[ty] Baseline for subscript assignment diagnostics (#21404)

## Summary

Add (snapshot) tests for subscript assignment diagnostics. This is
mainly intended to establish a baseline before I hope to improve some of
these messages.

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Invalid_key_type_(d3d47de65fb3bad).snap

@@ -0,0 +1,31 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Invalid key type
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | config: dict[str, int] = {}
+2 | config[0] = 3  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Method `__setitem__` of type `bound method dict[str, int].__setitem__(key: str, value: int, /) -> None` cannot be called with a key of type `Literal[0]` and a value of type `Literal[3]` on object of type `dict[str, int]`
+ --> src/mdtest_snippet.py:2:1
+  |
+1 | config: dict[str, int] = {}
+2 | config[0] = 3  # error: [invalid-assignment]
+  | ^^^^^^
+  |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Invalid_key_type_for…_(815dae276e2fd2b7).snap

@@ -0,0 +1,36 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Invalid key type for `TypedDict`
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | from typing import TypedDict
+2 | 
+3 | class Config(TypedDict):
+4 |     retries: int
+5 | 
+6 | def _(config: Config) -> None:
+7 |     config[0] = 3  # error: [invalid-key]
+```
+
+# Diagnostics
+
+```
+error[invalid-key]: Cannot access `Config` with a key of type `Literal[0]`. Only string literals are allowed as keys on TypedDicts.
+ --> src/mdtest_snippet.py:7:12
+  |
+6 | def _(config: Config) -> None:
+7 |     config[0] = 3  # error: [invalid-key]
+  |            ^
+  |
+info: rule `invalid-key` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Invalid_value_type_(f87bd015df018509).snap

@@ -0,0 +1,31 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Invalid value type
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | config: dict[str, int] = {}
+2 | config["retries"] = "three"  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Method `__setitem__` of type `bound method dict[str, int].__setitem__(key: str, value: int, /) -> None` cannot be called with a key of type `Literal["retries"]` and a value of type `Literal["three"]` on object of type `dict[str, int]`
+ --> src/mdtest_snippet.py:2:1
+  |
+1 | config: dict[str, int] = {}
+2 | config["retries"] = "three"  # error: [invalid-assignment]
+  | ^^^^^^
+  |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Invalid_value_type_f…_(155d53762388f9ad).snap

@@ -0,0 +1,48 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Invalid value type for `TypedDict`
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | from typing import TypedDict
+2 | 
+3 | class Config(TypedDict):
+4 |     retries: int
+5 | 
+6 | def _(config: Config) -> None:
+7 |     config["retries"] = "three"  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Invalid assignment to key "retries" with declared type `int` on TypedDict `Config`
+ --> src/mdtest_snippet.py:7:5
+  |
+6 | def _(config: Config) -> None:
+7 |     config["retries"] = "three"  # error: [invalid-assignment]
+  |     ------ ---------    ^^^^^^^ value of type `Literal["three"]`
+  |     |      |
+  |     |      key has declared type `int`
+  |     TypedDict `Config`
+  |
+info: Item declaration
+ --> src/mdtest_snippet.py:4:5
+  |
+3 | class Config(TypedDict):
+4 |     retries: int
+  |     ------------ Item declared here
+5 |
+6 | def _(config: Config) -> None:
+  |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Misspelled_key_for_`…_(7cf0fa634e2a2d59).snap

@@ -0,0 +1,38 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Misspelled key for `TypedDict`
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | from typing import TypedDict
+2 | 
+3 | class Config(TypedDict):
+4 |     retries: int
+5 | 
+6 | def _(config: Config) -> None:
+7 |     config["Retries"] = 30.0  # error: [invalid-key]
+```
+
+# Diagnostics
+
+```
+error[invalid-key]: Invalid key for TypedDict `Config`
+ --> src/mdtest_snippet.py:7:5
+  |
+6 | def _(config: Config) -> None:
+7 |     config["Retries"] = 30.0  # error: [invalid-key]
+  |     ------ ^^^^^^^^^ Unknown key "Retries" - did you mean "retries"?
+  |     |
+  |     TypedDict `Config`
+  |
+info: rule `invalid-key` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_No_`__setitem__`_met…_(468f62a3bdd1d60c).snap

@@ -0,0 +1,35 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - No `__setitem__` method
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | class ReadOnlyDict:
+2 |     def __getitem__(self, key: str) -> int:
+3 |         return 42
+4 | 
+5 | config = ReadOnlyDict()
+6 | config["retries"] = 3  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Cannot assign to object of type `ReadOnlyDict` with no `__setitem__` method
+ --> src/mdtest_snippet.py:6:1
+  |
+5 | config = ReadOnlyDict()
+6 | config["retries"] = 3  # error: [invalid-assignment]
+  | ^^^^^^
+  |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Possibly_missing_`__…_(efd3f0c02e9b89e9).snap

@@ -0,0 +1,31 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Possibly missing `__setitem__` method
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | def _(config: dict[str, int] | None) -> None:
+2 |     config["retries"] = 3  # error: [possibly-missing-implicit-call]
+```
+
+# Diagnostics
+
+```
+warning[possibly-missing-implicit-call]: Method `__setitem__` of type `dict[str, int] | None` may be missing
+ --> src/mdtest_snippet.py:2:5
+  |
+1 | def _(config: dict[str, int] | None) -> None:
+2 |     config["retries"] = 3  # error: [possibly-missing-implicit-call]
+  |     ^^^^^^
+  |
+info: rule `possibly-missing-implicit-call` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Unknown_key_for_all_…_(1c685d9d10678263).snap

@@ -0,0 +1,40 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Unknown key for all elemens of a union
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | from typing import TypedDict
+ 2 | 
+ 3 | class Person(TypedDict):
+ 4 |     name: str
+ 5 | 
+ 6 | class Animal(TypedDict):
+ 7 |     name: str
+ 8 |     legs: int
+ 9 | 
+10 | def _(being: Person | Animal) -> None:
+11 |     being["surname"] = "unknown"  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Method `__setitem__` of type `(key: Literal["name"], value: str, /) -> None` cannot be called with a key of type `Literal["surname"]` and a value of type `Literal["unknown"]` on object of type `Person | Animal`
+  --> src/mdtest_snippet.py:11:5
+   |
+10 | def _(being: Person | Animal) -> None:
+11 |     being["surname"] = "unknown"  # error: [invalid-assignment]
+   |     ^^^^^
+   |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Unknown_key_for_one_…_(b515711c0a451a86).snap

@@ -0,0 +1,40 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Unknown key for one element of a union
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+ 1 | from typing import TypedDict
+ 2 | 
+ 3 | class Person(TypedDict):
+ 4 |     name: str
+ 5 | 
+ 6 | class Animal(TypedDict):
+ 7 |     name: str
+ 8 |     legs: int
+ 9 | 
+10 | def _(being: Person | Animal) -> None:
+11 |     being["legs"] = 4  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Method `__setitem__` of type `(key: Literal["name"], value: str, /) -> None` cannot be called with a key of type `Literal["legs"]` and a value of type `Literal[4]` on object of type `Person | Animal`
+  --> src/mdtest_snippet.py:11:5
+   |
+10 | def _(being: Person | Animal) -> None:
+11 |     being["legs"] = 4  # error: [invalid-assignment]
+   |     ^^^^^
+   |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Wrong_value_type_for…_(57372b65e30392a8).snap

@@ -0,0 +1,31 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Wrong value type for one element of a union
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | def _(config: dict[str, int] | dict[str, str]) -> None:
+2 |     config["retries"] = 3  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Method `__setitem__` of type `(bound method dict[str, int].__setitem__(key: str, value: int, /) -> None) | (bound method dict[str, str].__setitem__(key: str, value: str, /) -> None)` cannot be called with a key of type `Literal["retries"]` and a value of type `Literal[3]` on object of type `dict[str, int] | dict[str, str]`
+ --> src/mdtest_snippet.py:2:5
+  |
+1 | def _(config: dict[str, int] | dict[str, str]) -> None:
+2 |     config["retries"] = 3  # error: [invalid-assignment]
+  |     ^^^^^^
+  |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/snapshots/assignment_diagnosti…_-_Subscript_assignment…_-_Wrong_value_type_for…_(ffe39a3bae68cfe4).snap

@@ -0,0 +1,31 @@
+---
+source: crates/ty_test/src/lib.rs
+expression: snapshot
+---
+---
+mdtest name: assignment_diagnostics.md - Subscript assignment diagnostics - Wrong value type for all elements of a union
+mdtest path: crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md
+---
+
+# Python source files
+
+## mdtest_snippet.py
+
+```
+1 | def _(config: dict[str, int] | dict[str, str]) -> None:
+2 |     config["retries"] = 3.0  # error: [invalid-assignment]
+```
+
+# Diagnostics
+
+```
+error[invalid-assignment]: Method `__setitem__` of type `(bound method dict[str, int].__setitem__(key: str, value: int, /) -> None) | (bound method dict[str, str].__setitem__(key: str, value: str, /) -> None)` cannot be called with a key of type `Literal["retries"]` and a value of type `float` on object of type `dict[str, int] | dict[str, str]`
+ --> src/mdtest_snippet.py:2:5
+  |
+1 | def _(config: dict[str, int] | dict[str, str]) -> None:
+2 |     config["retries"] = 3.0  # error: [invalid-assignment]
+  |     ^^^^^^
+  |
+info: rule `invalid-assignment` is enabled by default
+
+```

crates/ty_python_semantic/resources/mdtest/subscript/assignment_diagnostics.md

@@ -0,0 +1,117 @@
+# Subscript assignment diagnostics
+
+<!-- snapshot-diagnostics -->
+
+## Invalid value type
+
+```py
+config: dict[str, int] = {}
+config["retries"] = "three"  # error: [invalid-assignment]
+```
+
+## Invalid key type
+
+```py
+config: dict[str, int] = {}
+config[0] = 3  # error: [invalid-assignment]
+```
+
+## Invalid value type for `TypedDict`
+
+```py
+from typing import TypedDict
+
+class Config(TypedDict):
+    retries: int
+
+def _(config: Config) -> None:
+    config["retries"] = "three"  # error: [invalid-assignment]
+```
+
+## Invalid key type for `TypedDict`
+
+```py
+from typing import TypedDict
+
+class Config(TypedDict):
+    retries: int
+
+def _(config: Config) -> None:
+    config[0] = 3  # error: [invalid-key]
+```
+
+## Misspelled key for `TypedDict`
+
+```py
+from typing import TypedDict
+
+class Config(TypedDict):
+    retries: int
+
+def _(config: Config) -> None:
+    config["Retries"] = 30.0  # error: [invalid-key]
+```
+
+## No `__setitem__` method
+
+```py
+class ReadOnlyDict:
+    def __getitem__(self, key: str) -> int:
+        return 42
+
+config = ReadOnlyDict()
+config["retries"] = 3  # error: [invalid-assignment]
+```
+
+## Possibly missing `__setitem__` method
+
+```py
+def _(config: dict[str, int] | None) -> None:
+    config["retries"] = 3  # error: [possibly-missing-implicit-call]
+```
+
+## Unknown key for one element of a union
+
+```py
+from typing import TypedDict
+
+class Person(TypedDict):
+    name: str
+
+class Animal(TypedDict):
+    name: str
+    legs: int
+
+def _(being: Person | Animal) -> None:
+    being["legs"] = 4  # error: [invalid-assignment]
+```
+
+## Unknown key for all elemens of a union
+
+```py
+from typing import TypedDict
+
+class Person(TypedDict):
+    name: str
+
+class Animal(TypedDict):
+    name: str
+    legs: int
+
+def _(being: Person | Animal) -> None:
+    being["surname"] = "unknown"  # error: [invalid-assignment]
+```
+
+## Wrong value type for one element of a union
+
+```py
+def _(config: dict[str, int] | dict[str, str]) -> None:
+    config["retries"] = 3  # error: [invalid-assignment]
+```
+
+## Wrong value type for all elements of a union
+
+```py
+def _(config: dict[str, int] | dict[str, str]) -> None:
+    config["retries"] = 3.0  # error: [invalid-assignment]
+```

crates/ty_python_semantic/resources/mdtest/typed_dict.md

@@ -526,10 +526,20 @@ class Person(TypedDict):
     name: str
     age: int | None
 
+class Animal(TypedDict):
+    name: str
+
 NAME_FINAL: Final = "name"
 AGE_FINAL: Final[Literal["age"]] = "age"
 
-def _(person: Person, literal_key: Literal["age"], union_of_keys: Literal["age", "name"], str_key: str, unknown_key: Any) -> None:
+def _(
+    person: Person,
+    being: Person | Animal,
+    literal_key: Literal["age"],
+    union_of_keys: Literal["age", "name"],
+    str_key: str,
+    unknown_key: Any,
+) -> None:
     reveal_type(person["name"])  # revealed: str
     reveal_type(person["age"])  # revealed: int | None
 
@@ -548,18 +558,30 @@ def _(person: Person, literal_key: Literal["age"], union_of_keys: Literal["age",
 
     # No error here:
     reveal_type(person[unknown_key])  # revealed: Unknown
+
+    reveal_type(being["name"])  # revealed: str
+
+    # TODO: A type of `int | None | Unknown` might be better here. The `str` is mixed in
+    # because `Animal.__getitem__` can only return `str`.
+    # error: [invalid-key] "Invalid key for TypedDict `Animal`"
+    reveal_type(being["age"])  # revealed: int | None | str
 ```
 
 ### Writing
 
 ```py
 from typing_extensions import TypedDict, Final, Literal, LiteralString, Any
+from ty_extensions import Intersection
 
 class Person(TypedDict):
     name: str
     surname: str
     age: int | None
 
+class Animal(TypedDict):
+    name: str
+    legs: int
+
 NAME_FINAL: Final = "name"
 AGE_FINAL: Final[Literal["age"]] = "age"
 
@@ -583,6 +605,23 @@ def _(person: Person, union_of_keys: Literal["name", "surname"]):
     # error: [invalid-assignment] "Cannot assign value of type `Literal[1]` to key of type `Literal["name", "surname"]` on TypedDict `Person`"
     person[union_of_keys] = 1
 
+def _(being: Person | Animal):
+    being["name"] = "Being"
+
+    # error: [invalid-assignment] "Method `__setitem__` of type `(Overload[(key: Literal["name"], value: str, /) -> None, (key: Literal["surname"], value: str, /) -> None, (key: Literal["age"], value: int | None, /) -> None]) | (Overload[(key: Literal["name"], value: str, /) -> None, (key: Literal["legs"], value: int, /) -> None])` cannot be called with a key of type `Literal["name"]` and a value of type `Literal[1]` on object of type `Person | Animal`"
+    being["name"] = 1
+
+    # error: [invalid-assignment] "Method `__setitem__` of type `(Overload[(key: Literal["name"], value: str, /) -> None, (key: Literal["surname"], value: str, /) -> None, (key: Literal["age"], value: int | None, /) -> None]) | (Overload[(key: Literal["name"], value: str, /) -> None, (key: Literal["legs"], value: int, /) -> None])` cannot be called with a key of type `Literal["surname"]` and a value of type `Literal["unknown"]` on object of type `Person | Animal`"
+    being["surname"] = "unknown"
+
+def _(centaur: Intersection[Person, Animal]):
+    centaur["name"] = "Chiron"
+    centaur["age"] = 100
+    centaur["legs"] = 4
+
+    # TODO: This should be an `invalid-key` error
+    centaur["unknown"] = "value"
+
 def _(person: Person, union_of_keys: Literal["name", "age"], unknown_value: Any):
     person[union_of_keys] = unknown_value