obey no_type_check when inferring params/return

crates/ty_python_semantic/src/types/context.rs

@@ -177,8 +177,8 @@ impl<'db, 'ast> InferContext<'db, 'ast> {
         std::mem::replace(&mut self.multi_inference, multi_inference)
     }
 
-    pub(super) fn set_in_no_type_check(&mut self, no_type_check: InNoTypeCheck) {
+    pub(super) fn set_in_no_type_check(&mut self, no_type_check: InNoTypeCheck) -> InNoTypeCheck {
-        self.no_type_check = no_type_check;
+        std::mem::replace(&mut self.no_type_check, no_type_check)
     }
 
     fn is_in_no_type_check(&self) -> bool {

crates/ty_python_semantic/src/types/infer/builder.rs

@@ -2938,6 +2938,20 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
         definition: Definition<'db>,
         function: &ast::StmtFunctionDef,
     ) {
+        let mut prev_in_no_type_check = self.context.set_in_no_type_check(InNoTypeCheck::Yes);
+        for decorator in &function.decorator_list {
+            let decorator_type = self.infer_decorator(decorator);
+            if let Type::FunctionLiteral(function) = decorator_type
+                && let Some(KnownFunction::NoTypeCheck) = function.known(self.db())
+            {
+                // If the function is decorated with the `no_type_check` decorator,
+                // we need to suppress any errors that come after the decorators.
+                prev_in_no_type_check = InNoTypeCheck::Yes;
+                break;
+            }
+        }
+        self.context.set_in_no_type_check(prev_in_no_type_check);
+
         let previous_typevar_binding_context = self.typevar_binding_context.replace(definition);
         self.infer_return_type_annotation(
             function.returns.as_deref(),