Adds in_checked_function() to semanal similar to the one in checker (…

…#11156)

Refs #11155

mypy/checkexpr.py

@@ -3506,6 +3506,9 @@ def visit_lambda_expr(self, e: LambdaExpr) -> Type:
             # Type check everything in the body except for the final return
             # statement (it can contain tuple unpacking before return).
             with self.chk.scope.push_function(e):
+                # Lambdas can have more than one element in body,
+                # when we add "fictional" AssigmentStatement nodes, like in:
+                # `lambda (a, b): a`
                 for stmt in e.body.body[:-1]:
                     stmt.accept(self.chk)
                 # Only type check the return expression, not the return statement.

mypy/semanal.py

@@ -4953,17 +4953,26 @@ def is_local_name(self, name: str) -> bool:
         """Does name look like reference to a definition in the current module?"""
         return self.is_defined_in_current_module(name) or '.' not in name
 
+    def in_checked_function(self) -> bool:
+        """Should we type-check the current function?
+
+        - Yes if --check-untyped-defs is set.
+        - Yes outside functions.
+        - Yes in annotated functions.
+        - No otherwise.
+        """
+        return (self.options.check_untyped_defs
+                or not self.function_stack
+                or not self.function_stack[-1].is_dynamic())
+
     def fail(self,
              msg: str,
              ctx: Context,
              serious: bool = False,
              *,
              code: Optional[ErrorCode] = None,
              blocker: bool = False) -> None:
-        if (not serious and
-                not self.options.check_untyped_defs and
-                self.function_stack and
-                self.function_stack[-1].is_dynamic()):
+        if not serious and not self.in_checked_function():
             return
         # In case it's a bug and we don't really have context
         assert ctx is not None, msg
@@ -4973,9 +4982,7 @@ def fail_blocker(self, msg: str, ctx: Context) -> None:
         self.fail(msg, ctx, blocker=True)
 
     def note(self, msg: str, ctx: Context, code: Optional[ErrorCode] = None) -> None:
-        if (not self.options.check_untyped_defs and
-                self.function_stack and
-                self.function_stack[-1].is_dynamic()):
+        if not self.in_checked_function():
             return
         self.errors.report(ctx.get_line(), ctx.get_column(), msg, severity='note', code=code)