Auto merge of #19325 - m-novikov:tidy-ignore-without-duplicates, r=jdm

Report an errror if a package has duplicates allowed but there are no duplicates

Resolves: #19306

<!-- Please describe your changes on the following line: -->

---
<!-- 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 #19306 (github issue number if applicable).

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

<!-- 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. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/19325)
<!-- Reviewable:end -->

python/tidy/servo_tidy/tidy.py

@@ -339,10 +339,17 @@ def check_lock(file_name, contents):
         packages_by_name.setdefault(package["name"], []).append((package["version"], source))
 
     for (name, packages) in packages_by_name.iteritems():
-        if name in exceptions or len(packages) <= 1:
+        has_duplicates = len(packages) > 1
+        duplicates_allowed = name in exceptions
+
+        if has_duplicates == duplicates_allowed:
             continue
 
-        message = "duplicate versions for package `{}`".format(name)
+        if duplicates_allowed:
+            message = 'duplicates for `{}` are allowed, but only single version found'.format(name)
+        else:
+            message = "duplicate versions for package `{}`".format(name)
+
         packages.sort()
         packages_dependencies = list(find_reverse_dependencies(name, content))
         for version, source in packages:

python/tidy/servo_tidy_tests/test_tidy.py

@@ -233,6 +233,24 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual(msg2, errors.next()[2])
         self.assertNoMoreErrors(errors)
 
+    def test_lock_ignore_without_duplicates(self):
+        tidy.config["ignore"]["packages"] = ["test", "test2", "test3", "test5"]
+        errors = tidy.collect_errors_for_files(iterFile('duplicated_package.lock'), [tidy.check_lock], [], print_text=False)
+
+        msg = (
+            "duplicates for `test2` are allowed, but only single version found"
+            "\n\t\x1b[93mThe following packages depend on version 0.1.0 from 'https://github.com/user/test2':\x1b[0m"
+        )
+        self.assertEqual(msg, errors.next()[2])
+
+        msg2 = (
+            "duplicates for `test5` are allowed, but only single version found"
+            "\n\t\x1b[93mThe following packages depend on version 0.1.0 from 'https://github.com/':\x1b[0m"
+        )
+        self.assertEqual(msg2, errors.next()[2])
+
+        self.assertNoMoreErrors(errors)
+
     def test_lint_runner(self):
         test_path = base_path + 'lints/'
         runner = tidy.LintRunner(only_changed_files=False, progress=False)