Always respect @no_type_check in two-phase checking (#21320)

This is a somewhat weird, but surprisingly popular edge case.

Author: ilevkivskyi

mypy/checker.py

@@ -701,6 +701,8 @@ def check_partial_impl(self, impl: FuncDef | Decorator) -> None:
         if isinstance(impl, FuncDef):
             self.visit_func_def_impl(impl)
         else:
+            if any(refers_to_fullname(d, "typing.no_type_check") for d in impl.decorators):
+                return
             with self.tscope.function_scope(impl.func):
                 self.check_func_item(impl.func, name=impl.func.name)
 
@@ -5689,12 +5691,10 @@ def visit_del_stmt(self, s: DelStmt) -> None:
                     )
 
     def visit_decorator(self, e: Decorator) -> None:
-        for d in e.decorators:
-            if isinstance(d, RefExpr):
-                if d.fullname == "typing.no_type_check":
-                    e.var.type = AnyType(TypeOfAny.special_form)
-                    e.var.is_ready = True
-                    return
+        if any(refers_to_fullname(d, "typing.no_type_check") for d in e.decorators):
+            e.var.type = AnyType(TypeOfAny.special_form)
+            e.var.is_ready = True
+            return
         self.visit_decorator_inner(e)
 
     def visit_decorator_inner(

test-data/unit/check-functions.test

@@ -1022,6 +1022,14 @@ def foo(x: {1:2}) -> [1]:
     x = y
 [typing fixtures/typing-medium.pyi]
 
+[case testNoTypeCheckDecoratorNoUntypedDefs]
+# flags: --disallow-untyped-defs
+import typing
+
+@typing.no_type_check
+def foo(x: "foo") -> "bar":
+    x: "whatever"
+[typing fixtures/typing-medium.pyi]
 
 -- Forward references to decorated functions
 -- -----------------------------------------