Allow substituting typevar-with-values for typevar-with-values (#1469)

This is needed for subtyping of generic function with type variables
with values to work correctly, which will be needed for #1261.

mypy/applytype.py

@@ -1,8 +1,9 @@
 from typing import List, Dict
 
 import mypy.subtypes
+from mypy.sametypes import is_same_type
 from mypy.expandtype import expand_type
-from mypy.types import Type, CallableType, AnyType, Void
+from mypy.types import Type, TypeVarType, CallableType, AnyType, Void
 from mypy.messages import MessageBuilder
 from mypy.nodes import Context
 
@@ -29,6 +30,12 @@ def apply_generic_arguments(callable: CallableType, types: List[Type],
  if values and type:
  if isinstance(type, AnyType):
  continue
+ if isinstance(type, TypeVarType) and type.values:
+ # Allow substituting T1 for T if every allowed value of T1
+ # is also a legal value of T.
+ if all(any(is_same_type(v, v1) for v in values)
+ for v1 in type.values):
+ continue
  for value in values:
  if mypy.subtypes.is_subtype(type, value):
  types[i] = value

mypy/test/data/check-typevar-values.test

@@ -465,3 +465,17 @@ def g(x: str) -> str: return x
 main: note: In function "f":
 main:7: error: Incompatible types in assignment (expression has type "object", variable has type "int")
 main:7: error: Incompatible types in assignment (expression has type "object", variable has type "str")
+
+[case testGenericFunctionSubtypingWithTypevarValues]
+from typing import TypeVar
+class A: pass
+T = TypeVar('T', int, str)
+U = TypeVar('U', str, A, int)
+def f(x: T) -> T: pass
+def g(x: U) -> U: pass
+a = f
+a = f
+a = g
+b = g
+b = g
+b = f # E: Incompatible types in assignment (expression has type Callable[[T], T], variable has type Callable[[U], U])