Auto merge of #13986 - iamrohit7:tidy-feature-attrs, r=Wafflespeanut

Make test-tidy check for alphabetical ordering of #![feature(...)] statements

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<!-- 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 #13954  (github issue number if applicable).

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

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6 files changed, 51 insertions, 3 deletions

diff --git a/components/net/lib.rs b/components/net/lib.rs
index 822c2105c6e..4ca85975344 100644
--- a/components/net/lib.rs
+++ b/components/net/lib.rs
@@ -2,9 +2,9 @@
  * 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(box_syntax)]
 #![feature(custom_attribute)]
 #![feature(custom_derive)]
-#![feature(box_syntax)]
 #![feature(fnbox)]
 #![feature(mpsc_select)]
 #![feature(plugin)]
diff --git a/components/plugins/lib.rs b/components/plugins/lib.rs
index 30009d63aeb..e62243e8024 100644
--- a/components/plugins/lib.rs
+++ b/components/plugins/lib.rs
@@ -13,7 +13,8 @@
 //!  - `#[dom_struct]` : Implies `#[privatize]`,`#[derive(JSTraceable)]`, and `#[must_root]`.
 //!                       Use this for structs that correspond to a DOM type
 
-#![feature(plugin_registrar, quote, plugin, box_syntax, rustc_private, slice_patterns)]
+
+#![feature(box_syntax, plugin, plugin_registrar, quote, rustc_private, slice_patterns)]
 
 #![deny(unsafe_code)]
 
diff --git a/python/tidy/servo_tidy/tidy.py b/python/tidy/servo_tidy/tidy.py
index b0e420988d7..98eb8fa2d94 100644
--- a/python/tidy/servo_tidy/tidy.py
+++ b/python/tidy/servo_tidy/tidy.py
@@ -385,11 +385,14 @@ def check_rust(file_name, lines):
     import_block = False
     whitespace = False
 
+    is_lib_rs_file = file_name.endswith("lib.rs")
+
     prev_use = None
     prev_open_brace = False
     current_indent = 0
     prev_crate = {}
     prev_mod = {}
+    prev_feature_name = ""
 
     decl_message = "{} is not in alphabetical order"
     decl_expected = "\n\t\033[93mexpected: {}\033[0m"
@@ -517,6 +520,28 @@ def check_rust(file_name, lines):
                       + decl_found.format(crate_name))
             prev_crate[indent] = crate_name
 
+        # check alphabetical order of feature attributes in lib.rs files
+        if is_lib_rs_file:
+            match = re.search(r"#!\[feature\((.*)\)\]", line)
+
+            if match:
+                features = map(lambda w: w.strip(), match.group(1).split(','))
+                sorted_features = sorted(features)
+                if sorted_features != features:
+                    yield(idx + 1, decl_message.format("feature attribute")
+                          + decl_expected.format(tuple(sorted_features))
+                          + decl_found.format(tuple(features)))
+
+                if prev_feature_name > sorted_features[0]:
+                    yield(idx + 1, decl_message.format("feature attribute")
+                          + decl_expected.format(prev_feature_name + " after " + sorted_features[0])
+                          + decl_found.format(prev_feature_name + " before " + sorted_features[0]))
+
+                prev_feature_name = sorted_features[0]
+            else:
+                # not a feature attribute line, so empty previous name
+                prev_feature_name = ""
+
         # imports must be in the same line, alphabetically sorted, and merged
         # into a single import block
         if line.startswith("use "):
diff --git a/python/tidy/servo_tidy_tests/lib.rs b/python/tidy/servo_tidy_tests/lib.rs
new file mode 100644
index 00000000000..4ca395d8e6d
--- /dev/null
+++ b/python/tidy/servo_tidy_tests/lib.rs
@@ -0,0 +1,14 @@
+/* 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(def)]
+#![feature(abc)]
+
+#![feature(abc, def, ghi)]
+#![feature(aaa)]
+
+#![feature(def, ghi, abc)]
+
+#![feature(ghi)]
+#![feature(abd, hef)]
diff --git a/python/tidy/servo_tidy_tests/test_tidy.py b/python/tidy/servo_tidy_tests/test_tidy.py
index 7bec2c61718..d997bb00f82 100644
--- a/python/tidy/servo_tidy_tests/test_tidy.py
+++ b/python/tidy/servo_tidy_tests/test_tidy.py
@@ -127,6 +127,14 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual('extra space after test_fun', errors.next()[2])
         self.assertNoMoreErrors(errors)
 
+        feature_errors = tidy.collect_errors_for_files(iterFile('lib.rs'), [], [tidy.check_rust], print_text=False)
+
+        self.assertTrue('feature attribute is not in alphabetical order' in feature_errors.next()[2])
+        self.assertTrue('feature attribute is not in alphabetical order' in feature_errors.next()[2])
+        self.assertTrue('feature attribute is not in alphabetical order' in feature_errors.next()[2])
+        self.assertTrue('feature attribute is not in alphabetical order' in feature_errors.next()[2])
+        self.assertNoMoreErrors(feature_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)
diff --git a/tests/unit/style/lib.rs b/tests/unit/style/lib.rs
index 164ccadef10..240cac4eb79 100644
--- a/tests/unit/style/lib.rs
+++ b/tests/unit/style/lib.rs
@@ -3,8 +3,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #![cfg(test)]
-#![feature(plugin)]
 #![feature(core_intrinsics)]
+#![feature(plugin)]
 
 extern crate app_units;
 extern crate cssparser;