Auto merge of #11190 - mrmiywj:Root-tidy-checker, r=jdm

add &Root<T> checker

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 #11137  (github issue number if applicable).

Either:
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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

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python/tidy/servo_tidy/tidy.py

@@ -390,6 +390,8 @@ def check_rust(file_name, lines):
             (r": &Vec<", "use &[T] instead of &Vec<T>", no_filter),
             # No benefit over using &str
             (r": &String", "use &str instead of &String", no_filter),
+            # No benefit to using &Root<T>
+            (r": &Root<", "use &T instead of &Root<T>", no_filter),
             (r"^&&", "operators should go at the end of the first line", no_filter),
             (r"\{[A-Za-z0-9_]+\};", "use statement contains braces for single import",
                 lambda match, line: line.startswith('use ')),

python/tidy/servo_tidy_tests/rust_tidy.rs

@@ -36,7 +36,7 @@ impl test {
         }
     }
 
-    fn test_fun2(y : &String, z : &Vec<f32>) -> f32 {
+    fn test_fun2(y : &String, z : &Vec<f32>, r: &Root<isize>) -> f32 {
         let x = true;
         x
             && x;

python/tidy/servo_tidy_tests/test_tidy.py

@@ -74,6 +74,7 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual('extra space before :', errors.next()[2])
         self.assertEqual('use &[T] instead of &Vec<T>', errors.next()[2])
         self.assertEqual('use &str instead of &String', errors.next()[2])
+        self.assertEqual('use &T instead of &Root<T>', errors.next()[2])
         self.assertEqual('operators should go at the end of the first line', errors.next()[2])
         self.assertNoMoreErrors(errors)