Fix inference for constrained type variables within unions (#14396)

Fixes #3644

Handling of constrained type variables of function `filter_satisfiable`
of module `constraints` was missing (as was indicated by a removed
ToDo).

mypy/constraints.py

@@ -420,8 +420,12 @@ def filter_satisfiable(option: list[Constraint] | None) -> list[Constraint] | No
  return option
  satisfiable = []
  for c in option:
- # TODO: add similar logic for TypeVar values (also in various other places)?
- if mypy.subtypes.is_subtype(c.target, c.origin_type_var.upper_bound):
+ if isinstance(c.origin_type_var, TypeVarType) and c.origin_type_var.values:
+ if any(
+ mypy.subtypes.is_subtype(c.target, value) for value in c.origin_type_var.values
+ ):
+ satisfiable.append(c)
+ elif mypy.subtypes.is_subtype(c.target, c.origin_type_var.upper_bound):
  satisfiable.append(c)
  if not satisfiable:
  return None

test-data/unit/check-unions.test

@@ -1171,6 +1171,25 @@ def foo(
 foo([1])
 [builtins fixtures/list.pyi]
 
+[case testGenericUnionMemberWithTypeVarConstraints]
+
+from typing import Generic, TypeVar, Union
+
+T = TypeVar('T', str, int)
+
+class C(Generic[T]): ...
+
+def f(s: Union[T, C[T]]) -> T: ...
+
+ci: C[int]
+cs: C[str]
+
+reveal_type(f(1)) # N: Revealed type is "builtins.int"
+reveal_type(f('')) # N: Revealed type is "builtins.str"
+reveal_type(f(ci)) # N: Revealed type is "builtins.int"
+reveal_type(f(cs)) # N: Revealed type is "builtins.str"
+
+
 [case testNestedInstanceTypeAliasUnsimplifiedUnion]
 from typing import TypeVar, Union, Iterator, List, Any
 T = TypeVar("T")