Issue #24528: Improve error message for awaits in comprehensions

Lib/test/test_coroutines.py

@@ -106,6 +106,16 @@ class AsyncBadSyntaxTest(unittest.TestCase):
         with self.assertRaisesRegex(SyntaxError, 'invalid syntax'):
             import test.badsyntax_async9
 
+    def test_badsyntax_10(self):
+        ns = {}
+        for comp in {'(await a for a in b)',
+                     '[await a for a in b]',
+                     '{await a for a in b}',
+                     '{await a: c for a in b}'}:
+
+            with self.assertRaisesRegex( SyntaxError, 'await.*in comprehen'):
+                exec('async def f():\n\t{}'.format(comp), ns, ns)
+
 
 class TokenizerRegrTest(unittest.TestCase):
 

Python/compile.c

@@ -3856,7 +3856,10 @@ compiler_visit_expr(struct compiler *c, expr_ty e)
         if (c->u->u_ste->ste_type != FunctionBlock)
             return compiler_error(c, "'await' outside function");
 
-        /* this check won't be triggered while we have AWAIT token */
+        if (c->u->u_scope_type == COMPILER_SCOPE_COMPREHENSION)
+            return compiler_error(
+                c, "'await' expressions in comprehensions are not supported");
+
         if (c->u->u_scope_type != COMPILER_SCOPE_ASYNC_FUNCTION)
             return compiler_error(c, "'await' outside async function");