'await' in non-async function is a blocking error (#15384)

Fixes, #15339

mypy/errorcodes.py

@@ -152,7 +152,9 @@ def __hash__(self) -> int:
 TOP_LEVEL_AWAIT: Final = ErrorCode(
     "top-level-await", "Warn about top level await expressions", "General"
 )
-
+AWAIT_NOT_ASYNC: Final = ErrorCode(
+    "await-not-async", 'Warn about "await" outside coroutine ("async def")', "General"
+)
 # These error codes aren't enabled by default.
 NO_UNTYPED_DEF: Final[ErrorCode] = ErrorCode(
     "no-untyped-def", "Check that every function has an annotation", "General"

mypy/semanal.py

@@ -5455,7 +5455,12 @@ def visit_await_expr(self, expr: AwaitExpr) -> None:
             # support top level awaits.
             self.fail('"await" outside function', expr, serious=True, code=codes.TOP_LEVEL_AWAIT)
         elif not self.function_stack[-1].is_coroutine:
-            self.fail('"await" outside coroutine ("async def")', expr, serious=True, blocker=True)
+            self.fail(
+                '"await" outside coroutine ("async def")',
+                expr,
+                serious=True,
+                code=codes.AWAIT_NOT_ASYNC,
+            )
         expr.expr.accept(self)
 
     #

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

@@ -974,7 +974,7 @@ crasher = [await foo(x) for x in [1, 2, 3]]  # E: "await" outside function  [top
 
 def bad() -> None:
     # These are always critical / syntax issues:
-    y = [await foo(x) for x in [1, 2, 3]]  # E: "await" outside coroutine ("async def")
+    y = [await foo(x) for x in [1, 2, 3]]  # E: "await" outside coroutine ("async def")  [await-not-async]
 async def good() -> None:
     y = [await foo(x) for x in [1, 2, 3]]  # OK
 [builtins fixtures/async_await.pyi]