@ -184,13 +184,41 @@ class B(A): ...
 
 [method resolution order]: https://docs.python.org/3/glossary.html#term-method-resolution-order
 
+## `cyclic-type-alias-definition`
+
+<small>
+Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
+Preview (since <a href="https://github.com/astral-sh/ty/releases/tag/1.0.0">1.0.0</a>) ·
+<a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20cyclic-type-alias-definition" target="_blank">Related issues</a> ·
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L278" target="_blank">View source</a>
+</small>
+
+
+**What it does**
+
+Checks for type alias definitions that (directly or mutually) refer to themselves.
+
+**Why is it bad?**
+
+Although it is permitted to define a recursive type alias, it is not meaningful
+to have a type alias whose expansion can only result in itself, and is therefore not allowed.
+
+**Examples**
+
+```python
+type Itself = Itself
+
+type A = B
+type B = A
+```
+
 ## `duplicate-base`
 
 <small>
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
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@@ -217,7 +245,7 @@ class B(A, A): ...
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 </small>
 
 
@@ -329,7 +357,7 @@ def test(): -> "Literal[5]":
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L564" target="_blank">View source</a>
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@@ -359,7 +387,7 @@ class C(A, B): ...
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L565" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L588" target="_blank">View source</a>
 </small>
 
 
@@ -385,7 +413,7 @@ t[3]  # IndexError: tuple index out of range
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 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.12">0.0.1-alpha.12</a> ·
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L369" target="_blank">View source</a>
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@@ -474,7 +502,7 @@ an atypical memory layout.
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
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+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L642" target="_blank">View source</a>
 </small>
 
 
@@ -501,7 +529,7 @@ func("foo")  # error: [invalid-argument-type]
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L659" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L682" target="_blank">View source</a>
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@@ -529,7 +557,7 @@ a: int = ''
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1877" target="_blank">View source</a>
 </small>
 
 
@@ -563,7 +591,7 @@ C.instance_var = 3  # error: Cannot assign to instance variable
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.19">0.0.1-alpha.19</a> ·
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L681" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L704" target="_blank">View source</a>
 </small>
 
 
@@ -599,7 +627,7 @@ asyncio.run(main())
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L711" target="_blank">View source</a>
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@@ -623,7 +651,7 @@ class A(42): ...  # error: [invalid-base]
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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@@ -650,7 +678,7 @@ with 1:
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
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 </small>
 
 
@@ -679,7 +707,7 @@ a: str
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
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-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L806" target="_blank">View source</a>
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 </small>
 
 
@@ -723,7 +751,7 @@ except ZeroDivisionError:
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
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 </small>
 
 
@@ -765,7 +793,7 @@ class D(A):
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-generic-class" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L842" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L865" target="_blank">View source</a>
 </small>
 
 
@@ -798,7 +826,7 @@ class C[U](Generic[T]): ...
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.17">0.0.1-alpha.17</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-key" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L586" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L609" target="_blank">View source</a>
 </small>
 
 
@@ -837,7 +865,7 @@ carol = Person(name="Carol", age=25)  # typo!
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-legacy-type-variable" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L868" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L891" target="_blank">View source</a>
 </small>
 
 
@@ -872,7 +900,7 @@ def f(t: TypeVar("U")): ...
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-metaclass" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L965" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L988" target="_blank">View source</a>
 </small>
 
 
@@ -906,7 +934,7 @@ class B(metaclass=f): ...
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.20">0.0.1-alpha.20</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-method-override" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1982" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L2005" target="_blank">View source</a>
 </small>
 
 
@@ -992,7 +1020,7 @@ and `__ne__` methods accept `object` as their second argument.
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.19">0.0.1-alpha.19</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-named-tuple" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L515" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L538" target="_blank">View source</a>
 </small>
 
 
@@ -1024,7 +1052,7 @@ TypeError: can only inherit from a NamedTuple type and Generic
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Preview (since <a href="https://github.com/astral-sh/ty/releases/tag/1.0.0">1.0.0</a>) ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-newtype" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L941" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L964" target="_blank">View source</a>
 </small>
 
 
@@ -1054,7 +1082,7 @@ Baz = NewType("Baz", int | str)  # error: invalid base for `typing.NewType`
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-overload" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L992" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1015" target="_blank">View source</a>
 </small>
 
 
@@ -1104,7 +1132,7 @@ def foo(x: int) -> int: ...
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-parameter-default" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1091" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1114" target="_blank">View source</a>
 </small>
 
 
@@ -1130,7 +1158,7 @@ def f(a: int = ''): ...
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-paramspec" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L896" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L919" target="_blank">View source</a>
 </small>
 
 
@@ -1161,7 +1189,7 @@ P2 = ParamSpec("S2")  # error: ParamSpec name must match the variable it's assig
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-protocol" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L451" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L474" target="_blank">View source</a>
 </small>
 
 
@@ -1195,7 +1223,7 @@ TypeError: Protocols can only inherit from other protocols, got <class 'int'>
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-raise" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1111" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1134" target="_blank">View source</a>
 </small>
 
 
@@ -1244,7 +1272,7 @@ def g():
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-return-type" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L640" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L663" target="_blank">View source</a>
 </small>
 
 
@@ -1269,7 +1297,7 @@ def func() -> int:
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-super-argument" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1154" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1177" target="_blank">View source</a>
 </small>
 
 
@@ -1327,7 +1355,7 @@ TODO #14889
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.6">0.0.1-alpha.6</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-alias-type" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L920" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L943" target="_blank">View source</a>
 </small>
 
 
@@ -1354,7 +1382,7 @@ NewAlias = TypeAliasType(get_name(), int)        # error: TypeAliasType name mus
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-checking-constant" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1193" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1216" target="_blank">View source</a>
 </small>
 
 
@@ -1384,7 +1412,7 @@ TYPE_CHECKING = ''
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-form" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1217" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1240" target="_blank">View source</a>
 </small>
 
 
@@ -1414,7 +1442,7 @@ b: Annotated[int]  # `Annotated` expects at least two arguments
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.11">0.0.1-alpha.11</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-guard-call" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1269" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1292" target="_blank">View source</a>
 </small>
 
 
@@ -1448,7 +1476,7 @@ f(10)  # Error
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.11">0.0.1-alpha.11</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-guard-definition" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1241" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1264" target="_blank">View source</a>
 </small>
 
 
@@ -1482,7 +1510,7 @@ class C:
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20invalid-type-variable-constraints" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1297" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1320" target="_blank">View source</a>
 </small>
 
 
@@ -1517,7 +1545,7 @@ T = TypeVar('T', bound=str)  # valid bound TypeVar
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20missing-argument" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1326" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1349" target="_blank">View source</a>
 </small>
 
 
@@ -1542,7 +1570,7 @@ func()  # TypeError: func() missing 1 required positional argument: 'x'
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.20">0.0.1-alpha.20</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20missing-typed-dict-key" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1955" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1978" target="_blank">View source</a>
 </small>
 
 
@@ -1575,7 +1603,7 @@ alice["age"]  # KeyError
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20no-matching-overload" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1345" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1368" target="_blank">View source</a>
 </small>
 
 
@@ -1604,7 +1632,7 @@ func("string")  # error: [no-matching-overload]
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20non-subscriptable" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1368" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1391" target="_blank">View source</a>
 </small>
 
 
@@ -1628,7 +1656,7 @@ Subscripting an object that does not support it will raise a `TypeError` at runt
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20not-iterable" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1386" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1409" target="_blank">View source</a>
 </small>
 
 
@@ -1654,7 +1682,7 @@ for i in 34:  # TypeError: 'int' object is not iterable
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20parameter-already-assigned" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1437" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1460" target="_blank">View source</a>
 </small>
 
 
@@ -1681,7 +1709,7 @@ f(1, x=2)  # Error raised here
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.22">0.0.1-alpha.22</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20positional-only-parameter-as-kwarg" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1708" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1731" target="_blank">View source</a>
 </small>
 
 
@@ -1739,7 +1767,7 @@ def test(): -> "int":
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20static-assert-error" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1830" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1853" target="_blank">View source</a>
 </small>
 
 
@@ -1769,7 +1797,7 @@ static_assert(int(2.0 * 3.0) == 6)  # error: does not have a statically known tr
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20subclass-of-final-class" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1528" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1551" target="_blank">View source</a>
 </small>
 
 
@@ -1798,7 +1826,7 @@ class B(A): ...  # Error raised here
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20too-many-positional-arguments" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1609" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1632" target="_blank">View source</a>
 </small>
 
 
@@ -1825,7 +1853,7 @@ f("foo")  # Error raised here
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20type-assertion-failure" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1587" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1610" target="_blank">View source</a>
 </small>
 
 
@@ -1853,7 +1881,7 @@ def _(x: int):
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unavailable-implicit-super-arguments" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1630" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1653" target="_blank">View source</a>
 </small>
 
 
@@ -1899,7 +1927,7 @@ class A:
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unknown-argument" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1687" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1710" target="_blank">View source</a>
 </small>
 
 
@@ -1926,7 +1954,7 @@ f(x=1, y=2)  # Error raised here
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unresolved-attribute" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1729" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1752" target="_blank">View source</a>
 </small>
 
 
@@ -1954,7 +1982,7 @@ A().foo  # AttributeError: 'A' object has no attribute 'foo'
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unresolved-import" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1751" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1774" target="_blank">View source</a>
 </small>
 
 
@@ -1979,7 +2007,7 @@ import foo  # ModuleNotFoundError: No module named 'foo'
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unresolved-reference" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1770" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1793" target="_blank">View source</a>
 </small>
 
 
@@ -2004,7 +2032,7 @@ print(x)  # NameError: name 'x' is not defined
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unsupported-bool-conversion" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1406" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1429" target="_blank">View source</a>
 </small>
 
 
@@ -2041,7 +2069,7 @@ b1 < b2 < b1  # exception raised here
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unsupported-operator" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1789" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1812" target="_blank">View source</a>
 </small>
 
 
@@ -2069,7 +2097,7 @@ A() + A()  # TypeError: unsupported operand type(s) for +: 'A' and 'A'
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'error'."><code>error</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20zero-stepsize-in-slice" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1811" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1834" target="_blank">View source</a>
 </small>
 
 
@@ -2094,7 +2122,7 @@ l[1:10:0]  # ValueError: slice step cannot be zero
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.20">0.0.1-alpha.20</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20ambiguous-protocol-member" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L480" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L503" target="_blank">View source</a>
 </small>
 
 
@@ -2135,7 +2163,7 @@ class SubProto(BaseProto, Protocol):
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.16">0.0.1-alpha.16</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20deprecated" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L295" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L318" target="_blank">View source</a>
 </small>
 
 
@@ -2223,7 +2251,7 @@ a = 20 / 0  # type: ignore
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.22">0.0.1-alpha.22</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-missing-attribute" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1458" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1481" target="_blank">View source</a>
 </small>
 
 
@@ -2251,7 +2279,7 @@ A.c  # AttributeError: type object 'A' has no attribute 'c'
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.22">0.0.1-alpha.22</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-missing-implicit-call" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L148" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L149" target="_blank">View source</a>
 </small>
 
 
@@ -2283,7 +2311,7 @@ A()[0]  # TypeError: 'A' object is not subscriptable
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.22">0.0.1-alpha.22</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-missing-import" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1480" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1503" target="_blank">View source</a>
 </small>
 
 
@@ -2315,7 +2343,7 @@ from module import a  # ImportError: cannot import name 'a' from 'module'
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20redundant-cast" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1882" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1905" target="_blank">View source</a>
 </small>
 
 
@@ -2342,7 +2370,7 @@ cast(int, f())  # Redundant
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20undefined-reveal" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1669" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1692" target="_blank">View source</a>
 </small>
 
 
@@ -2366,7 +2394,7 @@ reveal_type(1)  # NameError: name 'reveal_type' is not defined
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.15">0.0.1-alpha.15</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unresolved-global" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1903" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1926" target="_blank">View source</a>
 </small>
 
 
@@ -2424,7 +2452,7 @@ def g():
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.7">0.0.1-alpha.7</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20unsupported-base" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L729" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L752" target="_blank">View source</a>
 </small>
 
 
@@ -2463,7 +2491,7 @@ class D(C): ...  # error: [unsupported-base]
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'warn'."><code>warn</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.22">0.0.1-alpha.22</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20useless-overload-body" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1035" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1058" target="_blank">View source</a>
 </small>
 
 
@@ -2526,7 +2554,7 @@ def foo(x: int | str) -> int | str:
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'ignore'."><code>ignore</code></a> ·
 Preview (since <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a>) ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20division-by-zero" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L277" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L300" target="_blank">View source</a>
 </small>
 
 
@@ -2550,7 +2578,7 @@ Dividing by zero raises a `ZeroDivisionError` at runtime.
 Default level: <a href="../rules.md#rule-levels" title="This lint has a default level of 'ignore'."><code>ignore</code></a> ·
 Added in <a href="https://github.com/astral-sh/ty/releases/tag/0.0.1-alpha.1">0.0.1-alpha.1</a> ·
 <a href="https://github.com/astral-sh/ty/issues?q=sort%3Aupdated-desc%20is%3Aissue%20is%3Aopen%20possibly-unresolved-reference" target="_blank">Related issues</a> ·
-<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1506" target="_blank">View source</a>
+<a href="https://github.com/astral-sh/ruff/blob/main/crates%2Fty_python_semantic%2Fsrc%2Ftypes%2Fdiagnostic.rs#L1529" target="_blank">View source</a>
 </small>
 
 

crates/ty_python_semantic/resources/corpus/classliteral_decorators_cycle.py

@@ -0,0 +1,26 @@
+try:
+    type name_4 = name_1
+finally:
+    from .. import name_3
+
+try:
+    pass
+except* 0:
+    pass
+else:
+    def name_1() -> name_4:
+        pass
+
+    @name_1
+    def name_3():
+        pass
+finally:
+    try:
+        pass
+    except* 0:
+        assert name_3
+    finally:
+
+        @name_3
+        class name_1:
+            pass

crates/ty_python_semantic/resources/corpus/cyclic_reassignment.py

@@ -0,0 +1,5 @@
+class foo[_: foo](object): ...
+
+[_] = (foo,) = foo
+
+def foo(): ...

crates/ty_python_semantic/resources/corpus/cyclic_type_alias.py

@@ -0,0 +1,20 @@
+name_3: Foo = 0
+name_4 = 0
+
+if _0:
+    type name_3 = name_5
+    type name_4 = name_3
+
+_1: name_3
+
+def name_1(_2: name_4):
+    pass
+
+match 0:
+    case name_1._3:
+        pass
+    case 1:
+        type name_5 = name_4
+    case name_5:
+        pass
+name_3 = name_5

crates/ty_python_semantic/resources/mdtest/attributes.md

@@ -2383,6 +2383,34 @@ class B:
 
 reveal_type(B().x)  # revealed: Unknown | Literal[1]
 reveal_type(A().x)  # revealed: Unknown | Literal[1]
+
+class Base:
+    def flip(self) -> "Sub":
+        return Sub()
+
+class Sub(Base):
+    # error: [invalid-method-override]
+    def flip(self) -> "Base":
+        return Base()
+
+class C2:
+    def __init__(self, x: Sub):
+        self.x = x
+
+    def replace_with(self, other: "C2"):
+        self.x = other.x.flip()
+
+reveal_type(C2(Sub()).x)  # revealed: Unknown | Base
+
+class C3:
+    def __init__(self, x: Sub):
+        self.x = [x]
+
+    def replace_with(self, other: "C3"):
+        self.x = [self.x[0].flip()]
+
+# TODO: should be `Unknown | list[Unknown | Sub] | list[Unknown | Base]`
+reveal_type(C3(Sub()).x)  # revealed: Unknown | list[Unknown | Sub] | list[Divergent]
 ```
 
 And cycles between many attributes:
@@ -2432,6 +2460,30 @@ class ManyCycles:
         reveal_type(self.x5)  # revealed: Unknown | int
         reveal_type(self.x6)  # revealed: Unknown | int
         reveal_type(self.x7)  # revealed: Unknown | int
+
+class ManyCycles2:
+    def __init__(self: "ManyCycles2"):
+        self.x1 = [0]
+        self.x2 = [1]
+        self.x3 = [1]
+
+    def f1(self: "ManyCycles2"):
+        # TODO: should be Unknown | list[Unknown | int] | list[Divergent]
+        reveal_type(self.x3)  # revealed: Unknown | list[Unknown | int] | list[Divergent] | list[Divergent]
+
+        self.x1 = [self.x2] + [self.x3]
+        self.x2 = [self.x1] + [self.x3]
+        self.x3 = [self.x1] + [self.x2]
+
+    def f2(self: "ManyCycles2"):
+        self.x1 = self.x2 + self.x3
+        self.x2 = self.x1 + self.x3
+        self.x3 = self.x1 + self.x2
+
+    def f3(self: "ManyCycles2"):
+        self.x1 = self.x2 + self.x3
+        self.x2 = self.x1 + self.x3
+        self.x3 = self.x1 + self.x2
 ```
 
 This case additionally tests our union/intersection simplification logic:
@@ -2611,12 +2663,18 @@ reveal_type(Answer.__members__)  # revealed: MappingProxyType[str, Unknown]
 
 ## Divergent inferred implicit instance attribute types
 
+If an implicit attribute is defined recursively and type inference diverges, the divergent part is
+filled in with the dynamic type `Divergent`. Types containing `Divergent` can be seen as "cheap"
+recursive types: they are not true recursive types based on recursive type theory, so no unfolding
+is performed when you use them.
+
 ```py
 class C:
     def f(self, other: "C"):
         self.x = (other.x, 1)
 
 reveal_type(C().x)  # revealed: Unknown | tuple[Divergent, Literal[1]]
+reveal_type(C().x[0])  # revealed: Unknown | Divergent
 ```
 
 This also works if the tuple is not constructed directly:
@@ -2655,11 +2713,11 @@ And it also works for homogeneous tuples:
 def make_homogeneous_tuple(x: T) -> tuple[T, ...]:
     return (x, x)
 
-class E:
+class F:
-    def f(self, other: "E"):
+    def f(self, other: "F"):
         self.x = make_homogeneous_tuple(other.x)
 
-reveal_type(E().x)  # revealed: Unknown | tuple[Divergent, ...]
+reveal_type(F().x)  # revealed: Unknown | tuple[Divergent, ...]
 ```
 
 ## Attributes of standard library modules that aren't yet defined

crates/ty_python_semantic/resources/mdtest/cycle.md

@@ -32,6 +32,55 @@ reveal_type(p.x)  # revealed: Unknown | int
 reveal_type(p.y)  # revealed: Unknown | int
 ```
 
+## Self-referential bare type alias
+
+```toml
+[environment]
+python-version = "3.12"  # typing.TypeAliasType
+```
+
+```py
+from typing import Union, TypeAliasType, Sequence, Mapping
+
+A = list["A" | None]
+
+def f(x: A):
+    # TODO: should be `list[A | None]`?
+    reveal_type(x)  # revealed: list[Divergent]
+    # TODO: should be `A | None`?
+    reveal_type(x[0])  # revealed: Divergent
+
+JSONPrimitive = Union[str, int, float, bool, None]
+JSONValue = TypeAliasType("JSONValue", 'Union[JSONPrimitive, Sequence["JSONValue"], Mapping[str, "JSONValue"]]')
+```
+
+## Self-referential legacy type variables
+
+```py
+from typing import Generic, TypeVar
+
+B = TypeVar("B", bound="Base")
+
+class Base(Generic[B]):
+    pass
+
+T = TypeVar("T", bound="Foo[int]")
+
+class Foo(Generic[T]): ...
+```
+
+## Self-referential PEP-695 type variables
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+class Node[T: "Node[int]"]:
+    pass
+```
+
 ## Parameter default values
 
 This is a regression test for <https://github.com/astral-sh/ty/issues/1402>. When a parameter has a

crates/ty_python_semantic/resources/mdtest/generics/legacy/classes.md

@@ -732,6 +732,14 @@ class Base(Generic[T]): ...
 class Sub(Base["Sub"]): ...
 
 reveal_type(Sub)  # revealed: <class 'Sub'>
+
+U = TypeVar("U")
+
+class Base2(Generic[T, U]): ...
+
+# TODO: no error
+# error: [unsupported-base] "Unsupported class base with type `<class 'Base2[Sub2, U@Sub2]'> | <class 'Base2[Sub2[Unknown], U@Sub2]'>`"
+class Sub2(Base2["Sub2", U]): ...
 ```
 
 #### Without string forward references
@@ -756,6 +764,8 @@ from typing_extensions import Generic, TypeVar
 
 T = TypeVar("T")
 
+# TODO: no error "Unsupported class base with type `<class 'list[Derived[T@Derived]]'> | <class 'list[@Todo]'>`"
+# error: [unsupported-base]
 class Derived(list[Derived[T]], Generic[T]): ...
 ```
 

crates/ty_python_semantic/resources/mdtest/import/cyclic.md

@@ -38,7 +38,7 @@ See: <https://github.com/astral-sh/ty/issues/113>
 from pkg.sub import A
 
 # TODO: This should be `<class 'A'>`
-reveal_type(A)  # revealed: Never
+reveal_type(A)  # revealed: Divergent
 ```
 
 `pkg/outer.py`:

crates/ty_python_semantic/resources/mdtest/pep613_type_aliases.md

@@ -144,17 +144,46 @@ def _(x: IntOrStr):
 ## Cyclic
 
 ```py
-from typing import TypeAlias
+from typing import TypeAlias, TypeVar, Union
+from types import UnionType
 
 RecursiveTuple: TypeAlias = tuple[int | "RecursiveTuple", str]
 
 def _(rec: RecursiveTuple):
+    # TODO should be `tuple[int | RecursiveTuple, str]`
     reveal_type(rec)  # revealed: tuple[Divergent, str]
 
 RecursiveHomogeneousTuple: TypeAlias = tuple[int | "RecursiveHomogeneousTuple", ...]
 
 def _(rec: RecursiveHomogeneousTuple):
+    # TODO should be `tuple[int | RecursiveHomogeneousTuple, ...]`
     reveal_type(rec)  # revealed: tuple[Divergent, ...]
+
+ClassInfo: TypeAlias = type | UnionType | tuple["ClassInfo", ...]
+reveal_type(ClassInfo)  # revealed: types.UnionType
+
+def my_isinstance(obj: object, classinfo: ClassInfo) -> bool:
+    # TODO should be `type | UnionType | tuple[ClassInfo, ...]`
+    reveal_type(classinfo)  # revealed: type | UnionType | tuple[Divergent, ...]
+    return isinstance(obj, classinfo)
+
+K = TypeVar("K")
+V = TypeVar("V")
+NestedDict: TypeAlias = dict[K, Union[V, "NestedDict[K, V]"]]
+
+def _(nested: NestedDict[str, int]):
+    # TODO should be `dict[str, int | NestedDict[str, int]]`
+    reveal_type(nested)  # revealed: @Todo(specialized generic alias in type expression)
+
+my_isinstance(1, int)
+my_isinstance(1, int | str)
+my_isinstance(1, (int, str))
+my_isinstance(1, (int, (str, float)))
+my_isinstance(1, (int, (str | float)))
+# error: [invalid-argument-type]
+my_isinstance(1, 1)
+# TODO should be an invalid-argument-type error
+my_isinstance(1, (int, (str, 1)))
 ```
 
 ## Conditionally imported on Python < 3.10

crates/ty_python_semantic/resources/mdtest/pep695_type_aliases.md

@@ -106,6 +106,29 @@ def _(flag: bool):
 ```py
 type ListOrSet[T] = list[T] | set[T]
 reveal_type(ListOrSet.__type_params__)  # revealed: tuple[TypeVar | ParamSpec | TypeVarTuple, ...]
+type Tuple1[T] = tuple[T]
+
+def _(cond: bool):
+    Generic = ListOrSet if cond else Tuple1
+
+    def _(x: Generic[int]):
+        reveal_type(x)  # revealed: list[int] | set[int] | tuple[int]
+
+try:
+    class Foo[T]:
+        x: T
+        def foo(self) -> T:
+            return self.x
+
+    ...
+except Exception:
+    class Foo[T]:
+        x: T
+        def foo(self) -> T:
+            return self.x
+
+def f(x: Foo[int]):
+    reveal_type(x.foo())  # revealed: int
 ```
 
 ## In unions and intersections
@@ -244,6 +267,47 @@ def f(x: IntOr, y: OrInt):
         reveal_type(x)  # revealed: Never
     if not isinstance(y, int):
         reveal_type(y)  # revealed: Never
+
+# error: [cyclic-type-alias-definition] "Cyclic definition of `Itself`"
+type Itself = Itself
+
+def foo(
+    # this is a very strange thing to do, but this is a regression test to ensure it doesn't panic
+    Itself: Itself,
+):
+    x: Itself
+    reveal_type(Itself)  # revealed: Divergent
+
+# A type alias defined with invalid recursion behaves as a dynamic type.
+foo(42)
+foo("hello")
+
+# error: [cyclic-type-alias-definition] "Cyclic definition of `A`"
+type A = B
+# error: [cyclic-type-alias-definition] "Cyclic definition of `B`"
+type B = A
+
+def bar(B: B):
+    x: B
+    reveal_type(B)  # revealed: Divergent
+
+# error: [cyclic-type-alias-definition] "Cyclic definition of `G`"
+type G[T] = G[T]
+# error: [cyclic-type-alias-definition] "Cyclic definition of `H`"
+type H[T] = I[T]
+# error: [cyclic-type-alias-definition] "Cyclic definition of `I`"
+type I[T] = H[T]
+
+# It's not possible to create an element of this type, but it's not an error for now
+type DirectRecursiveList[T] = list[DirectRecursiveList[T]]
+
+# TODO: this should probably be a cyclic-type-alias-definition error
+type Foo[T] = list[T] | Bar[T]
+type Bar[T] = int | Foo[T]
+
+def _(x: Bar[int]):
+    # TODO: should be `int | list[int]`
+    reveal_type(x)  # revealed: int | list[int] | Any
 ```
 
 ### With legacy generic
@@ -327,7 +391,7 @@ class C(P[T]):
     pass
 
 reveal_type(C[int]())  # revealed: C[int]
-reveal_type(C())  # revealed: C[Divergent]
+reveal_type(C())  # revealed: C[C[Divergent]]
 ```
 
 ### Union inside generic

crates/ty_python_semantic/resources/mdtest/regression/1377_iteration_count_mismatch.md

@@ -2,10 +2,7 @@
 
 Regression test for <https://github.com/astral-sh/ty/issues/1377>.
 
-The code is an excerpt from <https://github.com/Gobot1234/steam.py> that is minimal enough to
+The code is an excerpt from <https://github.com/Gobot1234/steam.py>.
-trigger the iteration count mismatch bug in Salsa.
-
-<!-- expect-panic: execute: too many cycle iterations -->
 
 ```toml
 [environment]

crates/ty_python_semantic/src/place.rs

@@ -87,7 +87,7 @@ impl TypeOrigin {
 /// bound_or_declared:   Place::Defined(Literal[1], TypeOrigin::Inferred, Definedness::PossiblyUndefined),
 /// non_existent:        Place::Undefined,
 /// ```
-#[derive(Debug, Clone, PartialEq, Eq, salsa::Update, get_size2::GetSize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, salsa::Update, get_size2::GetSize)]
 pub(crate) enum Place<'db> {
     Defined(Type<'db>, TypeOrigin, Definedness),
     Undefined,
@@ -532,7 +532,7 @@ impl<'db> PlaceFromDeclarationsResult<'db> {
 /// that this comes with a [`CLASS_VAR`] type qualifier.
 ///
 /// [`CLASS_VAR`]: crate::types::TypeQualifiers::CLASS_VAR
-#[derive(Debug, Clone, PartialEq, Eq, salsa::Update, get_size2::GetSize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, salsa::Update, get_size2::GetSize)]
 pub(crate) struct PlaceAndQualifiers<'db> {
     pub(crate) place: Place<'db>,
     pub(crate) qualifiers: TypeQualifiers,
@@ -689,6 +689,51 @@ impl<'db> PlaceAndQualifiers<'db> {
             .or_else(|lookup_error| lookup_error.or_fall_back_to(db, fallback_fn()))
             .into()
     }
+
+    pub(crate) fn cycle_normalized(
+        self,
+        db: &'db dyn Db,
+        previous_place: Self,
+        cycle: &salsa::Cycle,
+    ) -> Self {
+        let place = match (previous_place.place, self.place) {
+            // In fixed-point iteration of type inference, the member type must be monotonically widened and not "oscillate".
+            // Here, monotonicity is guaranteed by pre-unioning the type of the previous iteration into the current result.
+            (Place::Defined(prev_ty, _, _), Place::Defined(ty, origin, definedness)) => {
+                Place::Defined(ty.cycle_normalized(db, prev_ty, cycle), origin, definedness)
+            }
+            // If a `Place` in the current cycle is `Defined` but `Undefined` in the previous cycle,
+            // that means that its definedness depends on the truthiness of the previous cycle value.
+            // In this case, the definedness of the current cycle `Place` is set to `PossiblyUndefined`.
+            // Actually, this branch is unreachable. We evaluate the truthiness of non-definitely-bound places as Ambiguous (see #19579),
+            // so convergence is guaranteed without resorting to this handling.
+            // However, the handling described above may reduce the exactness of reachability analysis,
+            // so it may be better to remove it. In that case, this branch is necessary.
+            (Place::Undefined, Place::Defined(ty, origin, _definedness)) => Place::Defined(
+                ty.recursive_type_normalized(db, cycle),
+                origin,
+                Definedness::PossiblyUndefined,
+            ),
+            // If a `Place` that was `Defined(Divergent)` in the previous cycle is actually found to be unreachable in the current cycle,
+            // it is set to `Undefined` (because the cycle initial value does not include meaningful reachability information).
+            (Place::Defined(ty, origin, _definedness), Place::Undefined) => {
+                if cycle.head_ids().any(|id| ty == Type::divergent(id)) {
+                    Place::Undefined
+                } else {
+                    Place::Defined(
+                        ty.recursive_type_normalized(db, cycle),
+                        origin,
+                        Definedness::PossiblyUndefined,
+                    )
+                }
+            }
+            (Place::Undefined, Place::Undefined) => Place::Undefined,
+        };
+        PlaceAndQualifiers {
+            place,
+            qualifiers: self.qualifiers,
+        }
+    }
 }
 
 impl<'db> From<Place<'db>> for PlaceAndQualifiers<'db> {
@@ -699,16 +744,30 @@ impl<'db> From<Place<'db>> for PlaceAndQualifiers<'db> {
 
 fn place_cycle_initial<'db>(
     _db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     _scope: ScopeId<'db>,
     _place_id: ScopedPlaceId,
     _requires_explicit_reexport: RequiresExplicitReExport,
     _considered_definitions: ConsideredDefinitions,
 ) -> PlaceAndQualifiers<'db> {
-    Place::bound(Type::Never).into()
+    Place::bound(Type::divergent(id)).into()
 }
 
-#[salsa::tracked(cycle_initial=place_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
+#[allow(clippy::too_many_arguments)]
+fn place_cycle_recover<'db>(
+    db: &'db dyn Db,
+    cycle: &salsa::Cycle,
+    previous_place: &PlaceAndQualifiers<'db>,
+    place: PlaceAndQualifiers<'db>,
+    _scope: ScopeId<'db>,
+    _place_id: ScopedPlaceId,
+    _requires_explicit_reexport: RequiresExplicitReExport,
+    _considered_definitions: ConsideredDefinitions,
+) -> PlaceAndQualifiers<'db> {
+    place.cycle_normalized(db, *previous_place, cycle)
+}
+
+#[salsa::tracked(cycle_fn=place_cycle_recover, cycle_initial=place_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
 pub(crate) fn place_by_id<'db>(
     db: &'db dyn Db,
     scope: ScopeId<'db>,

crates/ty_python_semantic/src/semantic_model.rs

@@ -12,8 +12,7 @@ use crate::module_resolver::{KnownModule, Module, list_modules, resolve_module};
 use crate::semantic_index::definition::Definition;
 use crate::semantic_index::scope::FileScopeId;
 use crate::semantic_index::semantic_index;
-use crate::types::ide_support::all_declarations_and_bindings;
+use crate::types::ide_support::{Member, all_declarations_and_bindings, all_members};
-use crate::types::ide_support::{Member, all_members};
 use crate::types::{Type, binding_type, infer_scope_types};
 
 /// The primary interface the LSP should use for querying semantic information about a [`File`].

crates/ty_python_semantic/src/types/bound_super.rs

@@ -172,7 +172,7 @@ impl<'db> BoundSuperError<'db> {
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, get_size2::GetSize)]
 pub enum SuperOwnerKind<'db> {
-    Dynamic(DynamicType<'db>),
+    Dynamic(DynamicType),
     Class(ClassType<'db>),
     Instance(NominalInstanceType<'db>),
 }
@@ -192,6 +192,26 @@ impl<'db> SuperOwnerKind<'db> {
         }
     }
 
+    fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        match self {
+            SuperOwnerKind::Dynamic(dynamic) => {
+                Some(SuperOwnerKind::Dynamic(dynamic.recursive_type_normalized()))
+            }
+            SuperOwnerKind::Class(class) => Some(SuperOwnerKind::Class(
+                class.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+            SuperOwnerKind::Instance(instance) => Some(SuperOwnerKind::Instance(
+                instance.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+        }
+    }
+
     fn iter_mro(self, db: &'db dyn Db) -> impl Iterator<Item = ClassBase<'db>> {
         match self {
             SuperOwnerKind::Dynamic(dynamic) => {
@@ -582,4 +602,20 @@ impl<'db> BoundSuperType<'db> {
             self.owner(db).normalized_impl(db, visitor),
         )
     }
+
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self::new(
+            db,
+            self.pivot_class(db)
+                .recursive_type_normalized_impl(db, div, nested, visitor)?,
+            self.owner(db)
+                .recursive_type_normalized_impl(db, div, nested, visitor)?,
+        ))
+    }
 }

crates/ty_python_semantic/src/types/builder.rs

@@ -214,6 +214,9 @@ pub(crate) struct UnionBuilder<'db> {
     db: &'db dyn Db,
     unpack_aliases: bool,
     order_elements: bool,
+    // This is enabled when joining types in a `cycle_recovery` function.
+    // Since a cycle cannot be created within a `cycle_recovery` function, execution of `is_redundant_with` is skipped.
+    cycle_recovery: bool,
 }
 
 impl<'db> UnionBuilder<'db> {
@@ -223,6 +226,7 @@ impl<'db> UnionBuilder<'db> {
             elements: vec![],
             unpack_aliases: true,
             order_elements: false,
+            cycle_recovery: false,
         }
     }
 
@@ -236,6 +240,14 @@ impl<'db> UnionBuilder<'db> {
         self
     }
 
+    pub(crate) fn cycle_recovery(mut self, val: bool) -> Self {
+        self.cycle_recovery = val;
+        if self.cycle_recovery {
+            self.unpack_aliases = false;
+        }
+        self
+    }
+
     pub(crate) fn is_empty(&self) -> bool {
         self.elements.is_empty()
     }
@@ -466,7 +478,7 @@ impl<'db> UnionBuilder<'db> {
         // If an alias gets here, it means we aren't unpacking aliases, and we also
         // shouldn't try to simplify aliases out of the union, because that will require
         // unpacking them.
-        let should_simplify_full = !matches!(ty, Type::TypeAlias(_));
+        let should_simplify_full = !matches!(ty, Type::TypeAlias(_)) && !self.cycle_recovery;
 
         let mut to_remove = SmallVec::<[usize; 2]>::new();
         let ty_negated = if should_simplify_full {

crates/ty_python_semantic/src/types/class.rs

@@ -6,7 +6,7 @@ use super::TypeVarVariance;
 use super::{
     BoundTypeVarInstance, IntersectionBuilder, MemberLookupPolicy, Mro, MroError, MroIterator,
     SpecialFormType, SubclassOfType, Truthiness, Type, TypeQualifiers, class_base::ClassBase,
-    function::FunctionType, infer_expression_type, infer_unpack_types,
+    function::FunctionType,
 };
 use crate::module_resolver::KnownModule;
 use crate::place::TypeOrigin;
@@ -25,7 +25,7 @@ use crate::types::function::{DataclassTransformerParams, KnownFunction};
 use crate::types::generics::{
     GenericContext, InferableTypeVars, Specialization, walk_generic_context, walk_specialization,
 };
-use crate::types::infer::nearest_enclosing_class;
+use crate::types::infer::{infer_expression_type, infer_unpack_types, nearest_enclosing_class};
 use crate::types::member::{Member, class_member};
 use crate::types::signatures::{CallableSignature, Parameter, Parameters, Signature};
 use crate::types::tuple::{TupleSpec, TupleType};
@@ -37,8 +37,7 @@ use crate::types::{
     HasRelationToVisitor, IsDisjointVisitor, IsEquivalentVisitor, KnownInstanceType,
     ManualPEP695TypeAliasType, MaterializationKind, NormalizedVisitor, PropertyInstanceType,
     StringLiteralType, TypeAliasType, TypeContext, TypeMapping, TypeRelation, TypedDictParams,
-    UnionBuilder, VarianceInferable, declaration_type, determine_upper_bound,
+    UnionBuilder, VarianceInferable, binding_type, declaration_type, determine_upper_bound,
-    exceeds_max_specialization_depth, infer_definition_types,
 };
 use crate::{
     Db, FxIndexMap, FxIndexSet, FxOrderSet, Program,
@@ -87,12 +86,30 @@ fn inheritance_cycle_initial<'db>(
 
 fn implicit_attribute_initial<'db>(
     _db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     _class_body_scope: ScopeId<'db>,
     _name: String,
     _target_method_decorator: MethodDecorator,
 ) -> Member<'db> {
-    Member::unbound()
+    Member {
+        inner: Place::bound(Type::divergent(id)).into(),
+    }
+}
+
+#[allow(clippy::too_many_arguments)]
+fn implicit_attribute_cycle_recover<'db>(
+    db: &'db dyn Db,
+    cycle: &salsa::Cycle,
+    previous_member: &Member<'db>,
+    member: Member<'db>,
+    _class_body_scope: ScopeId<'db>,
+    _name: String,
+    _target_method_decorator: MethodDecorator,
+) -> Member<'db> {
+    let inner = member
+        .inner
+        .cycle_normalized(db, previous_member.inner, cycle);
+    Member { inner }
 }
 
 fn try_mro_cycle_initial<'db>(
@@ -107,7 +124,6 @@ fn try_mro_cycle_initial<'db>(
     ))
 }
 
-#[allow(clippy::unnecessary_wraps)]
 fn is_typed_dict_cycle_initial<'db>(
     _db: &'db dyn Db,
     _id: salsa::Id,
@@ -127,6 +143,14 @@ fn try_metaclass_cycle_initial<'db>(
     })
 }
 
+fn decorators_cycle_initial<'db>(
+    _db: &'db dyn Db,
+    _id: salsa::Id,
+    _self: ClassLiteral<'db>,
+) -> Box<[Type<'db>]> {
+    Box::default()
+}
+
 fn fields_cycle_initial<'db>(
     _db: &'db dyn Db,
     _id: salsa::Id,
@@ -255,6 +279,21 @@ impl<'db> GenericAlias<'db> {
         )
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self::new(
+            db,
+            self.origin(db),
+            self.specialization(db)
+                .recursive_type_normalized_impl(db, div, nested, visitor)?,
+        ))
+    }
+
     pub(crate) fn definition(self, db: &'db dyn Db) -> Definition<'db> {
         self.origin(db).definition(db)
     }
@@ -399,6 +438,21 @@ impl<'db> ClassType<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        match self {
+            Self::NonGeneric(_) => Some(self),
+            Self::Generic(generic) => Some(Self::Generic(
+                generic.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+        }
+    }
+
     pub(super) fn has_pep_695_type_params(self, db: &'db dyn Db) -> bool {
         match self {
             Self::NonGeneric(class) => class.has_pep_695_type_params(db),
@@ -1533,17 +1587,7 @@ impl<'db> ClassLiteral<'db> {
         match self.generic_context(db) {
             None => ClassType::NonGeneric(self),
             Some(generic_context) => {
-                let mut specialization = f(generic_context);
+                let specialization = f(generic_context);
-
-                for (idx, ty) in specialization.types(db).iter().enumerate() {
-                    if exceeds_max_specialization_depth(db, *ty) {
-                        specialization = specialization.with_replaced_type(
-                            db,
-                            idx,
-                            Type::divergent(Some(self.body_scope(db))),
-                        );
-                    }
-                }
 
                 ClassType::Generic(GenericAlias::new(db, self, specialization))
             }
@@ -1698,7 +1742,7 @@ impl<'db> ClassLiteral<'db> {
     }
 
     /// Return the types of the decorators on this class
-    #[salsa::tracked(returns(deref), heap_size=ruff_memory_usage::heap_size)]
+    #[salsa::tracked(returns(deref), cycle_initial=decorators_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
     fn decorators(self, db: &'db dyn Db) -> Box<[Type<'db>]> {
         tracing::trace!("ClassLiteral::decorators: {}", self.name(db));
 
@@ -3136,10 +3180,12 @@ impl<'db> ClassLiteral<'db> {
         )
     }
 
-    #[salsa::tracked(cycle_initial=implicit_attribute_initial,
+    #[salsa::tracked(
+        cycle_fn=implicit_attribute_cycle_recover,
+        cycle_initial=implicit_attribute_initial,
         heap_size=ruff_memory_usage::heap_size,
     )]
-    fn implicit_attribute_inner(
+    pub(super) fn implicit_attribute_inner(
         db: &'db dyn Db,
         class_body_scope: ScopeId<'db>,
         name: String,
@@ -3159,7 +3205,6 @@ impl<'db> ClassLiteral<'db> {
         let index = semantic_index(db, file);
         let class_map = use_def_map(db, class_body_scope);
         let class_table = place_table(db, class_body_scope);
-
         let is_valid_scope = |method_scope: &Scope| {
             if let Some(method_def) = method_scope.node().as_function() {
                 let method_name = method_def.node(&module).name.as_str();
@@ -5468,8 +5513,7 @@ impl KnownClass {
                         };
 
                         let definition = index.expect_single_definition(first_param);
-                        let first_param =
+                        let first_param = binding_type(db, definition);
-                            infer_definition_types(db, definition).binding_type(definition);
 
                         let bound_super = BoundSuperType::build(
                             db,

crates/ty_python_semantic/src/types/class_base.rs

@@ -18,7 +18,7 @@ use crate::types::{
 /// automatically construct the default specialization for that class.
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, salsa::Update, get_size2::GetSize)]
 pub enum ClassBase<'db> {
-    Dynamic(DynamicType<'db>),
+    Dynamic(DynamicType),
     Class(ClassType<'db>),
     /// Although `Protocol` is not a class in typeshed's stubs, it is at runtime,
     /// and can appear in the MRO of a class.
@@ -43,6 +43,22 @@ impl<'db> ClassBase<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        match self {
+            Self::Dynamic(dynamic) => Some(Self::Dynamic(dynamic.recursive_type_normalized())),
+            Self::Class(class) => Some(Self::Class(
+                class.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+            Self::Protocol | Self::Generic | Self::TypedDict => Some(self),
+        }
+    }
+
     pub(crate) fn name(self, db: &'db dyn Db) -> &'db str {
         match self {
             ClassBase::Class(class) => class.name(db),

crates/ty_python_semantic/src/types/cyclic.rs

@@ -89,6 +89,23 @@ impl<Tag, T: Hash + Eq + Clone, R: Clone> CycleDetector<Tag, T, R> {
 
         ret
     }
+
+    pub fn try_visit(&self, item: T, func: impl FnOnce() -> Option<R>) -> Option<R> {
+        if let Some(val) = self.cache.borrow().get(&item) {
+            return Some(val.clone());
+        }
+
+        // We hit a cycle
+        if !self.seen.borrow_mut().insert(item.clone()) {
+            return Some(self.fallback.clone());
+        }
+
+        let ret = func()?;
+        self.seen.borrow_mut().pop();
+        self.cache.borrow_mut().insert(item, ret.clone());
+
+        Some(ret)
+    }
 }
 
 impl<Tag, T: Hash + Eq + Clone, R: Default + Clone> Default for CycleDetector<Tag, T, R> {

crates/ty_python_semantic/src/types/diagnostic.rs

@@ -54,6 +54,7 @@ pub(crate) fn register_lints(registry: &mut LintRegistryBuilder) {
     registry.register_lint(&CONFLICTING_DECLARATIONS);
     registry.register_lint(&CONFLICTING_METACLASS);
     registry.register_lint(&CYCLIC_CLASS_DEFINITION);
+    registry.register_lint(&CYCLIC_TYPE_ALIAS_DEFINITION);
     registry.register_lint(&DEPRECATED);
     registry.register_lint(&DIVISION_BY_ZERO);
     registry.register_lint(&DUPLICATE_BASE);
@@ -274,6 +275,28 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for type alias definitions that (directly or mutually) refer to themselves.
+    ///
+    /// ## Why is it bad?
+    /// Although it is permitted to define a recursive type alias, it is not meaningful
+    /// to have a type alias whose expansion can only result in itself, and is therefore not allowed.
+    ///
+    /// ## Examples
+    /// ```python
+    /// type Itself = Itself
+    ///
+    /// type A = B
+    /// type B = A
+    /// ```
+    pub(crate) static CYCLIC_TYPE_ALIAS_DEFINITION = {
+        summary: "detects cyclic type alias definitions",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// It detects division by zero.

crates/ty_python_semantic/src/types/function.rs

@@ -1053,6 +1053,34 @@ impl<'db> FunctionType<'db> {
             updated_last_definition_signature,
         )
     }
+
+    pub(crate) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        let literal = self.literal(db);
+        let updated_signature = match self.updated_signature(db) {
+            Some(signature) => {
+                Some(signature.recursive_type_normalized_impl(db, div, nested, visitor)?)
+            }
+            None => None,
+        };
+        let updated_last_definition_signature = match self.updated_last_definition_signature(db) {
+            Some(signature) => {
+                Some(signature.recursive_type_normalized_impl(db, div, nested, visitor)?)
+            }
+            None => None,
+        };
+        Some(Self::new(
+            db,
+            literal,
+            updated_signature,
+            updated_last_definition_signature,
+        ))
+    }
 }
 
 /// Evaluate an `isinstance` call. Return `Truthiness::AlwaysTrue` if we can definitely infer that

crates/ty_python_semantic/src/types/generics.rs

@@ -1073,6 +1073,41 @@ impl<'db> Specialization<'db> {
         )
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        let types = if nested {
+            self.types(db)
+                .iter()
+                .map(|ty| ty.recursive_type_normalized_impl(db, div, true, visitor))
+                .collect::<Option<Box<[_]>>>()?
+        } else {
+            self.types(db)
+                .iter()
+                .map(|ty| {
+                    ty.recursive_type_normalized_impl(db, div, true, visitor)
+                        .unwrap_or(div)
+                })
+                .collect::<Box<[_]>>()
+        };
+        let tuple_inner = match self.tuple_inner(db) {
+            Some(tuple) => Some(tuple.recursive_type_normalized_impl(db, div, nested, visitor)?),
+            None => None,
+        };
+        let context = self.generic_context(db);
+        Some(Self::new(
+            db,
+            context,
+            types,
+            self.materialization_kind(db),
+            tuple_inner,
+        ))
+    }
+
     pub(super) fn materialize_impl(
         self,
         db: &'db dyn Db,
@@ -1281,25 +1316,6 @@ impl<'db> Specialization<'db> {
         // A tuple's specialization will include all of its element types, so we don't need to also
         // look in `self.tuple`.
     }
-
-    /// Returns a copy of this specialization with the type at a given index replaced.
-    pub(crate) fn with_replaced_type(
-        self,
-        db: &'db dyn Db,
-        index: usize,
-        new_type: Type<'db>,
-    ) -> Self {
-        let mut new_types: Box<[_]> = self.types(db).to_vec().into_boxed_slice();
-        new_types[index] = new_type;
-
-        Self::new(
-            db,
-            self.generic_context(db),
-            new_types,
-            self.materialization_kind(db),
-            self.tuple_inner(db),
-        )
-    }
 }
 
 /// A mapping between type variables and types.

crates/ty_python_semantic/src/types/infer.rs

@@ -31,7 +31,7 @@
 //!
 //! Many of our type inference Salsa queries implement cycle recovery via fixed-point iteration. In
 //! general, they initiate fixed-point iteration by returning an `Inference` type that returns
-//! `Type::Never` for all expressions, bindings, and declarations, and then they continue iterating
+//! the `Divergent` type for all expressions, bindings, and declarations, and then they continue iterating
 //! the query cycle until a fixed-point is reached. Salsa has a built-in fixed limit on the number
 //! of iterations, so if we fail to converge, Salsa will eventually panic. (This should of course
 //! be considered a bug.)
@@ -52,7 +52,9 @@ use crate::types::diagnostic::TypeCheckDiagnostics;
 use crate::types::function::FunctionType;
 use crate::types::generics::Specialization;
 use crate::types::unpacker::{UnpackResult, Unpacker};
-use crate::types::{ClassLiteral, KnownClass, Truthiness, Type, TypeAndQualifiers};
+use crate::types::{
+    ClassLiteral, KnownClass, Truthiness, Type, TypeAndQualifiers, declaration_type,
+};
 use crate::unpack::Unpack;
 use builder::TypeInferenceBuilder;
 
@@ -60,13 +62,10 @@ mod builder;
 #[cfg(test)]
 mod tests;
 
-/// How many fixpoint iterations to allow before falling back to Divergent type.
-const ITERATIONS_BEFORE_FALLBACK: u32 = 10;
-
 /// Infer all types for a [`ScopeId`], including all definitions and expressions in that scope.
 /// Use when checking a scope, or needing to provide a type for an arbitrary expression in the
 /// scope.
-#[salsa::tracked(returns(ref), cycle_initial=scope_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
+#[salsa::tracked(returns(ref), cycle_fn=scope_cycle_recover, cycle_initial=scope_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
 pub(crate) fn infer_scope_types<'db>(db: &'db dyn Db, scope: ScopeId<'db>) -> ScopeInference<'db> {
     let file = scope.file(db);
     let _span = tracing::trace_span!("infer_scope_types", scope=?scope.as_id(), ?file).entered();
@@ -80,12 +79,22 @@ pub(crate) fn infer_scope_types<'db>(db: &'db dyn Db, scope: ScopeId<'db>) -> Sc
     TypeInferenceBuilder::new(db, InferenceRegion::Scope(scope), index, &module).finish_scope()
 }
 
+fn scope_cycle_recover<'db>(
+    db: &'db dyn Db,
+    cycle: &salsa::Cycle,
+    previous_inference: &ScopeInference<'db>,
+    inference: ScopeInference<'db>,
+    _scope: ScopeId<'db>,
+) -> ScopeInference<'db> {
+    inference.cycle_normalized(db, previous_inference, cycle)
+}
+
 fn scope_cycle_initial<'db>(
     _db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
-    scope: ScopeId<'db>,
+    _scope: ScopeId<'db>,
 ) -> ScopeInference<'db> {
-    ScopeInference::cycle_initial(scope)
+    ScopeInference::cycle_initial(Type::divergent(id))
 }
 
 /// Infer all types for a [`Definition`] (including sub-expressions).
@@ -113,30 +122,26 @@ pub(crate) fn infer_definition_types<'db>(
 fn definition_cycle_recover<'db>(
     db: &'db dyn Db,
     cycle: &salsa::Cycle,
-    last_provisional_value: &DefinitionInference<'db>,
+    previous_inference: &DefinitionInference<'db>,
-    value: DefinitionInference<'db>,
+    inference: DefinitionInference<'db>,
-    definition: Definition<'db>,
+    _definition: Definition<'db>,
 ) -> DefinitionInference<'db> {
-    if &value == last_provisional_value || cycle.iteration() != ITERATIONS_BEFORE_FALLBACK {
+    inference.cycle_normalized(db, previous_inference, cycle)
-        value
-    } else {
-        DefinitionInference::cycle_fallback(definition.scope(db))
-    }
 }
 
 fn definition_cycle_initial<'db>(
     db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     definition: Definition<'db>,
 ) -> DefinitionInference<'db> {
-    DefinitionInference::cycle_initial(definition.scope(db))
+    DefinitionInference::cycle_initial(definition.scope(db), Type::divergent(id))
 }
 
 /// Infer types for all deferred type expressions in a [`Definition`].
 ///
 /// Deferred expressions are type expressions (annotations, base classes, aliases...) in a stub
 /// file, or in a file with `from __future__ import annotations`, or stringified annotations.
-#[salsa::tracked(returns(ref), cycle_initial=deferred_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
+#[salsa::tracked(returns(ref), cycle_fn=deferred_cycle_recovery, cycle_initial=deferred_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
 pub(crate) fn infer_deferred_types<'db>(
     db: &'db dyn Db,
     definition: Definition<'db>,
@@ -157,12 +162,22 @@ pub(crate) fn infer_deferred_types<'db>(
         .finish_definition()
 }
 
+fn deferred_cycle_recovery<'db>(
+    db: &'db dyn Db,
+    cycle: &salsa::Cycle,
+    previous_inference: &DefinitionInference<'db>,
+    inference: DefinitionInference<'db>,
+    _definition: Definition<'db>,
+) -> DefinitionInference<'db> {
+    inference.cycle_normalized(db, previous_inference, cycle)
+}
+
 fn deferred_cycle_initial<'db>(
     db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     definition: Definition<'db>,
 ) -> DefinitionInference<'db> {
-    DefinitionInference::cycle_initial(definition.scope(db))
+    DefinitionInference::cycle_initial(definition.scope(db), Type::divergent(id))
 }
 
 /// Infer all types for an [`Expression`] (including sub-expressions).
@@ -178,7 +193,7 @@ pub(crate) fn infer_expression_types<'db>(
 }
 
 #[salsa::tracked(returns(ref), cycle_fn=expression_cycle_recover, cycle_initial=expression_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
-fn infer_expression_types_impl<'db>(
+pub(super) fn infer_expression_types_impl<'db>(
     db: &'db dyn Db,
     input: InferExpression<'db>,
 ) -> ExpressionInference<'db> {
@@ -208,23 +223,20 @@ fn infer_expression_types_impl<'db>(
 fn expression_cycle_recover<'db>(
     db: &'db dyn Db,
     cycle: &salsa::Cycle,
-    last_provisional_value: &ExpressionInference<'db>,
+    previous_inference: &ExpressionInference<'db>,
-    value: ExpressionInference<'db>,
+    inference: ExpressionInference<'db>,
-    input: InferExpression<'db>,
+    _input: InferExpression<'db>,
 ) -> ExpressionInference<'db> {
-    if &value == last_provisional_value || cycle.iteration() != ITERATIONS_BEFORE_FALLBACK {
+    inference.cycle_normalized(db, previous_inference, cycle)
-        value
-    } else {
-        ExpressionInference::cycle_fallback(input.expression(db).scope(db))
-    }
 }
 
 fn expression_cycle_initial<'db>(
     db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     input: InferExpression<'db>,
 ) -> ExpressionInference<'db> {
-    ExpressionInference::cycle_initial(input.expression(db).scope(db))
+    let cycle_recovery = Type::divergent(id);
+    ExpressionInference::cycle_initial(input.expression(db).scope(db), cycle_recovery)
 }
 
 /// Infers the type of an `expression` that is guaranteed to be in the same file as the calling query.
@@ -232,7 +244,7 @@ fn expression_cycle_initial<'db>(
 /// This is a small helper around [`infer_expression_types()`] to reduce the boilerplate.
 /// Use [`infer_expression_type()`] if it isn't guaranteed that `expression` is in the same file to
 /// avoid cross-file query dependencies.
-pub(super) fn infer_same_file_expression_type<'db>(
+pub(crate) fn infer_same_file_expression_type<'db>(
     db: &'db dyn Db,
     expression: Expression<'db>,
     tcx: TypeContext<'db>,
@@ -257,22 +269,33 @@ pub(crate) fn infer_expression_type<'db>(
     infer_expression_type_impl(db, InferExpression::new(db, expression, tcx))
 }
 
-#[salsa::tracked(cycle_initial=single_expression_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
+#[salsa::tracked(cycle_fn=single_expression_cycle_recover, cycle_initial=single_expression_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
 fn infer_expression_type_impl<'db>(db: &'db dyn Db, input: InferExpression<'db>) -> Type<'db> {
     let file = input.expression(db).file(db);
     let module = parsed_module(db, file).load(db);
 
     // It's okay to call the "same file" version here because we're inside a salsa query.
     let inference = infer_expression_types_impl(db, input);
+
     inference.expression_type(input.expression(db).node_ref(db, &module))
 }
 
+fn single_expression_cycle_recover<'db>(
+    db: &'db dyn Db,
+    cycle: &salsa::Cycle,
+    previous_cycle_value: &Type<'db>,
+    result: Type<'db>,
+    _input: InferExpression<'db>,
+) -> Type<'db> {
+    result.cycle_normalized(db, *previous_cycle_value, cycle)
+}
+
 fn single_expression_cycle_initial<'db>(
     _db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     _input: InferExpression<'db>,
 ) -> Type<'db> {
-    Type::Never
+    Type::divergent(id)
 }
 
 /// An `Expression` with an optional `TypeContext`.
@@ -280,13 +303,13 @@ fn single_expression_cycle_initial<'db>(
 /// This is a Salsa supertype used as the input to `infer_expression_types` to avoid
 /// interning an `ExpressionWithContext` unnecessarily when no type context is provided.
 #[derive(Debug, Clone, Copy, Eq, Hash, PartialEq, salsa::Supertype, salsa::Update)]
-enum InferExpression<'db> {
+pub(super) enum InferExpression<'db> {
     Bare(Expression<'db>),
     WithContext(ExpressionWithContext<'db>),
 }
 
 impl<'db> InferExpression<'db> {
-    fn new(
+    pub(super) fn new(
         db: &'db dyn Db,
         expression: Expression<'db>,
         tcx: TypeContext<'db>,
@@ -320,7 +343,7 @@ impl<'db> InferExpression<'db> {
 
 /// An `Expression` with a `TypeContext`.
 #[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
-struct ExpressionWithContext<'db> {
+pub(super) struct ExpressionWithContext<'db> {
     expression: Expression<'db>,
     tcx: TypeContext<'db>,
 }
@@ -381,7 +404,6 @@ pub(crate) fn static_expression_truthiness<'db>(
     let file = expression.file(db);
     let module = parsed_module(db, file).load(db);
     let node = expression.node_ref(db, &module);
-
     inference.expression_type(node).bool(db)
 }
 
@@ -399,7 +421,7 @@ fn static_expression_truthiness_cycle_initial<'db>(
 /// involved in an unpacking operation. It returns a result-like object that can be used to get the
 /// type of the variables involved in this unpacking along with any violations that are detected
 /// during this unpacking.
-#[salsa::tracked(returns(ref), cycle_initial=unpack_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
+#[salsa::tracked(returns(ref), cycle_fn=unpack_cycle_recover, cycle_initial=unpack_cycle_initial, heap_size=ruff_memory_usage::heap_size)]
 pub(super) fn infer_unpack_types<'db>(db: &'db dyn Db, unpack: Unpack<'db>) -> UnpackResult<'db> {
     let file = unpack.file(db);
     let module = parsed_module(db, file).load(db);
@@ -413,10 +435,20 @@ pub(super) fn infer_unpack_types<'db>(db: &'db dyn Db, unpack: Unpack<'db>) -> U
 
 fn unpack_cycle_initial<'db>(
     _db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     _unpack: Unpack<'db>,
 ) -> UnpackResult<'db> {
-    UnpackResult::cycle_initial(Type::Never)
+    UnpackResult::cycle_initial(Type::divergent(id))
+}
+
+fn unpack_cycle_recover<'db>(
+    db: &'db dyn Db,
+    cycle: &salsa::Cycle,
+    previous_cycle_result: &UnpackResult<'db>,
+    result: UnpackResult<'db>,
+    _unpack: Unpack<'db>,
+) -> UnpackResult<'db> {
+    result.cycle_normalized(db, previous_cycle_result, cycle)
 }
 
 /// Returns the type of the nearest enclosing class for the given scope.
@@ -438,8 +470,7 @@ pub(crate) fn nearest_enclosing_class<'db>(
         .find_map(|(_, ancestor_scope)| {
             let class = ancestor_scope.node().as_class()?;
             let definition = semantic.expect_single_definition(class);
-            infer_definition_types(db, definition)
+            declaration_type(db, definition)
-                .declaration_type(definition)
                 .inner_type()
                 .as_class_literal()
         })
@@ -494,35 +525,6 @@ impl<'db> InferenceRegion<'db> {
     }
 }
 
-#[derive(Debug, Clone, Copy, Eq, PartialEq, get_size2::GetSize, salsa::Update)]
-enum CycleRecovery<'db> {
-    /// An initial-value for fixpoint iteration; all types are `Type::Never`.
-    Initial,
-    /// A divergence-fallback value for fixpoint iteration; all types are `Divergent`.
-    Divergent(ScopeId<'db>),
-}
-
-impl<'db> CycleRecovery<'db> {
-    fn merge(self, other: Option<CycleRecovery<'db>>) -> Self {
-        if let Some(other) = other {
-            match (self, other) {
-                // It's important here that we keep the scope of `self` if merging two `Divergent`.
-                (Self::Divergent(scope), _) | (_, Self::Divergent(scope)) => Self::Divergent(scope),
-                _ => Self::Initial,
-            }
-        } else {
-            self
-        }
-    }
-
-    fn fallback_type(self) -> Type<'db> {
-        match self {
-            Self::Initial => Type::Never,
-            Self::Divergent(scope) => Type::divergent(Some(scope)),
-        }
-    }
-}
-
 /// The inferred types for a scope region.
 #[derive(Debug, Eq, PartialEq, salsa::Update, get_size2::GetSize)]
 pub(crate) struct ScopeInference<'db> {
@@ -538,26 +540,38 @@ struct ScopeInferenceExtra<'db> {
     /// String annotations found in this region
     string_annotations: FxHashSet<ExpressionNodeKey>,
 
-    /// Is this a cycle-recovery inference result, and if so, what kind?
+    /// The fallback type for missing expressions/bindings/declarations or recursive type inference.
-    cycle_recovery: Option<CycleRecovery<'db>>,
+    cycle_recovery: Option<Type<'db>>,
 
     /// The diagnostics for this region.
     diagnostics: TypeCheckDiagnostics,
 }
 
 impl<'db> ScopeInference<'db> {
-    fn cycle_initial(scope: ScopeId<'db>) -> Self {
+    fn cycle_initial(cycle_recovery: Type<'db>) -> Self {
-        let _ = scope;
-
         Self {
             extra: Some(Box::new(ScopeInferenceExtra {
-                cycle_recovery: Some(CycleRecovery::Initial),
+                cycle_recovery: Some(cycle_recovery),
                 ..ScopeInferenceExtra::default()
             })),
             expressions: FxHashMap::default(),
         }
     }
 
+    fn cycle_normalized(
+        mut self,
+        db: &'db dyn Db,
+        previous_inference: &ScopeInference<'db>,
+        cycle: &salsa::Cycle,
+    ) -> ScopeInference<'db> {
+        for (expr, ty) in &mut self.expressions {
+            let previous_ty = previous_inference.expression_type(*expr);
+            *ty = ty.cycle_normalized(db, previous_ty, cycle);
+        }
+
+        self
+    }
+
     pub(crate) fn diagnostics(&self) -> Option<&TypeCheckDiagnostics> {
         self.extra.as_deref().map(|extra| &extra.diagnostics)
     }
@@ -578,9 +592,7 @@ impl<'db> ScopeInference<'db> {
     }
 
     fn fallback_type(&self) -> Option<Type<'db>> {
-        self.extra
+        self.extra.as_ref().and_then(|extra| extra.cycle_recovery)
-            .as_ref()
-            .and_then(|extra| extra.cycle_recovery.map(CycleRecovery::fallback_type))
     }
 
     /// Returns whether the given expression is a string annotation
@@ -608,7 +620,7 @@ pub(crate) struct DefinitionInference<'db> {
     ///
     /// Almost all definition regions have less than 10 bindings. There are very few with more than 10 (but still less than 20).
     /// Because of that, use a slice with linear search over a hash map.
-    bindings: Box<[(Definition<'db>, Type<'db>)]>,
+    pub(crate) bindings: Box<[(Definition<'db>, Type<'db>)]>,
 
     /// The types and type qualifiers of every declaration in this region.
     ///
@@ -626,8 +638,8 @@ struct DefinitionInferenceExtra<'db> {
     /// String annotations found in this region
     string_annotations: FxHashSet<ExpressionNodeKey>,
 
-    /// Is this a cycle-recovery inference result, and if so, what kind?
+    /// The fallback type for missing expressions/bindings/declarations or recursive type inference.
-    cycle_recovery: Option<CycleRecovery<'db>>,
+    cycle_recovery: Option<Type<'db>>,
 
     /// The definitions that have some deferred parts.
     deferred: Box<[Definition<'db>]>,
@@ -640,7 +652,7 @@ struct DefinitionInferenceExtra<'db> {
 }
 
 impl<'db> DefinitionInference<'db> {
-    fn cycle_initial(scope: ScopeId<'db>) -> Self {
+    fn cycle_initial(scope: ScopeId<'db>, cycle_recovery: Type<'db>) -> Self {
         let _ = scope;
 
         Self {
@@ -650,26 +662,49 @@ impl<'db> DefinitionInference<'db> {
             #[cfg(debug_assertions)]
             scope,
             extra: Some(Box::new(DefinitionInferenceExtra {
-                cycle_recovery: Some(CycleRecovery::Initial),
+                cycle_recovery: Some(cycle_recovery),
                 ..DefinitionInferenceExtra::default()
             })),
         }
     }
 
-    fn cycle_fallback(scope: ScopeId<'db>) -> Self {
+    fn cycle_normalized(
-        let _ = scope;
+        mut self,
-
+        db: &'db dyn Db,
-        Self {
+        previous_inference: &DefinitionInference<'db>,
-            expressions: FxHashMap::default(),
+        cycle: &salsa::Cycle,
-            bindings: Box::default(),
+    ) -> DefinitionInference<'db> {
-            declarations: Box::default(),
+        for (expr, ty) in &mut self.expressions {
-            #[cfg(debug_assertions)]
+            let previous_ty = previous_inference.expression_type(*expr);
-            scope,
+            *ty = ty.cycle_normalized(db, previous_ty, cycle);
-            extra: Some(Box::new(DefinitionInferenceExtra {
-                cycle_recovery: Some(CycleRecovery::Divergent(scope)),
-                ..DefinitionInferenceExtra::default()
-            })),
         }
+        for (binding, binding_ty) in &mut self.bindings {
+            if let Some((_, previous_binding)) = previous_inference
+                .bindings
+                .iter()
+                .find(|(previous_binding, _)| previous_binding == binding)
+            {
+                *binding_ty = binding_ty.cycle_normalized(db, *previous_binding, cycle);
+            } else {
+                *binding_ty = binding_ty.recursive_type_normalized(db, cycle);
+            }
+        }
+        for (declaration, declaration_ty) in &mut self.declarations {
+            if let Some((_, previous_declaration)) = previous_inference
+                .declarations
+                .iter()
+                .find(|(previous_declaration, _)| previous_declaration == declaration)
+            {
+                *declaration_ty = declaration_ty.map_type(|decl_ty| {
+                    decl_ty.cycle_normalized(db, previous_declaration.inner_type(), cycle)
+                });
+            } else {
+                *declaration_ty =
+                    declaration_ty.map_type(|decl_ty| decl_ty.recursive_type_normalized(db, cycle));
+            }
+        }
+
+        self
     }
 
     pub(crate) fn expression_type(&self, expression: impl Into<ExpressionNodeKey>) -> Type<'db> {
@@ -735,10 +770,8 @@ impl<'db> DefinitionInference<'db> {
         self.declarations.iter().map(|(_, qualifiers)| *qualifiers)
     }
 
-    fn fallback_type(&self) -> Option<Type<'db>> {
+    pub(crate) fn fallback_type(&self) -> Option<Type<'db>> {
-        self.extra
+        self.extra.as_ref().and_then(|extra| extra.cycle_recovery)
-            .as_ref()
-            .and_then(|extra| extra.cycle_recovery.map(CycleRecovery::fallback_type))
     }
 
     pub(crate) fn undecorated_type(&self) -> Option<Type<'db>> {
@@ -773,42 +806,55 @@ struct ExpressionInferenceExtra<'db> {
     /// The diagnostics for this region.
     diagnostics: TypeCheckDiagnostics,
 
-    /// Is this a cycle recovery inference result, and if so, what kind?
+    /// The fallback type for missing expressions/bindings/declarations or recursive type inference.
-    cycle_recovery: Option<CycleRecovery<'db>>,
+    cycle_recovery: Option<Type<'db>>,
 
     /// `true` if all places in this expression are definitely bound
     all_definitely_bound: bool,
 }
 
 impl<'db> ExpressionInference<'db> {
-    fn cycle_initial(scope: ScopeId<'db>) -> Self {
+    fn cycle_initial(scope: ScopeId<'db>, cycle_recovery: Type<'db>) -> Self {
         let _ = scope;
         Self {
             extra: Some(Box::new(ExpressionInferenceExtra {
-                cycle_recovery: Some(CycleRecovery::Initial),
+                cycle_recovery: Some(cycle_recovery),
                 all_definitely_bound: true,
                 ..ExpressionInferenceExtra::default()
             })),
             expressions: FxHashMap::default(),
-
             #[cfg(debug_assertions)]
             scope,
         }
     }
 
-    fn cycle_fallback(scope: ScopeId<'db>) -> Self {
+    fn cycle_normalized(
-        let _ = scope;
+        mut self,
-        Self {
+        db: &'db dyn Db,
-            extra: Some(Box::new(ExpressionInferenceExtra {
+        previous: &ExpressionInference<'db>,
-                cycle_recovery: Some(CycleRecovery::Divergent(scope)),
+        cycle: &salsa::Cycle,
-                all_definitely_bound: true,
+    ) -> ExpressionInference<'db> {
-                ..ExpressionInferenceExtra::default()
+        if let Some(extra) = self.extra.as_mut() {
-            })),
+            for (binding, binding_ty) in &mut extra.bindings {
-            expressions: FxHashMap::default(),
+                if let Some((_, previous_binding)) = previous.extra.as_deref().and_then(|extra| {
-
+                    extra
-            #[cfg(debug_assertions)]
+                        .bindings
-            scope,
+                        .iter()
+                        .find(|(previous_binding, _)| previous_binding == binding)
+                }) {
+                    *binding_ty = binding_ty.cycle_normalized(db, *previous_binding, cycle);
+                } else {
+                    *binding_ty = binding_ty.recursive_type_normalized(db, cycle);
+                }
+            }
         }
+
+        for (expr, ty) in &mut self.expressions {
+            let previous_ty = previous.expression_type(*expr);
+            *ty = ty.cycle_normalized(db, previous_ty, cycle);
+        }
+
+        self
     }
 
     pub(crate) fn try_expression_type(
@@ -827,9 +873,7 @@ impl<'db> ExpressionInference<'db> {
     }
 
     fn fallback_type(&self) -> Option<Type<'db>> {
-        self.extra
+        self.extra.as_ref().and_then(|extra| extra.cycle_recovery)
-            .as_ref()
-            .and_then(|extra| extra.cycle_recovery.map(CycleRecovery::fallback_type))
     }
 
     /// Returns true if all places in this expression are definitely bound.

crates/ty_python_semantic/src/types/infer/builder.rs

@@ -14,10 +14,10 @@ use rustc_hash::{FxHashMap, FxHashSet};
 use smallvec::SmallVec;
 
 use super::{
-    CycleRecovery, DefinitionInference, DefinitionInferenceExtra, ExpressionInference,
+    DefinitionInference, DefinitionInferenceExtra, ExpressionInference, ExpressionInferenceExtra,
-    ExpressionInferenceExtra, InferenceRegion, ScopeInference, ScopeInferenceExtra,
+    InferenceRegion, ScopeInference, ScopeInferenceExtra, infer_deferred_types,
-    infer_deferred_types, infer_definition_types, infer_expression_types,
+    infer_definition_types, infer_expression_types, infer_same_file_expression_type,
-    infer_same_file_expression_type, infer_scope_types, infer_unpack_types,
+    infer_unpack_types,
 };
 use crate::diagnostic::format_enumeration;
 use crate::module_name::{ModuleName, ModuleNameResolutionError};
@@ -56,16 +56,16 @@ use crate::types::context::{InNoTypeCheck, InferContext};
 use crate::types::cyclic::CycleDetector;
 use crate::types::diagnostic::{
     CALL_NON_CALLABLE, CONFLICTING_DECLARATIONS, CONFLICTING_METACLASS, CYCLIC_CLASS_DEFINITION,
-    DIVISION_BY_ZERO, DUPLICATE_KW_ONLY, INCONSISTENT_MRO, INVALID_ARGUMENT_TYPE,
+    CYCLIC_TYPE_ALIAS_DEFINITION, DIVISION_BY_ZERO, DUPLICATE_KW_ONLY, INCONSISTENT_MRO,
-    INVALID_ASSIGNMENT, INVALID_ATTRIBUTE_ACCESS, INVALID_BASE, INVALID_DECLARATION,
+    INVALID_ARGUMENT_TYPE, INVALID_ASSIGNMENT, INVALID_ATTRIBUTE_ACCESS, INVALID_BASE,
-    INVALID_GENERIC_CLASS, INVALID_KEY, INVALID_LEGACY_TYPE_VARIABLE, INVALID_METACLASS,
+    INVALID_DECLARATION, INVALID_GENERIC_CLASS, INVALID_KEY, INVALID_LEGACY_TYPE_VARIABLE,
-    INVALID_NAMED_TUPLE, INVALID_NEWTYPE, INVALID_OVERLOAD, INVALID_PARAMETER_DEFAULT,
+    INVALID_METACLASS, INVALID_NAMED_TUPLE, INVALID_NEWTYPE, INVALID_OVERLOAD,
-    INVALID_PARAMSPEC, INVALID_PROTOCOL, INVALID_TYPE_FORM, INVALID_TYPE_GUARD_CALL,
+    INVALID_PARAMETER_DEFAULT, INVALID_PARAMSPEC, INVALID_PROTOCOL, INVALID_TYPE_FORM,
-    INVALID_TYPE_VARIABLE_CONSTRAINTS, IncompatibleBases, NON_SUBSCRIPTABLE,
+    INVALID_TYPE_GUARD_CALL, INVALID_TYPE_VARIABLE_CONSTRAINTS, IncompatibleBases,
-    POSSIBLY_MISSING_ATTRIBUTE, POSSIBLY_MISSING_IMPLICIT_CALL, POSSIBLY_MISSING_IMPORT,
+    NON_SUBSCRIPTABLE, POSSIBLY_MISSING_ATTRIBUTE, POSSIBLY_MISSING_IMPLICIT_CALL,
-    SUBCLASS_OF_FINAL_CLASS, UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE, UNRESOLVED_GLOBAL,
+    POSSIBLY_MISSING_IMPORT, SUBCLASS_OF_FINAL_CLASS, UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE,
-    UNRESOLVED_IMPORT, UNRESOLVED_REFERENCE, UNSUPPORTED_OPERATOR, USELESS_OVERLOAD_BODY,
+    UNRESOLVED_GLOBAL, UNRESOLVED_IMPORT, UNRESOLVED_REFERENCE, UNSUPPORTED_OPERATOR,
-    hint_if_stdlib_attribute_exists_on_other_versions,
+    USELESS_OVERLOAD_BODY, hint_if_stdlib_attribute_exists_on_other_versions,
     hint_if_stdlib_submodule_exists_on_other_versions, report_attempted_protocol_instantiation,
     report_bad_dunder_set_call, report_cannot_pop_required_field_on_typed_dict,
     report_duplicate_bases, report_implicit_return_type, report_index_out_of_bounds,
@@ -92,7 +92,7 @@ use crate::types::infer::nearest_enclosing_function;
 use crate::types::instance::SliceLiteral;
 use crate::types::mro::MroErrorKind;
 use crate::types::newtype::NewType;
-use crate::types::signatures::Signature;
+use crate::types::signatures::{Parameter, Parameters, Signature};
 use crate::types::subclass_of::SubclassOfInner;
 use crate::types::tuple::{Tuple, TupleLength, TupleSpec, TupleType};
 use crate::types::typed_dict::{
@@ -104,11 +104,11 @@ use crate::types::{
     CallDunderError, CallableBinding, CallableType, CallableTypes, ClassLiteral, ClassType,
     DataclassParams, DynamicType, InternedType, IntersectionBuilder, IntersectionType, KnownClass,
     KnownInstanceType, LintDiagnosticGuard, MemberLookupPolicy, MetaclassCandidate,
-    PEP695TypeAliasType, Parameter, ParameterForm, Parameters, SpecialFormType, SubclassOfType,
+    PEP695TypeAliasType, ParameterForm, SpecialFormType, SubclassOfType, TrackedConstraintSet,
-    TrackedConstraintSet, Truthiness, Type, TypeAliasType, TypeAndQualifiers, TypeContext,
+    Truthiness, Type, TypeAliasType, TypeAndQualifiers, TypeContext, TypeQualifiers,
-    TypeQualifiers, TypeVarBoundOrConstraintsEvaluation, TypeVarDefaultEvaluation, TypeVarIdentity,
+    TypeVarBoundOrConstraintsEvaluation, TypeVarDefaultEvaluation, TypeVarIdentity,
     TypeVarInstance, TypeVarKind, TypeVarVariance, TypedDictType, UnionBuilder, UnionType,
-    UnionTypeInstance, binding_type, liskov, todo_type,
+    UnionTypeInstance, binding_type, infer_scope_types, liskov, todo_type,
 };
 use crate::types::{ClassBase, add_inferred_python_version_hint_to_diagnostic};
 use crate::unpack::{EvaluationMode, UnpackPosition};
@@ -288,11 +288,16 @@ pub(super) struct TypeInferenceBuilder<'db, 'ast> {
 
     multi_inference_state: MultiInferenceState,
 
+    /// If you cannot avoid the possibility of calling `infer(_type)_expression` multiple times for a given expression,
+    /// set this to `Get` after the expression has been inferred for the first time.
+    /// While this is `Get`, any expressions will be considered to have already been inferred.
+    inner_expression_inference_state: InnerExpressionInferenceState,
+
     /// For function definitions, the undecorated type of the function.
     undecorated_type: Option<Type<'db>>,
 
-    /// Did we merge in a sub-region with a cycle-recovery fallback, and if so, what kind?
+    /// The fallback type for missing expressions/bindings/declarations or recursive type inference.
-    cycle_recovery: Option<CycleRecovery<'db>>,
+    cycle_recovery: Option<Type<'db>>,
 
     /// `true` if all places in this expression are definitely bound
     all_definitely_bound: bool,
@@ -327,6 +332,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             called_functions: FxIndexSet::default(),
             deferred_state: DeferredExpressionState::None,
             multi_inference_state: MultiInferenceState::Panic,
+            inner_expression_inference_state: InnerExpressionInferenceState::Infer,
             expressions: FxHashMap::default(),
             string_annotations: FxHashSet::default(),
             bindings: VecMap::default(),
@@ -340,15 +346,22 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         }
     }
 
-    fn extend_cycle_recovery(&mut self, other_recovery: Option<CycleRecovery<'db>>) {
+    fn fallback_type(&self) -> Option<Type<'db>> {
-        match &mut self.cycle_recovery {
+        self.cycle_recovery
-            Some(recovery) => *recovery = recovery.merge(other_recovery),
-            recovery @ None => *recovery = other_recovery,
-        }
     }
 
-    fn fallback_type(&self) -> Option<Type<'db>> {
+    fn extend_cycle_recovery(&mut self, other: Option<Type<'db>>) {
-        self.cycle_recovery.map(CycleRecovery::fallback_type)
+        if let Some(other) = other {
+            match self.cycle_recovery {
+                Some(existing) => {
+                    self.cycle_recovery =
+                        Some(UnionType::from_elements(self.db(), [existing, other]));
+                }
+                None => {
+                    self.cycle_recovery = Some(other);
+                }
+            }
+        }
     }
 
     fn extend_definition(&mut self, inference: &DefinitionInference<'db>) {
@@ -1905,7 +1918,38 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
     }
 
     fn infer_type_alias(&mut self, type_alias: &ast::StmtTypeAlias) {
-        self.infer_annotation_expression(&type_alias.value, DeferredExpressionState::None);
+        let value_ty =
+            self.infer_annotation_expression(&type_alias.value, DeferredExpressionState::None);
+
+        // A type alias where a value type points to itself, i.e. the expanded type is `Divergent` is meaningless
+        // (but a type alias that expands to something like `list[Divergent]` may be a valid recursive type alias)
+        // and would lead to infinite recursion. Therefore, such type aliases should not be exposed.
+        // ```python
+        // type Itself = Itself  # error: "Cyclic definition of `Itself`"
+        // type A = B  # error: "Cyclic definition of `A`"
+        // type B = A  # error: "Cyclic definition of `B`"
+        // type G[T] = G[T]  # error: "Cyclic definition of `G`"
+        // type RecursiveList[T] = list[T | RecursiveList[T]]  # OK
+        // type RecursiveList2[T] = list[RecursiveList2[T]]  # It's not possible to create an element of this, but it's not an error for now
+        // type IntOr = int | IntOr  # It's redundant, but OK for now
+        // type IntOrStr = int | StrOrInt  # It's redundant, but OK
+        // type StrOrInt = str | IntOrStr  # It's redundant, but OK
+        // ```
+        let expanded = value_ty.inner_type().expand_eagerly(self.db());
+        if expanded.is_divergent() {
+            if let Some(builder) = self
+                .context
+                .report_lint(&CYCLIC_TYPE_ALIAS_DEFINITION, type_alias)
+            {
+                builder.into_diagnostic(format_args!(
+                    "Cyclic definition of `{}`",
+                    &type_alias.name.as_name_expr().unwrap().id,
+                ));
+            }
+            // Replace with `Divergent`.
+            self.expressions
+                .insert(type_alias.value.as_ref().into(), expanded);
+        }
     }
 
     /// If the current scope is a method inside an enclosing class,
@@ -1974,6 +2018,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                         // `@overload`ed functions without a body in unreachable code.
                         true
                     }
+                    Type::Dynamic(DynamicType::Divergent(_)) => true,
                     _ => false,
                 }
             })
@@ -5978,6 +6023,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 let inferred = infer_definition_types(self.db(), *definition);
                 // Check non-star imports for deprecations
                 if definition.kind(self.db()).as_star_import().is_none() {
+                    // In the initial cycle, `declaration_types()` is empty, so no deprecation check is performed.
                     for ty in inferred.declaration_types() {
                         self.check_deprecated(alias, ty.inner);
                     }
@@ -6957,6 +7003,9 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         expression: &ast::Expr,
         tcx: TypeContext<'db>,
     ) -> Type<'db> {
+        if self.inner_expression_inference_state.is_get() {
+            return self.expression_type(expression);
+        }
         let ty = match expression {
             ast::Expr::NoneLiteral(ast::ExprNoneLiteral {
                 range: _,
@@ -11725,6 +11774,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             typevar_binding_context: _,
             deferred_state: _,
             multi_inference_state: _,
+            inner_expression_inference_state: _,
             called_functions: _,
             index: _,
             region: _,
@@ -11791,6 +11841,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             typevar_binding_context: _,
             deferred_state: _,
             multi_inference_state: _,
+            inner_expression_inference_state: _,
             called_functions: _,
             index: _,
             region: _,
@@ -11867,6 +11918,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
             typevar_binding_context: _,
             deferred_state: _,
             multi_inference_state: _,
+            inner_expression_inference_state: _,
             called_functions: _,
             index: _,
             region: _,
@@ -11941,6 +11993,19 @@ impl MultiInferenceState {
     }
 }
 
+#[derive(Default, Debug, Clone, Copy)]
+enum InnerExpressionInferenceState {
+    #[default]
+    Infer,
+    Get,
+}
+
+impl InnerExpressionInferenceState {
+    const fn is_get(self) -> bool {
+        matches!(self, InnerExpressionInferenceState::Get)
+    }
+}
+
 /// The deferred state of a specific expression in an inference region.
 #[derive(Default, Debug, Clone, Copy)]
 enum DeferredExpressionState {

crates/ty_python_semantic/src/types/infer/builder/type_expression.rs

@@ -6,20 +6,24 @@ use crate::types::diagnostic::{
     self, INVALID_TYPE_FORM, NON_SUBSCRIPTABLE, report_invalid_argument_number_to_special_form,
     report_invalid_arguments_to_callable,
 };
-use crate::types::signatures::Signature;
+use crate::types::infer::builder::InnerExpressionInferenceState;
+use crate::types::signatures::{Parameter, Parameters, Signature};
 use crate::types::string_annotation::parse_string_annotation;
 use crate::types::tuple::{TupleSpecBuilder, TupleType};
 use crate::types::visitor::any_over_type;
 use crate::types::{
     CallableType, DynamicType, IntersectionBuilder, KnownClass, KnownInstanceType,
-    LintDiagnosticGuard, Parameter, Parameters, SpecialFormType, SubclassOfType, Type,
+    LintDiagnosticGuard, SpecialFormType, SubclassOfType, Type, TypeAliasType, TypeContext,
-    TypeAliasType, TypeContext, TypeIsType, UnionBuilder, UnionType, todo_type,
+    TypeIsType, UnionBuilder, UnionType, todo_type,
 };
 
 /// Type expressions
 impl<'db> TypeInferenceBuilder<'db, '_> {
     /// Infer the type of a type expression.
     pub(super) fn infer_type_expression(&mut self, expression: &ast::Expr) -> Type<'db> {
+        if self.inner_expression_inference_state.is_get() {
+            return self.expression_type(expression);
+        }
         let previous_deferred_state = self.deferred_state;
 
         // `DeferredExpressionState::InStringAnnotation` takes precedence over other states.
@@ -33,13 +37,9 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
             }
             DeferredExpressionState::InStringAnnotation(_) | DeferredExpressionState::Deferred => {}
         }
-        let mut ty = self.infer_type_expression_no_store(expression);
-        self.deferred_state = previous_deferred_state;
 
-        let divergent = Type::divergent(Some(self.scope()));
+        let ty = self.infer_type_expression_no_store(expression);
-        if ty.has_divergent_type(self.db(), divergent) {
+        self.deferred_state = previous_deferred_state;
-            ty = divergent;
-        }
         self.store_expression_type(expression, ty);
         ty
     }
@@ -82,6 +82,9 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
 
     /// Infer the type of a type expression without storing the result.
     pub(super) fn infer_type_expression_no_store(&mut self, expression: &ast::Expr) -> Type<'db> {
+        if self.inner_expression_inference_state.is_get() {
+            return self.expression_type(expression);
+        }
         // https://typing.python.org/en/latest/spec/annotations.html#grammar-token-expression-grammar-type_expression
         match expression {
             ast::Expr::Name(name) => match name.ctx {
@@ -605,7 +608,7 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
                             // TODO: emit a diagnostic
                         }
                     } else {
-                        element_types.push(element_ty.fallback_to_divergent(self.db()));
+                        element_types.push(element_ty);
                     }
                 }
 
@@ -960,6 +963,22 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
                 // For stringified TypeAlias; remove once properly supported
                 todo_type!("string literal subscripted in type expression")
             }
+            Type::Union(union) => {
+                self.infer_type_expression(slice);
+                let previous_slice_inference_state = std::mem::replace(
+                    &mut self.inner_expression_inference_state,
+                    InnerExpressionInferenceState::Get,
+                );
+                let union = union
+                    .elements(self.db())
+                    .iter()
+                    .fold(UnionBuilder::new(self.db()), |builder, elem| {
+                        builder.add(self.infer_subscript_type_expression(subscript, *elem))
+                    })
+                    .build();
+                self.inner_expression_inference_state = previous_slice_inference_state;
+                union
+            }
             _ => {
                 self.infer_type_expression(slice);
                 if let Some(builder) = self.context.report_lint(&INVALID_TYPE_FORM, subscript) {

crates/ty_python_semantic/src/types/instance.rs

@@ -11,7 +11,7 @@ use crate::types::constraints::{ConstraintSet, IteratorConstraintsExtension};
 use crate::types::enums::is_single_member_enum;
 use crate::types::generics::{InferableTypeVars, walk_specialization};
 use crate::types::protocol_class::{ProtocolClass, walk_protocol_interface};
-use crate::types::tuple::{TupleSpec, TupleType};
+use crate::types::tuple::{TupleSpec, TupleType, walk_tuple_type};
 use crate::types::{
     ApplyTypeMappingVisitor, ClassBase, ClassLiteral, FindLegacyTypeVarsVisitor,
     HasRelationToVisitor, IsDisjointVisitor, IsEquivalentVisitor, NormalizedVisitor, TypeContext,
@@ -76,10 +76,7 @@ impl<'db> Type<'db> {
     {
         Type::tuple(TupleType::heterogeneous(
             db,
-            elements
+            elements.into_iter().map(Into::into),
-                .into_iter()
-                .map(Into::into)
-                .map(|element| element.fallback_to_divergent(db)),
         ))
     }
 
@@ -207,7 +204,15 @@ pub(super) fn walk_nominal_instance_type<'db, V: super::visitor::TypeVisitor<'db
     nominal: NominalInstanceType<'db>,
     visitor: &V,
 ) {
-    visitor.visit_type(db, nominal.class(db).into());
+    match nominal.0 {
+        NominalInstanceInner::ExactTuple(tuple) => {
+            walk_tuple_type(db, tuple, visitor);
+        }
+        NominalInstanceInner::Object => {}
+        NominalInstanceInner::NonTuple(class) => {
+            visitor.visit_type(db, class.into());
+        }
+    }
 }
 
 impl<'db> NominalInstanceType<'db> {
@@ -369,6 +374,26 @@ impl<'db> NominalInstanceType<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        match self.0 {
+            NominalInstanceInner::ExactTuple(tuple) => {
+                Some(Self(NominalInstanceInner::ExactTuple(
+                    tuple.recursive_type_normalized_impl(db, div, nested, visitor)?,
+                )))
+            }
+            NominalInstanceInner::NonTuple(class) => Some(Self(NominalInstanceInner::NonTuple(
+                class.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            ))),
+            NominalInstanceInner::Object => Some(Self(NominalInstanceInner::Object)),
+        }
+    }
+
     pub(super) fn has_relation_to_impl(
         self,
         db: &'db dyn Db,
@@ -720,6 +745,21 @@ impl<'db> ProtocolInstanceType<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self {
+            inner: self
+                .inner
+                .recursive_type_normalized_impl(db, div, nested, visitor)?,
+            _phantom: PhantomData,
+        })
+    }
+
     /// Return `true` if this protocol type is equivalent to the protocol `other`.
     ///
     /// TODO: consider the types of the members as well as their existence
@@ -831,6 +871,23 @@ impl<'db> Protocol<'db> {
             Self::Synthesized(synthesized) => synthesized.interface(),
         }
     }
+
+    fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        match self {
+            Self::FromClass(class) => Some(Self::FromClass(
+                class.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+            Self::Synthesized(synthesized) => Some(Self::Synthesized(
+                synthesized.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+        }
+    }
 }
 
 impl<'db> VarianceInferable<'db> for Protocol<'db> {
@@ -849,7 +906,7 @@ mod synthesized_protocol {
     use crate::types::protocol_class::ProtocolInterface;
     use crate::types::{
         ApplyTypeMappingVisitor, BoundTypeVarInstance, FindLegacyTypeVarsVisitor,
-        NormalizedVisitor, TypeContext, TypeMapping, TypeVarVariance, VarianceInferable,
+        NormalizedVisitor, Type, TypeContext, TypeMapping, TypeVarVariance, VarianceInferable,
     };
     use crate::{Db, FxOrderSet};
 
@@ -900,6 +957,19 @@ mod synthesized_protocol {
         pub(in crate::types) fn interface(self) -> ProtocolInterface<'db> {
             self.0
         }
+
+        pub(in crate::types) fn recursive_type_normalized_impl(
+            self,
+            db: &'db dyn Db,
+            div: Type<'db>,
+            nested: bool,
+            visitor: &NormalizedVisitor<'db>,
+        ) -> Option<Self> {
+            Some(Self(
+                self.0
+                    .recursive_type_normalized_impl(db, div, nested, visitor)?,
+            ))
+        }
     }
 
     impl<'db> VarianceInferable<'db> for SynthesizedProtocolType<'db> {

crates/ty_python_semantic/src/types/member.rs

@@ -8,7 +8,7 @@ use crate::types::Type;
 
 /// The return type of certain member-lookup operations. Contains information
 /// about the type, type qualifiers, boundness/declaredness.
-#[derive(Debug, Clone, PartialEq, Eq, salsa::Update, get_size2::GetSize, Default)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, salsa::Update, get_size2::GetSize, Default)]
 pub(super) struct Member<'db> {
     /// Type, qualifiers, and boundness information of this member
     pub(super) inner: PlaceAndQualifiers<'db>,

crates/ty_python_semantic/src/types/newtype.rs

@@ -141,11 +141,11 @@ impl<'db> NewType<'db> {
     /// Create a new `NewType` by mapping the underlying `ClassType`. This descends through any
     /// number of nested `NewType` layers and rebuilds the whole chain. In the rare case of cyclic
     /// `NewType`s with no underlying `ClassType`, this has no effect and does not call `f`.
-    pub(crate) fn map_base_class_type(
+    pub(crate) fn try_map_base_class_type(
         self,
         db: &'db dyn Db,
-        f: impl FnOnce(ClassType<'db>) -> ClassType<'db>,
+        f: impl FnOnce(ClassType<'db>) -> Option<ClassType<'db>>,
-    ) -> Self {
+    ) -> Option<Self> {
         // Modifying the base class type requires unwrapping and re-wrapping however many base
         // newtypes there are between here and there. Normally recursion would be natural for this,
         // but the bases iterator does cycle detection, and I think using that with a stack is a
@@ -162,7 +162,7 @@ impl<'db> NewType<'db> {
                 // We've reached the `ClassType`.
                 NewTypeBase::ClassType(base_class_type) => {
                     // Call `f`.
-                    let mut mapped_base = NewTypeBase::ClassType(f(base_class_type));
+                    let mut mapped_base = NewTypeBase::ClassType(f(base_class_type)?);
                     // Re-wrap the mapped base class in however many newtypes we unwrapped.
                     for inner_newtype in inner_newtype_stack.into_iter().rev() {
                         mapped_base = NewTypeBase::NewType(NewType::new(
@@ -172,18 +172,27 @@ impl<'db> NewType<'db> {
                             Some(mapped_base),
                         ));
                     }
-                    return NewType::new(
+                    return Some(NewType::new(
                         db,
                         self.name(db).clone(),
                         self.definition(db),
                         Some(mapped_base),
-                    );
+                    ));
                 }
             }
         }
         // If we get here, there is no `ClassType` (because this newtype is cyclic), and we don't
         // call `f` at all.
-        self
+        Some(self)
+    }
+
+    pub(crate) fn map_base_class_type(
+        self,
+        db: &'db dyn Db,
+        f: impl FnOnce(ClassType<'db>) -> ClassType<'db>,
+    ) -> Self {
+        self.try_map_base_class_type(db, |class_type| Some(f(class_type)))
+            .unwrap()
     }
 }
 

crates/ty_python_semantic/src/types/protocol_class.rs

@@ -144,6 +144,19 @@ impl<'db> ProtocolClass<'db> {
                 .apply_type_mapping_impl(db, type_mapping, tcx, visitor),
         )
     }
+
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self(
+            self.0
+                .recursive_type_normalized_impl(db, div, nested, visitor)?,
+        ))
+    }
 }
 
 impl<'db> Deref for ProtocolClass<'db> {
@@ -365,6 +378,27 @@ impl<'db> ProtocolInterface<'db> {
         )
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self::new(
+            db,
+            self.inner(db)
+                .iter()
+                .map(|(name, data)| {
+                    Some((
+                        name.clone(),
+                        data.recursive_type_normalized_impl(db, div, nested, visitor)?,
+                    ))
+                })
+                .collect::<Option<BTreeMap<_, _>>>()?,
+        ))
+    }
+
     pub(super) fn specialized_and_normalized<'a>(
         self,
         db: &'db dyn Db,
@@ -456,6 +490,33 @@ impl<'db> ProtocolMemberData<'db> {
         }
     }
 
+    fn recursive_type_normalized_impl(
+        &self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self {
+            kind: match &self.kind {
+                ProtocolMemberKind::Method(callable) => ProtocolMemberKind::Method(
+                    callable.recursive_type_normalized_impl(db, div, nested, visitor)?,
+                ),
+                ProtocolMemberKind::Property(property) => ProtocolMemberKind::Property(
+                    property.recursive_type_normalized_impl(db, div, nested, visitor)?,
+                ),
+                ProtocolMemberKind::Other(ty) if nested => ProtocolMemberKind::Other(
+                    ty.recursive_type_normalized_impl(db, div, true, visitor)?,
+                ),
+                ProtocolMemberKind::Other(ty) => ProtocolMemberKind::Other(
+                    ty.recursive_type_normalized_impl(db, div, true, visitor)
+                        .unwrap_or(div),
+                ),
+            },
+            qualifiers: self.qualifiers,
+        })
+    }
+
     fn apply_type_mapping_impl<'a>(
         &self,
         db: &'db dyn Db,

crates/ty_python_semantic/src/types/signatures.rs

@@ -174,6 +174,22 @@ impl<'db> CallableSignature<'db> {
         )
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        &self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self {
+            overloads: self
+                .overloads
+                .iter()
+                .map(|signature| signature.recursive_type_normalized_impl(db, div, nested, visitor))
+                .collect::<Option<SmallVec<_>>>()?,
+        })
+    }
+
     pub(crate) fn apply_type_mapping_impl<'a>(
         &self,
         db: &'db dyn Db,
@@ -553,6 +569,36 @@ impl<'db> Signature<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        &self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        let return_ty = match self.return_ty {
+            Some(return_ty) if nested => {
+                Some(return_ty.recursive_type_normalized_impl(db, div, true, visitor)?)
+            }
+            Some(return_ty) => Some(
+                return_ty
+                    .recursive_type_normalized_impl(db, div, true, visitor)
+                    .unwrap_or(div),
+            ),
+            None => None,
+        };
+        Some(Self {
+            generic_context: self.generic_context,
+            definition: self.definition,
+            parameters: self
+                .parameters
+                .iter()
+                .map(|param| param.recursive_type_normalized_impl(db, div, nested, visitor))
+                .collect::<Option<_>>()?,
+            return_ty,
+        })
+    }
+
     pub(crate) fn apply_type_mapping_impl<'a>(
         &self,
         db: &'db dyn Db,
@@ -1853,6 +1899,85 @@ impl<'db> Parameter<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        &self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        let Parameter {
+            annotated_type,
+            inferred_annotation,
+            kind,
+            form,
+        } = self;
+
+        let annotated_type = match annotated_type {
+            Some(ty) if nested => Some(ty.recursive_type_normalized_impl(db, div, true, visitor)?),
+            Some(ty) => Some(
+                ty.recursive_type_normalized_impl(db, div, true, visitor)
+                    .unwrap_or(div),
+            ),
+            None => None,
+        };
+
+        let kind = match kind {
+            ParameterKind::PositionalOnly { name, default_type } => ParameterKind::PositionalOnly {
+                name: name.clone(),
+                default_type: match default_type {
+                    Some(ty) if nested => {
+                        Some(ty.recursive_type_normalized_impl(db, div, true, visitor)?)
+                    }
+                    Some(ty) => Some(
+                        ty.recursive_type_normalized_impl(db, div, true, visitor)
+                            .unwrap_or(div),
+                    ),
+                    None => None,
+                },
+            },
+            ParameterKind::PositionalOrKeyword { name, default_type } => {
+                ParameterKind::PositionalOrKeyword {
+                    name: name.clone(),
+                    default_type: match default_type {
+                        Some(ty) if nested => {
+                            Some(ty.recursive_type_normalized_impl(db, div, true, visitor)?)
+                        }
+                        Some(ty) => Some(
+                            ty.recursive_type_normalized_impl(db, div, true, visitor)
+                                .unwrap_or(div),
+                        ),
+                        None => None,
+                    },
+                }
+            }
+            ParameterKind::KeywordOnly { name, default_type } => ParameterKind::KeywordOnly {
+                name: name.clone(),
+                default_type: match default_type {
+                    Some(ty) if nested => {
+                        Some(ty.recursive_type_normalized_impl(db, div, true, visitor)?)
+                    }
+                    Some(ty) => Some(
+                        ty.recursive_type_normalized_impl(db, div, true, visitor)
+                            .unwrap_or(div),
+                    ),
+                    None => None,
+                },
+            },
+            ParameterKind::Variadic { name } => ParameterKind::Variadic { name: name.clone() },
+            ParameterKind::KeywordVariadic { name } => {
+                ParameterKind::KeywordVariadic { name: name.clone() }
+            }
+        };
+
+        Some(Self {
+            annotated_type,
+            inferred_annotation: *inferred_annotation,
+            kind,
+            form: *form,
+        })
+    }
+
     fn from_node_and_kind(
         db: &'db dyn Db,
         definition: Definition<'db>,

crates/ty_python_semantic/src/types/subclass_of.rs

@@ -194,6 +194,20 @@ impl<'db> SubclassOfType<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self {
+            subclass_of: self
+                .subclass_of
+                .recursive_type_normalized_impl(db, div, nested, visitor)?,
+        })
+    }
+
     pub(crate) fn to_instance(self, db: &'db dyn Db) -> Type<'db> {
         match self.subclass_of {
             SubclassOfInner::Class(class) => Type::instance(db, class),
@@ -234,7 +248,7 @@ impl<'db> VarianceInferable<'db> for SubclassOfType<'db> {
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, salsa::Update, get_size2::GetSize)]
 pub(crate) enum SubclassOfInner<'db> {
     Class(ClassType<'db>),
-    Dynamic(DynamicType<'db>),
+    Dynamic(DynamicType),
 }
 
 impl<'db> SubclassOfInner<'db> {
@@ -253,7 +267,7 @@ impl<'db> SubclassOfInner<'db> {
         }
     }
 
-    pub(crate) const fn into_dynamic(self) -> Option<DynamicType<'db>> {
+    pub(crate) const fn into_dynamic(self) -> Option<DynamicType> {
         match self {
             Self::Class(_) => None,
             Self::Dynamic(dynamic) => Some(dynamic),
@@ -267,6 +281,21 @@ impl<'db> SubclassOfInner<'db> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        match self {
+            Self::Class(class) => Some(Self::Class(
+                class.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+            Self::Dynamic(dynamic) => Some(Self::Dynamic(dynamic.recursive_type_normalized())),
+        }
+    }
+
     pub(crate) fn try_from_type(db: &'db dyn Db, ty: Type<'db>) -> Option<Self> {
         match ty {
             Type::Dynamic(dynamic) => Some(Self::Dynamic(dynamic)),
@@ -284,8 +313,8 @@ impl<'db> From<ClassType<'db>> for SubclassOfInner<'db> {
     }
 }
 
-impl<'db> From<DynamicType<'db>> for SubclassOfInner<'db> {
+impl From<DynamicType> for SubclassOfInner<'_> {
-    fn from(value: DynamicType<'db>) -> Self {
+    fn from(value: DynamicType) -> Self {
         SubclassOfInner::Dynamic(value)
     }
 }

crates/ty_python_semantic/src/types/tuple.rs

@@ -229,6 +229,20 @@ impl<'db> TupleType<'db> {
         TupleType::new(db, &self.tuple(db).normalized_impl(db, visitor))
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        Some(Self::new_internal(
+            db,
+            self.tuple(db)
+                .recursive_type_normalized_impl(db, div, nested, visitor)?,
+        ))
+    }
+
     pub(crate) fn apply_type_mapping_impl<'a>(
         self,
         db: &'db dyn Db,
@@ -292,7 +306,7 @@ impl<'db> TupleType<'db> {
 
 fn to_class_type_cycle_initial<'db>(
     db: &'db dyn Db,
-    _id: salsa::Id,
+    id: salsa::Id,
     self_: TupleType<'db>,
 ) -> ClassType<'db> {
     let tuple_class = KnownClass::Tuple
@@ -301,7 +315,7 @@ fn to_class_type_cycle_initial<'db>(
 
     tuple_class.apply_specialization(db, |generic_context| {
         if generic_context.variables(db).len() == 1 {
-            generic_context.specialize_tuple(db, Type::Never, self_)
+            generic_context.specialize_tuple(db, Type::divergent(id), self_)
         } else {
             generic_context.default_specialization(db, Some(KnownClass::Tuple))
         }
@@ -392,6 +406,33 @@ impl<'db> FixedLengthTuple<Type<'db>> {
         Self::from_elements(self.0.iter().map(|ty| ty.normalized_impl(db, visitor)))
     }
 
+    fn recursive_type_normalized_impl(
+        &self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        if nested {
+            Some(Self::from_elements(
+                self.0
+                    .iter()
+                    .map(|ty| ty.recursive_type_normalized_impl(db, div, true, visitor))
+                    .collect::<Option<Box<[_]>>>()?,
+            ))
+        } else {
+            Some(Self::from_elements(
+                self.0
+                    .iter()
+                    .map(|ty| {
+                        ty.recursive_type_normalized_impl(db, div, true, visitor)
+                            .unwrap_or(div)
+                    })
+                    .collect::<Box<[_]>>(),
+            ))
+        }
+    }
+
     fn apply_type_mapping_impl<'a>(
         &self,
         db: &'db dyn Db,
@@ -758,6 +799,56 @@ impl<'db> VariableLengthTuple<Type<'db>> {
         })
     }
 
+    fn recursive_type_normalized_impl(
+        &self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        let prefix = if nested {
+            self.prefix
+                .iter()
+                .map(|ty| ty.recursive_type_normalized_impl(db, div, true, visitor))
+                .collect::<Option<Box<_>>>()?
+        } else {
+            self.prefix
+                .iter()
+                .map(|ty| {
+                    ty.recursive_type_normalized_impl(db, div, true, visitor)
+                        .unwrap_or(div)
+                })
+                .collect::<Box<_>>()
+        };
+        let suffix = if nested {
+            self.suffix
+                .iter()
+                .map(|ty| ty.recursive_type_normalized_impl(db, div, true, visitor))
+                .collect::<Option<Box<_>>>()?
+        } else {
+            self.suffix
+                .iter()
+                .map(|ty| {
+                    ty.recursive_type_normalized_impl(db, div, true, visitor)
+                        .unwrap_or(div)
+                })
+                .collect::<Box<_>>()
+        };
+        let variable = if nested {
+            self.variable
+                .recursive_type_normalized_impl(db, div, true, visitor)?
+        } else {
+            self.variable
+                .recursive_type_normalized_impl(db, div, true, visitor)
+                .unwrap_or(div)
+        };
+        Some(Self {
+            prefix,
+            variable,
+            suffix,
+        })
+    }
+
     fn apply_type_mapping_impl<'a>(
         &self,
         db: &'db dyn Db,
@@ -1154,6 +1245,23 @@ impl<'db> Tuple<Type<'db>> {
         }
     }
 
+    pub(super) fn recursive_type_normalized_impl(
+        &self,
+        db: &'db dyn Db,
+        div: Type<'db>,
+        nested: bool,
+        visitor: &NormalizedVisitor<'db>,
+    ) -> Option<Self> {
+        match self {
+            Tuple::Fixed(tuple) => Some(Tuple::Fixed(
+                tuple.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+            Tuple::Variable(tuple) => Some(Tuple::Variable(
+                tuple.recursive_type_normalized_impl(db, div, nested, visitor)?,
+            )),
+        }
+    }
+
     pub(crate) fn apply_type_mapping_impl<'a>(
         &self,
         db: &'db dyn Db,

crates/ty_python_semantic/src/types/type_ordering.rs

@@ -269,9 +269,7 @@ fn dynamic_elements_ordering(left: DynamicType, right: DynamicType) -> Ordering
         (DynamicType::TodoUnpack, _) => Ordering::Less,
         (_, DynamicType::TodoUnpack) => Ordering::Greater,
 
-        (DynamicType::Divergent(left), DynamicType::Divergent(right)) => {
+        (DynamicType::Divergent(left), DynamicType::Divergent(right)) => left.cmp(&right),
-            left.scope.cmp(&right.scope)
-        }
         (DynamicType::Divergent(_), _) => Ordering::Less,
         (_, DynamicType::Divergent(_)) => Ordering::Greater,
     }

crates/ty_python_semantic/src/types/unpacker.rs

@@ -180,10 +180,11 @@ impl<'db, 'ast> Unpacker<'db, 'ast> {
 
     pub(crate) fn finish(mut self) -> UnpackResult<'db> {
         self.targets.shrink_to_fit();
+
         UnpackResult {
             diagnostics: self.context.finish(),
             targets: self.targets,
-            cycle_fallback_type: None,
+            cycle_recovery: None,
         }
     }
 }
@@ -196,7 +197,7 @@ pub(crate) struct UnpackResult<'db> {
     /// The fallback type for missing expressions.
     ///
     /// This is used only when constructing a cycle-recovery `UnpackResult`.
-    cycle_fallback_type: Option<Type<'db>>,
+    cycle_recovery: Option<Type<'db>>,
 }
 
 impl<'db> UnpackResult<'db> {
@@ -222,7 +223,7 @@ impl<'db> UnpackResult<'db> {
         self.targets
             .get(&expr.into())
             .copied()
-            .or(self.cycle_fallback_type)
+            .or(self.cycle_recovery)
     }
 
     /// Returns the diagnostics in this unpacking assignment.
@@ -230,11 +231,25 @@ impl<'db> UnpackResult<'db> {
         &self.diagnostics
     }
 
-    pub(crate) fn cycle_initial(cycle_fallback_type: Type<'db>) -> Self {
+    pub(crate) fn cycle_initial(cycle_recovery: Type<'db>) -> Self {
         Self {
             targets: FxHashMap::default(),
             diagnostics: TypeCheckDiagnostics::default(),
-            cycle_fallback_type: Some(cycle_fallback_type),
+            cycle_recovery: Some(cycle_recovery),
         }
     }
+
+    pub(crate) fn cycle_normalized(
+        mut self,
+        db: &'db dyn Db,
+        previous_cycle_result: &UnpackResult<'db>,
+        cycle: &salsa::Cycle,
+    ) -> Self {
+        for (expr, ty) in &mut self.targets {
+            let previous_ty = previous_cycle_result.expression_type(*expr);
+            *ty = ty.cycle_normalized(db, previous_ty, cycle);
+        }
+
+        self
+    }
 }

crates/ty_python_semantic/src/types/visitor.rs

@@ -1,5 +1,3 @@
-use rustc_hash::FxHashMap;
-
 use crate::{
     Db, FxIndexSet,
     types::{
@@ -19,10 +17,7 @@ use crate::{
         walk_typed_dict_type, walk_typeis_type, walk_union,
     },
 };
-use std::{
+use std::cell::{Cell, RefCell};
-    cell::{Cell, RefCell},
-    collections::hash_map::Entry,
-};
 
 /// A visitor trait that recurses into nested types.
 ///
@@ -330,148 +325,3 @@ pub(super) fn any_over_type<'db>(
     visitor.visit_type(db, ty);
     visitor.found_matching_type.get()
 }
-
-/// Returns the maximum number of layers of generic specializations for a given type.
-///
-/// For example, `int` has a depth of `0`, `list[int]` has a depth of `1`, and `list[set[int]]`
-/// has a depth of `2`. A set-theoretic type like `list[int] | list[list[int]]` has a maximum
-/// depth of `2`.
-fn specialization_depth(db: &dyn Db, ty: Type<'_>) -> usize {
-    #[derive(Debug, Default)]
-    struct SpecializationDepthVisitor<'db> {
-        seen_types: RefCell<FxHashMap<NonAtomicType<'db>, Option<usize>>>,
-        max_depth: Cell<usize>,
-    }
-
-    impl<'db> TypeVisitor<'db> for SpecializationDepthVisitor<'db> {
-        fn should_visit_lazy_type_attributes(&self) -> bool {
-            false
-        }
-
-        fn visit_type(&self, db: &'db dyn Db, ty: Type<'db>) {
-            match TypeKind::from(ty) {
-                TypeKind::Atomic => {
-                    if ty.is_divergent() {
-                        self.max_depth.set(usize::MAX);
-                    }
-                }
-                TypeKind::NonAtomic(non_atomic_type) => {
-                    match self.seen_types.borrow_mut().entry(non_atomic_type) {
-                        Entry::Occupied(cached_depth) => {
-                            self.max_depth
-                                .update(|current| current.max(cached_depth.get().unwrap_or(0)));
-                            return;
-                        }
-                        Entry::Vacant(entry) => {
-                            entry.insert(None);
-                        }
-                    }
-
-                    let self_depth: usize =
-                        matches!(non_atomic_type, NonAtomicType::GenericAlias(_)).into();
-
-                    let previous_max_depth = self.max_depth.replace(0);
-                    walk_non_atomic_type(db, non_atomic_type, self);
-
-                    self.max_depth.update(|max_child_depth| {
-                        previous_max_depth.max(max_child_depth.saturating_add(self_depth))
-                    });
-
-                    self.seen_types
-                        .borrow_mut()
-                        .insert(non_atomic_type, Some(self.max_depth.get()));
-                }
-            }
-        }
-    }
-
-    let visitor = SpecializationDepthVisitor::default();
-    visitor.visit_type(db, ty);
-    visitor.max_depth.get()
-}
-
-pub(super) fn exceeds_max_specialization_depth(db: &dyn Db, ty: Type<'_>) -> bool {
-    // To prevent infinite recursion during type inference for infinite types, we fall back to
-    // `C[Divergent]` once a certain amount of levels of specialization have occurred. For
-    // example:
-    //
-    // ```py
-    // x = 1
-    // while random_bool():
-    //     x = [x]
-    //
-    // reveal_type(x)  # Unknown | Literal[1] | list[Divergent]
-    // ```
-    const MAX_SPECIALIZATION_DEPTH: usize = 10;
-
-    specialization_depth(db, ty) > MAX_SPECIALIZATION_DEPTH
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::{db::tests::setup_db, types::KnownClass};
-
-    #[test]
-    fn test_generics_layering_depth() {
-        let db = setup_db();
-
-        let int = || KnownClass::Int.to_instance(&db);
-        let list = |element| KnownClass::List.to_specialized_instance(&db, [element]);
-        let dict = |key, value| KnownClass::Dict.to_specialized_instance(&db, [key, value]);
-        let set = |element| KnownClass::Set.to_specialized_instance(&db, [element]);
-        let str = || KnownClass::Str.to_instance(&db);
-        let bytes = || KnownClass::Bytes.to_instance(&db);
-
-        let list_of_int = list(int());
-        assert_eq!(specialization_depth(&db, list_of_int), 1);
-
-        let list_of_list_of_int = list(list_of_int);
-        assert_eq!(specialization_depth(&db, list_of_list_of_int), 2);
-
-        let list_of_list_of_list_of_int = list(list_of_list_of_int);
-        assert_eq!(specialization_depth(&db, list_of_list_of_list_of_int), 3);
-
-        assert_eq!(specialization_depth(&db, set(dict(str(), list_of_int))), 3);
-
-        assert_eq!(
-            specialization_depth(
-                &db,
-                UnionType::from_elements(&db, [list_of_list_of_list_of_int, list_of_list_of_int])
-            ),
-            3
-        );
-
-        assert_eq!(
-            specialization_depth(
-                &db,
-                UnionType::from_elements(&db, [list_of_list_of_int, list_of_list_of_list_of_int])
-            ),
-            3
-        );
-
-        assert_eq!(
-            specialization_depth(
-                &db,
-                Type::heterogeneous_tuple(&db, [Type::heterogeneous_tuple(&db, [int()])])
-            ),
-            2
-        );
-
-        assert_eq!(
-            specialization_depth(&db, Type::heterogeneous_tuple(&db, [list_of_int, str()])),
-            2
-        );
-
-        assert_eq!(
-            specialization_depth(
-                &db,
-                list(UnionType::from_elements(
-                    &db,
-                    [list(int()), list(str()), list(bytes())]
-                ))
-            ),
-            2
-        );
-    }
-}

crates/ty_python_semantic/tests/corpus.rs

@@ -169,9 +169,6 @@ fn run_corpus_tests(pattern: &str) -> anyhow::Result<()> {
 /// Whether or not the .py/.pyi version of this file is expected to fail
 #[rustfmt::skip]
 const KNOWN_FAILURES: &[(&str, bool, bool)] = &[
-    // Fails with too-many-cycle-iterations due to a self-referential
-    // type alias, see https://github.com/astral-sh/ty/issues/256
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F401_34.py", true, true),
 ];
 
 #[salsa::db]

crates/ty_server/tests/e2e/snapshots/e2e__commands__debug_command.snap

@@ -35,6 +35,7 @@ Settings: Settings {
         "conflicting-declarations": Error (Default),
         "conflicting-metaclass": Error (Default),
         "cyclic-class-definition": Error (Default),
+        "cyclic-type-alias-definition": Error (Default),
         "deprecated": Warning (Default),
         "duplicate-base": Error (Default),
         "duplicate-kw-only": Error (Default),

ty.schema.json

@@ -373,6 +373,16 @@
             }
           ]
         },
+        "cyclic-type-alias-definition": {
+          "title": "detects cyclic type alias definitions",
+          "description": "## What it does\nChecks for type alias definitions that (directly or mutually) refer to themselves.\n\n## Why is it bad?\nAlthough it is permitted to define a recursive type alias, it is not meaningful\nto have a type alias whose expansion can only result in itself, and is therefore not allowed.\n\n## Examples\n```python\ntype Itself = Itself\n\ntype A = B\ntype B = A\n```",
+          "default": "error",
+          "oneOf": [
+            {
+              "$ref": "#/definitions/Level"
+            }
+          ]
+        },
         "deprecated": {
           "title": "detects uses of deprecated items",
           "description": "## What it does\nChecks for uses of deprecated items\n\n## Why is this bad?\nDeprecated items should no longer be used.\n\n## Examples\n```python\n@warnings.deprecated(\"use new_func instead\")\ndef old_func(): ...\n\nold_func()  # emits [deprecated] diagnostic\n```",