Allow decorators on nested async-def functions.

Closes https://github.com/cython/cython/issues/1462

CHANGES.rst

@@ -23,6 +23,9 @@ Bugs fixed
 * Complex buffer item types of structs of arrays could fail to validate.
   Patch by Leo and smutch.  (Github issue #1407)
 
+* Decorators were not allowed on nested `async def` functions.
+  (Github issue #1462)
+
 * C-tuples could use invalid C struct casting.
   Patch by MegaIng.  (Github issue #3038)
 

Cython/Compiler/Parsing.py

@@ -2237,7 +2237,7 @@ def p_statement(s, ctx, first_statement = 0):
             s.error('decorator not allowed here')
         s.level = ctx.level
         decorators = p_decorators(s)
-        if not ctx.allow_struct_enum_decorator and s.sy not in ('def', 'cdef', 'cpdef', 'class'):
+        if not ctx.allow_struct_enum_decorator and s.sy not in ('def', 'cdef', 'cpdef', 'class', 'async'):
             if s.sy == 'IDENT' and s.systring == 'async':
                 pass  # handled below
             else:

tests/run/async_def.pyx

@@ -33,3 +33,30 @@ async def test_async_temp_gh3337(x, y):
     ([], 0)
     """
     return min(x - y, 0)
+
+
+async def outer_with_nested(called):
+    """
+    >>> called = []
+    >>> _, inner = run_async(outer_with_nested(called))
+    >>> called  # after outer_with_nested()
+    ['outer', 'make inner', 'deco', 'return inner']
+    >>> _ = run_async(inner())
+    >>> called  # after inner()
+    ['outer', 'make inner', 'deco', 'return inner', 'inner']
+    """
+    called.append('outer')
+
+    def deco(f):
+        called.append('deco')
+        return f
+
+    called.append('make inner')
+
+    @deco
+    async def inner():
+        called.append('inner')
+        return 1
+
+    called.append('return inner')
+    return inner