From a62caad372de5d2810b1072e4ca23e527f721228 Mon Sep 17 00:00:00 2001
From: Reid Barton <rwbarton@gmail.com>
Date: Mon, 2 May 2016 20:58:28 -0700
Subject: [PATCH] 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                        |  9 ++++++++-
 mypy/test/data/check-typevar-values.test | 14 ++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/mypy/applytype.py b/mypy/applytype.py
index 5d827da4d1a2..29f2287ef39c 100644
--- a/mypy/applytype.py
+++ b/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
diff --git a/mypy/test/data/check-typevar-values.test b/mypy/test/data/check-typevar-values.test
index f9d8223b352a..4f690cdbade3 100644
--- a/mypy/test/data/check-typevar-values.test
+++ b/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])