Fix crash in await inside comprehension outside function

mypy/semanal.py

@@ -5163,10 +5163,11 @@ def visit_yield_expr(self, e: YieldExpr) -> None:
             e.expr.accept(self)
 
     def visit_await_expr(self, expr: AwaitExpr) -> None:
-        if not self.is_func_scope():
-            self.fail('"await" outside function', expr)
+        if not self.is_func_scope() or not self.function_stack:
+            # We check both because is_function_scope() returns True inside comprehensions.
+            self.fail('"await" outside function', expr, serious=True, blocker=True)
         elif not self.function_stack[-1].is_coroutine:
-            self.fail('"await" outside coroutine ("async def")', expr)
+            self.fail('"await" outside coroutine ("async def")', expr, serious=True, blocker=True)
         expr.expr.accept(self)
 
     #

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

@@ -943,3 +943,15 @@ async def bar(x: Union[A, B]) -> None:
 
 [builtins fixtures/async_await.pyi]
 [typing fixtures/typing-async.pyi]
+
+[case testInvalidComprehensionNoCrash]
+async def foo(x: int) -> int: ...
+
+crasher = [await foo(x) for x in [1, 2, 3]]  # E: "await" outside function
+
+def bad() -> None:
+    y = [await foo(x) for x in [1, 2, 3]]  # E: "await" outside coroutine ("async def")
+async def good() -> None:
+    y = [await foo(x) for x in [1, 2, 3]]  # OK
+[builtins fixtures/async_await.pyi]
+[typing fixtures/typing-async.pyi]