## Summary
Add support for implicit type aliases that use PEP 604 unions:
```py
IntOrStr = int | str
reveal_type(IntOrStr) # UnionType
def _(int_or_str: IntOrStr):
reveal_type(int_or_str) # int | str
```
## Typing conformance
The changes are either removed false positives, or new diagnostics due
to known limitations unrelated to this PR.
## Ecosystem impact
Spot checked, a mix of true positives and known limitations.
## Test Plan
New Markdown tests.
This PR introduces a few related changes:
- We now keep track of each time a legacy typevar is bound in a
different generic context (e.g. class, function), and internally create
a new `TypeVarInstance` for each usage. This means the rest of the code
can now assume that salsa-equivalent `TypeVarInstance`s refer to the
same typevar, even taking into account that legacy typevars can be used
more than once.
- We also go ahead and track the binding context of PEP 695 typevars.
That's _much_ easier to track since we have the binding context right
there during type inference.
- With that in place, we can now include the name of the binding context
when rendering typevars (e.g. `T@f` instead of `T`)
## Summary
It doesn't seem to be necessary for our generics implementation to carry
the `GenericContext` in the `ClassBase` variants. Removing it simplifies
the code, fixes many TODOs about `Generic` or `Protocol` appearing
multiple times in MROs when each should only appear at most once, and
allows us to more accurately detect runtime errors that occur due to
`Generic` or `Protocol` appearing multiple times in a class's bases.
In order to remove the `GenericContext` from the `ClassBase` variant, it
turns out to be necessary to emulate
`typing._GenericAlias.__mro_entries__`, or we end up with a large number
of false-positive `inconsistent-mro` errors. This PR therefore also does
that.
Lastly, this PR fixes the inferred MROs of PEP-695 generic classes,
which implicitly inherit from `Generic` even if they have no explicit
bases.
## Test Plan
mdtests
## Summary
Add cycle handling for `try_metaclass` and `pep695_generic_context`
queries, as well as adjusting the cycle handling for `try_mro` to ensure
that it short-circuits on cycles and won't grow MROs indefinitely.
This reduces the number of failing fuzzer seeds from 68 to 17. The
latter count includes fuzzer seeds 120, 160, and 335, all of which
previously panicked but now either hang or are very slow; I've
temporarily skipped those seeds in the fuzzer until I can dig into that
slowness further.
This also allows us to move some more ecosystem projects from `bad.txt`
to `good.txt`, which I've done in
https://github.com/astral-sh/ruff/pull/17903
## Test Plan
Added mdtests.
github-actions[bot]
David Peter
Alex Waygood
Douglas Creager
Carl Meyer
Charlie Marsh
Micha Reiser