disable async/await keywords in nested normal 'def' functions (as CPython does)

Cython/Compiler/Parsing.py

@@ -2039,18 +2039,14 @@ def p_statement(s, ctx, first_statement = 0):
                 return p_async_statement(s, ctx, decorators)
             else:
                 if s.sy == 'IDENT' and s.systring == 'async':
+                    ident_name = s.systring
                     # PEP 492 enables the async/await keywords when it spots "async def ..."
                     s.next()
                     if s.sy == 'def':
-                        s.enable_keyword('async')
-                        s.enable_keyword('await')
-                        result = p_async_statement(s, ctx, decorators)
-                        s.disable_keyword('await')
-                        s.disable_keyword('async')
-                        return result
+                        return p_async_statement(s, ctx, decorators)
                     elif decorators:
                         s.error("Decorators can only be followed by functions or classes")
-                    s.put_back('IDENT', 'async')
+                    s.put_back('IDENT', ident_name)  # re-insert original token
                 return p_simple_statement_list(s, ctx, first_statement=first_statement)
 
 
@@ -3072,7 +3068,25 @@ def p_def_statement(s, decorators=None, is_async_def=False):
     if s.sy == '->':
         s.next()
         return_type_annotation = p_test(s)
+
+    # PEP 492 switches the async/await keywords off in simple "def" functions
+    # and on in "async def" functions
+    await_was_enabled = s.enable_keyword('await') if is_async_def else s.disable_keyword('await')
+    async_was_enabled = s.enable_keyword('async') if is_async_def else s.disable_keyword('async')
+
     doc, body = p_suite_with_docstring(s, Ctx(level='function'))
+
+    if is_async_def:
+        if not async_was_enabled:
+            s.disable_keyword('async')
+        if not await_was_enabled:
+            s.disable_keyword('await')
+    else:
+        if async_was_enabled:
+            s.enable_keyword('async')
+        if await_was_enabled:
+            s.enable_keyword('await')
+
     return Nodes.DefNode(
         pos, name=name, args=args, star_arg=star_arg, starstar_arg=starstar_arg,
         doc=doc, body=body, decorators=decorators, is_async_def=is_async_def,

Cython/Compiler/Scanning.pxd

@@ -30,7 +30,6 @@ cdef class PyrexScanner(Scanner):
     cdef public bint in_python_file
     cdef public source_encoding
     cdef set keywords
-    cdef public dict keywords_stack
     cdef public list indentation_stack
     cdef public indentation_char
     cdef public int bracket_nesting_level
@@ -58,5 +57,5 @@ cdef class PyrexScanner(Scanner):
     cdef expect_indent(self)
     cdef expect_dedent(self)
     cdef expect_newline(self, message=*, bint ignore_semicolon=*)
-    cdef enable_keyword(self, name)
-    cdef disable_keyword(self, name)
+    cdef bint enable_keyword(self, name) except -1
+    cdef bint disable_keyword(self, name) except -1

Cython/Compiler/Scanning.py

@@ -314,7 +314,6 @@ class PyrexScanner(Scanner):
             self.in_python_file = False
             self.keywords = set(pyx_reserved_words)
         self.trace = trace_scanner
-        self.keywords_stack = {}
         self.indentation_stack = [0]
         self.indentation_char = None
         self.bracket_nesting_level = 0
@@ -495,16 +494,13 @@ class PyrexScanner(Scanner):
             warning(useless_trailing_semicolon, "useless trailing semicolon")
 
     def enable_keyword(self, name):
-        if name in self.keywords_stack:
-            self.keywords_stack[name] += 1
-        else:
-            self.keywords_stack[name] = 1
+        if name in self.keywords:
+            return True  # was enabled before
         self.keywords.add(name)
+        return False  # was not enabled before
 
     def disable_keyword(self, name):
-        count = self.keywords_stack.get(name, 1)
-        if count == 1:
-            self.keywords.discard(name)
-            del self.keywords_stack[name]
-        else:
-            self.keywords_stack[name] = count - 1
+        if name not in self.keywords:
+            return False  # was not enabled before
+        self.keywords.remove(name)
+        return True  # was enabled before

tests/run/test_coroutines_pep492.pyx

@@ -138,6 +138,17 @@ class TokenizerRegrTest(unittest.TestCase):
         self.assertEqual(type(ns['foo']()).__name__, 'coroutine')
         #self.assertTrue(inspect.iscoroutinefunction(ns['foo']))
 
+    def test_syntax_async_await_as_names(self):
+        async def enable():
+            await 123
+
+            def disable():
+                await = 123
+                async = 'abc'
+
+                async def reenable():
+                    await 432
+
 
 class CoroutineTest(unittest.TestCase):