[ty] Use separate Rust types for bound and unbound type variables (#19796)

This PR creates separate Rust types for bound and unbound type
variables, as proposed in https://github.com/astral-sh/ty/issues/926.

Closes https://github.com/astral-sh/ty/issues/926

---------

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

crates/ty_python_semantic/resources/mdtest/exception/basic.md

@@ -102,7 +102,7 @@ def silence[T: type[BaseException]](
     try:
         func()
     except exception_type as e:
-        reveal_type(e)  # revealed: T'instance
+        reveal_type(e)  # revealed: T'instance@silence
 
 def silence2[T: (
     type[ValueError],
@@ -111,7 +111,7 @@ def silence2[T: (
     try:
         func()
     except exception_type as e:
-        reveal_type(e)  # revealed: T'instance
+        reveal_type(e)  # revealed: T'instance@silence2
 ```
 
 ## Invalid exception handlers

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

@@ -432,3 +432,26 @@ def NamedTemporaryFile(suffix: T | None, prefix: T | None) -> None:
 def f(x: str):
     NamedTemporaryFile(prefix=x, suffix=".tar.gz")  # Fine
 ```
+
+## Nested functions see typevars bound in outer function
+
+```py
+from typing import TypeVar, overload
+
+T = TypeVar("T")
+
+def outer(t: T) -> None:
+    def inner(t: T) -> None: ...
+
+    inner(t)
+
+@overload
+def overloaded_outer() -> None: ...
+@overload
+def overloaded_outer(t: T) -> None: ...
+def overloaded_outer(t: T | None = None) -> None:
+    def inner(t: T) -> None: ...
+
+    if t is not None:
+        inner(t)
+```

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

@@ -20,7 +20,7 @@ from typing import TypeVar
 
 T = TypeVar("T")
 reveal_type(type(T))  # revealed: <class 'TypeVar'>
-reveal_type(T)  # revealed: typing.TypeVar
+reveal_type(T)  # revealed: typing.TypeVar("T")
 reveal_type(T.__name__)  # revealed: Literal["T"]
 ```
 
@@ -79,6 +79,8 @@ python-version = "3.13"
 from typing import TypeVar
 
 T = TypeVar("T", default=int)
+reveal_type(type(T))  # revealed: <class 'TypeVar'>
+reveal_type(T)  # revealed: typing.TypeVar("T", default=int)
 reveal_type(T.__default__)  # revealed: int
 reveal_type(T.__bound__)  # revealed: None
 reveal_type(T.__constraints__)  # revealed: tuple[()]
@@ -113,6 +115,8 @@ class Invalid(Generic[U]): ...
 from typing import TypeVar
 
 T = TypeVar("T", bound=int)
+reveal_type(type(T))  # revealed: <class 'TypeVar'>
+reveal_type(T)  # revealed: typing.TypeVar("T", bound=int)
 reveal_type(T.__bound__)  # revealed: int
 reveal_type(T.__constraints__)  # revealed: tuple[()]
 
@@ -126,6 +130,8 @@ reveal_type(S.__bound__)  # revealed: None
 from typing import TypeVar
 
 T = TypeVar("T", int, str)
+reveal_type(type(T))  # revealed: <class 'TypeVar'>
+reveal_type(T)  # revealed: typing.TypeVar("T", int, str)
 reveal_type(T.__constraints__)  # revealed: tuple[int, str]
 
 S = TypeVar("S")

crates/ty_python_semantic/resources/mdtest/generics/pep695/functions.md

@@ -433,3 +433,24 @@ def f[T: (str, bytes)](suffix: T | None, prefix: T | None):
 def g(x: str):
     f(prefix=x, suffix=".tar.gz")
 ```
+
+## Nested functions see typevars bound in outer function
+
+```py
+from typing import overload
+
+def outer[T](t: T) -> None:
+    def inner[T](t: T) -> None: ...
+
+    inner(t)
+
+@overload
+def overloaded_outer() -> None: ...
+@overload
+def overloaded_outer[T](t: T) -> None: ...
+def overloaded_outer[T](t: T | None = None) -> None:
+    def inner(t: T) -> None: ...
+
+    if t is not None:
+        inner(t)
+```

crates/ty_python_semantic/resources/mdtest/generics/pep695/variables.md

@@ -17,7 +17,7 @@ instances of `typing.TypeVar`, just like legacy type variables.
 ```py
 def f[T]():
     reveal_type(type(T))  # revealed: <class 'TypeVar'>
-    reveal_type(T)  # revealed: typing.TypeVar
+    reveal_type(T)  # revealed: typing.TypeVar("T")
     reveal_type(T.__name__)  # revealed: Literal["T"]
 ```
 
@@ -32,6 +32,8 @@ python-version = "3.13"
 
 ```py
 def f[T = int]():
+    reveal_type(type(T))  # revealed: <class 'TypeVar'>
+    reveal_type(T)  # revealed: typing.TypeVar("T", default=int)
     reveal_type(T.__default__)  # revealed: int
     reveal_type(T.__bound__)  # revealed: None
     reveal_type(T.__constraints__)  # revealed: tuple[()]
@@ -63,6 +65,8 @@ class Invalid[S = T]: ...
 
 ```py
 def f[T: int]():
+    reveal_type(type(T))  # revealed: <class 'TypeVar'>
+    reveal_type(T)  # revealed: typing.TypeVar("T", bound=int)
     reveal_type(T.__bound__)  # revealed: int
     reveal_type(T.__constraints__)  # revealed: tuple[()]
 
@@ -74,6 +78,8 @@ def g[S]():
 
 ```py
 def f[T: (int, str)]():
+    reveal_type(type(T))  # revealed: <class 'TypeVar'>
+    reveal_type(T)  # revealed: typing.TypeVar("T", int, str)
     reveal_type(T.__constraints__)  # revealed: tuple[int, str]
     reveal_type(T.__bound__)  # revealed: None
 

crates/ty_python_semantic/resources/mdtest/type_compendium/never.md

@@ -21,7 +21,9 @@ static_assert(is_subtype_of(Never, Never))
 static_assert(not is_subtype_of(int, Never))
 
 T = TypeVar("T", bound=Never)
-static_assert(is_subtype_of(T, Never))
+
+def _(t: T):
+    static_assert(is_subtype_of(T, Never))
 ```
 
 ## `Never` is assignable to every type