Create TypeVarInstance type for legacy typevars

crates/red_knot_python_semantic/resources/mdtest/function/return_type.md

@@ -203,7 +203,7 @@ from typing import TypeVar
 
 T = TypeVar("T")
 
-# TODO: `invalid-return-type` error should be emitted
+# error: [invalid-return-type]
 def m(x: T) -> T: ...
 ```
 

crates/red_knot_python_semantic/resources/mdtest/generics/legacy.md

@@ -19,6 +19,9 @@ in newer Python releases.
 from typing import TypeVar
 
 T = TypeVar("T")
+reveal_type(type(T))  # revealed: Literal[TypeVar]
+reveal_type(T)  # revealed: typing.TypeVar
+reveal_type(T.__name__)  # revealed: Literal["T"]
 ```
 
 ### Directly assigned to a variable
@@ -29,7 +32,7 @@ T = TypeVar("T")
 ```py
 from typing import TypeVar
 
-# TODO: error
+# error: [invalid-legacy-type-variable] "A legacy `typing.TypeVar` must be immediately assigned to a variable"
 TestList = list[TypeVar("W")]
 ```
 
@@ -40,7 +43,7 @@ TestList = list[TypeVar("W")]
 ```py
 from typing import TypeVar
 
-# TODO: error
+# error: [invalid-legacy-type-variable] "The name of a legacy `typing.TypeVar` must match the name of the variable it is assigned to"
 T = TypeVar("Q")
 ```
 
@@ -57,6 +60,52 @@ T = TypeVar("T")
 T = TypeVar("T")
 ```
 
+### Type variables with a default
+
+Note that the `__default__` property is only available in Python ≥3.13.
+
+```toml
+[environment]
+python-version = "3.13"
+```
+
+```py
+from typing import TypeVar
+
+T = TypeVar("T", default=int)
+reveal_type(T.__default__)  # revealed: int
+reveal_type(T.__bound__)  # revealed: None
+reveal_type(T.__constraints__)  # revealed: tuple[()]
+
+S = TypeVar("S")
+reveal_type(S.__default__)  # revealed: NoDefault
+```
+
+### Type variables with an upper bound
+
+```py
+from typing import TypeVar
+
+T = TypeVar("T", bound=int)
+reveal_type(T.__bound__)  # revealed: int
+reveal_type(T.__constraints__)  # revealed: tuple[()]
+
+S = TypeVar("S")
+reveal_type(S.__bound__)  # revealed: None
+```
+
+### Type variables with constraints
+
+```py
+from typing import TypeVar
+
+T = TypeVar("T", int, str)
+reveal_type(T.__constraints__)  # revealed: tuple[int, str]
+
+S = TypeVar("S")
+reveal_type(S.__constraints__)  # revealed: tuple[()]
+```
+
 ### Cannot have only one constraint
 
 > `TypeVar` supports constraining parametric types to a fixed set of possible types...There should

crates/red_knot_python_semantic/resources/mdtest/generics/pep695.md

@@ -17,10 +17,51 @@ instances of `typing.TypeVar`, just like legacy type variables.
 ```py
 def f[T]():
     reveal_type(type(T))  # revealed: Literal[TypeVar]
-    reveal_type(T)  # revealed: T
+    reveal_type(T)  # revealed: typing.TypeVar
     reveal_type(T.__name__)  # revealed: Literal["T"]
 ```
 
+### Type variables with a default
+
+Note that the `__default__` property is only available in Python ≥3.13.
+
+```toml
+[environment]
+python-version = "3.13"
+```
+
+```py
+def f[T = int]():
+    reveal_type(T.__default__)  # revealed: int
+    reveal_type(T.__bound__)  # revealed: None
+    reveal_type(T.__constraints__)  # revealed: tuple[()]
+
+def g[S]():
+    reveal_type(S.__default__)  # revealed: NoDefault
+```
+
+### Type variables with an upper bound
+
+```py
+def f[T: int]():
+    reveal_type(T.__bound__)  # revealed: int
+    reveal_type(T.__constraints__)  # revealed: tuple[()]
+
+def g[S]():
+    reveal_type(S.__bound__)  # revealed: None
+```
+
+### Type variables with constraints
+
+```py
+def f[T: (int, str)]():
+    reveal_type(T.__constraints__)  # revealed: tuple[int, str]
+    reveal_type(T.__bound__)  # revealed: None
+
+def g[S]():
+    reveal_type(S.__constraints__)  # revealed: tuple[()]
+```
+
 ### Cannot have only one constraint
 
 > `TypeVar` supports constraining parametric types to a fixed set of possible types...There should

crates/red_knot_python_semantic/resources/mdtest/generics/scoping.md

@@ -142,8 +142,7 @@ class Legacy(Generic[T]):
         return y
 
 legacy: Legacy[int] = Legacy()
-# TODO: revealed: str
-reveal_type(legacy.m(1, "string"))  # revealed: @Todo(Support for `typing.TypeVar` instances in type expressions)
+reveal_type(legacy.m(1, "string"))  # revealed: Literal["string"]
 ```
 
 With PEP 695 syntax, it is clearer that the method uses a separate typevar:

crates/red_knot_python_semantic/resources/mdtest/snapshots/return_type.md_-_Function_return_type_-_Invalid_return_type.snap

@@ -28,7 +28,7 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/function/return_ty
 14 | 
 15 | T = TypeVar("T")
 16 | 
-17 | # TODO: `invalid-return-type` error should be emitted
+17 | # error: [invalid-return-type]
 18 | def m(x: T) -> T: ...
 ```
 
@@ -79,3 +79,14 @@ error: lint:invalid-return-type: Return type does not match returned value
    |
 
 ```
+
+```
+error: lint:invalid-return-type: Function can implicitly return `None`, which is not assignable to return type `T`
+  --> /src/mdtest_snippet.py:18:16
+   |
+17 | # error: [invalid-return-type]
+18 | def m(x: T) -> T: ...
+   |                ^
+   |
+
+```

crates/red_knot_python_semantic/resources/mdtest/subscript/lists.md

@@ -12,7 +12,7 @@ x = [1, 2, 3]
 reveal_type(x)  # revealed: list
 
 # TODO reveal int
-reveal_type(x[0])  # revealed: @Todo(Support for `typing.TypeVar` instances in type expressions)
+reveal_type(x[0])  # revealed: Unknown
 
 # TODO reveal list
 reveal_type(x[0:1])  # revealed: @Todo(specialized non-generic class)

crates/red_knot_python_semantic/resources/mdtest/type_properties/is_assignable_to.md

@@ -583,6 +583,8 @@ from functools import partial
 
 def f(x: int, y: str) -> None: ...
 
+# TODO: no error
+# error: [invalid-assignment] "Object of type `partial` is not assignable to `(int, /) -> None`"
 c1: Callable[[int], None] = partial(f, y="a")
 ```