Another fix to overload resolution

Author: JukkaL

mypy/checkexpr.py

@@ -1399,7 +1399,9 @@ def visit_erased_type(self, t: ErasedType) -> bool:
 
 def is_compatible_overload_arg(actual: Type, formal: Type) -> bool:
     if (isinstance(actual, NoneTyp) or isinstance(actual, AnyType) or
-            isinstance(formal, AnyType) or isinstance(formal, TypeVar)):
+            isinstance(formal, AnyType) or isinstance(formal, TypeVar) or
+            isinstance(formal, Callable)):
+        # These could match anything at runtime.
         return True
     if isinstance(actual, UnionType):
         return any(is_compatible_overload_arg(item, formal)
@@ -1418,4 +1420,5 @@ def is_compatible_overload_arg(actual: Type, formal: Type) -> bool:
             return formal.type in actual.type.mro
         else:
             return False
+    # Fall back to a conservative equality check for the remaining kinds of type.
     return is_same_type(erasetype.erase_type(actual), erasetype.erase_type(formal))

mypy/test/data/pythoneval.test

@@ -919,3 +919,11 @@ map(f, ['x'])
 map(f, [1])
 [out]
 _program.py, line 4: Argument 1 to "map" has incompatible type Function[["str"] -> "str"]; expected Function[["int"] -> "str"]
+
+[case testMapStr]
+import typing
+x = range(3)
+a = list(map(str, x))
+a + 1
+[out]
+_program.py, line 4: Unsupported operand types for + (List[str] and "int")