Check Python version before looking up typing.Awaitable.

Ensure 'async def' is a syntax error in Python 2 (at least with the fast parser).

Author: Guido van Rossum

mypy/checker.py

@@ -292,8 +292,12 @@ def is_generator_return_type(self, typ: Type) -> bool:
         True if either Generator or Awaitable is a supertype of `typ`.
         """
         gt = self.named_generic_type('typing.Generator', [AnyType(), AnyType(), AnyType()])
+        if is_subtype(gt, typ):
+            return True
+        if self.options.python_version < (3, 5):
+            return False
         at = self.named_generic_type('typing.Awaitable', [AnyType()])
-        return is_subtype(gt, typ) or is_subtype(at, typ)
+        return is_subtype(at, typ)
 
     def get_generator_yield_type(self, return_type: Type) -> Type:
         """Given the declared return type of a generator (t), return the type it yields (ty)."""

test-data/unit/check-async-await.test

@@ -109,3 +109,8 @@ main: note: In function "f":
 main:3: error: 'yield from' in async function
 main: note: In function "g":
 main:5: error: 'yield from' in async function
+
+[case testNoAsyncDefInPY2_python2]
+# options: fast_parser
+async def f():  # E: invalid syntax
+    pass

test-data/unit/python2eval.test

@@ -440,3 +440,11 @@ re.subn(upat, u'', u'')[0] + u''
 re.subn(ure, lambda m: u'', u'')[0] + u''
 re.subn(upat, lambda m: u'', u'')[0] + u''
 [out]
+
+[case testYieldRegressionTypingAwaitable_python2]
+# Make sure we don't reference typing.Awaitable in Python 2 mode.
+def g() -> int:
+    yield
+[out]
+_program.py: note: In function "g":
+_program.py:2: error: The return type of a generator function should be "Generator" or one of its supertypes