servo: Merge #15649 - Rewrite the ban-type lint in Python (from zimio:issue-15591-rewrite-ban-type-lint); r=Wafflespeanut

<!-- Please describe your changes on the following line: -->
Rewrite the ban-type lint in Python.

Question: Should the old ban-type lint written in rust be deleted?

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x ] `./mach build -d` does not report any errors
- [x ] `./mach test-tidy` does not report any errors
- [x ] These changes fix #15591

<!-- Either: -->
- [ x] There are tests for these changes

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

Source-Repo: https://github.com/servo/servo
Source-Revision: 261df34ced0bdcb8126994c8653ac101d1172085

servo/python/tidy/servo_tidy_tests/ban-domrefcell.rs

@@ -0,0 +1,19 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#![feature(plugin)]
+#![plugin(script_plugins)]
+
+extern crate script;
+
+use script::test::DOMRefCell;
+use script::test::JS;
+use script::test::Node;
+
+struct Foo {
+    bar: DOMRefCell<JS<Node>>
+    //~^ ERROR Banned type DOMRefCell<JS<T>> detected. Use MutJS<JS<T>> instead
+}
+
+fn main() {}

servo/python/tidy/servo_tidy_tests/ban.rs

@@ -0,0 +1,21 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#![feature(plugin)]
+#![plugin(script_plugins)]
+
+extern crate js;
+
+use js::jsval::JSVal;
+use std::cell::Cell;
+use std::cell::UnsafeCell;
+
+struct Foo {
+    bar: Cell<JSVal>,
+    //~^ ERROR Banned type Cell<JSVal> detected. Use MutJS<JSVal> instead
+    foo: UnsafeCell<JSVal>
+    //~^ NOT AN ERROR
+}
+
+fn main() {}

servo/python/tidy/servo_tidy_tests/test_tidy.py

@@ -140,6 +140,14 @@ class CheckTidiness(unittest.TestCase):
         self.assertTrue('feature attribute is not in alphabetical order' in feature_errors.next()[2])
         self.assertNoMoreErrors(feature_errors)
 
+        ban_errors = tidy.collect_errors_for_files(iterFile('ban.rs'), [], [tidy.check_rust], print_text=False)
+        self.assertEqual('Banned type Cell<JSVal> detected. Use MutJS<JSVal> instead', ban_errors.next()[2])
+        self.assertNoMoreErrors(ban_errors)
+
+        ban_errors = tidy.collect_errors_for_files(iterFile('ban-domrefcell.rs'), [], [tidy.check_rust], print_text=False)
+        self.assertEqual('Banned type DOMRefCell<JS<T>> detected. Use MutJS<JS<T>> instead', ban_errors.next()[2])
+        self.assertNoMoreErrors(ban_errors)
+
     def test_spec_link(self):
         tidy.SPEC_BASE_PATH = base_path
         errors = tidy.collect_errors_for_files(iterFile('speclink.rs'), [], [tidy.check_spec], print_text=False)