servo: Merge #18179 - Automatically verify that derive() lists are alphabetically ordered #… (from davidcl:master); r=jdm

<!-- Please describe your changes on the following line: -->
Automatically verify that derive() lists are alphabetically ordered #18172

---
<!-- 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 #18172 (github issue number if applicable).

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

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- 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: 474369618965569407d127b1e8c481e757cc59d3

servo/python/tidy/servo_tidy/tidy.py

@@ -692,6 +692,19 @@ def check_rust(file_name, lines):
             # we now erase previous entries
             prev_mod = {}
 
+        # derivable traits should be alphabetically ordered
+        if is_attribute:
+            # match the derivable traits filtering out macro expansions
+            match = re.search(r"#\[derive\(([a-zA-Z, ]*)", line)
+            if match:
+                derives = map(lambda w: w.strip(), match.group(1).split(','))
+                # sort, compare and report
+                sorted_derives = sorted(derives)
+                if sorted_derives != derives:
+                    yield(idx + 1, decl_message.format("derivable traits list")
+                              + decl_expected.format(", ".join(sorted_derives))
+                              + decl_found.format(", ".join(derives)))
+
 
 # Avoid flagging <Item=Foo> constructs
 def is_associated_type(match, line):