Add missing return type annotation to generators and coroutines.

Closes GH-2884.

CHANGES.rst

@@ -14,6 +14,9 @@ Bugs fixed
 * Casting a GIL-requiring function into a nogil function now issues a warning.
   (Github issue #2879)
 
+* Generators and coroutines were missing their return type annotation.
+  (Github issue #2884)
+
 
 0.29.6 (2019-02-27)
 ===================

Cython/Compiler/ParseTreeTransforms.py

@@ -2624,7 +2624,8 @@ class MarkClosureVisitor(CythonTransform):
             pos=node.pos, name=node.name, args=node.args,
             star_arg=node.star_arg, starstar_arg=node.starstar_arg,
             doc=node.doc, decorators=node.decorators,
-            gbody=gbody, lambda_name=node.lambda_name)
+            gbody=gbody, lambda_name=node.lambda_name,
+            return_type_annotation=node.return_type_annotation)
         return coroutine
 
     def visit_CFuncDefNode(self, node):

tests/run/cython3.pyx

@@ -551,3 +551,11 @@ def annotation_syntax(a: "test new test", b : "other" = 2, *args: "ARGS", **kwar
     result : int = a + b
 
     return result
+
+
+async def async_def_annotations(x: 'int') -> 'float':
+    """
+    >>> sorted(async_def_annotations.__annotations__.items())
+    [('return', 'float'), ('x', 'int')]
+    """
+    return float(x)

tests/run/generators_py35.py

@@ -22,3 +22,14 @@ def with_outer_raising(*args):
             yield i
         raise StopIteration
     return generator
+
+
+def anno_gen(x: 'int') -> 'float':
+    """
+    >>> gen = anno_gen(2)
+    >>> next(gen)
+    2.0
+    >>> sorted(anno_gen.__annotations__.items())
+    [('return', 'float'), ('x', 'int')]
+    """
+    yield float(x)