Automatically verify that derive() lists are alphabetically ordered

python/tidy/servo_tidy/tidy.py

@@ -691,6 +691,19 @@ 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):

python/tidy/servo_tidy_tests/rust_tidy.rs

@@ -21,6 +21,7 @@ extern crate webrender_api;
 extern crate style_traits;
 
 #[foo = "bar,baz"]
+#[derive(Copy,Debug, ComputeSquaredDistance)]
 impl test {
 
     fn test_fun(y:f32)->f32{

python/tidy/servo_tidy_tests/test_tidy.py

@@ -107,6 +107,7 @@ class CheckTidiness(unittest.TestCase):
         self.assertTrue('mod declaration is not in alphabetical order' in errors.next()[2])
         self.assertEqual('mod declaration spans multiple lines', errors.next()[2])
         self.assertTrue('extern crate declaration is not in alphabetical order' in errors.next()[2])
+        self.assertTrue('derivable traits list is not in alphabetical order' in errors.next()[2])
         self.assertEqual('found an empty line following a {', errors.next()[2])
         self.assertEqual('missing space before ->', errors.next()[2])
         self.assertEqual('missing space after ->', errors.next()[2])