metadata: sort discovered files and validation messages

Explicitly sorts the discovered metadata file, and defines
ordering of validation messages, so the tools will output
will be self-consistent.

Change-Id: I9b263a16b151c014e5950638f066376469c701df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5379678
Commit-Queue: Jiewei Qian <qjw@chromium.org>
Reviewed-by: Anne Redulla <aredulla@google.com>

metadata/discover.py

@@ -25,7 +25,7 @@ def find_metadata_files(root: str) -> List[str]:
             search.
 
     Returns: the absolute full paths for all the metadata files within
-             the root directory.
+             the root directory, sorted in ascending order.
     """
     metadata_files = []
 
@@ -35,4 +35,4 @@ def find_metadata_files(root: str) -> List[str]:
                 full_path = os.path.join(root, dirpath, filename)
                 metadata_files.append(full_path)
 
-    return metadata_files
+    return sorted(metadata_files)

metadata/validate.py

@@ -38,7 +38,8 @@ def validate_content(content: str, source_file_dir: str,
         repo_root_dir: the repository's root directory; this is needed
                        to construct file paths to license files.
 
-    Returns: the validation results for the given content.
+    Returns: the validation results for the given content, sorted based
+             severity then message.
     """
     results = []
     dependencies = metadata.parse.parse_content(content)
@@ -50,7 +51,7 @@ def validate_content(content: str, source_file_dir: str,
         dependency_results = dependency.validate(
             source_file_dir=source_file_dir, repo_root_dir=repo_root_dir)
         results.extend(dependency_results)
-    return results
+    return sorted(results)
 
 
 def _construct_file_read_error(filepath: str, cause: str) -> vr.ValidationError:

metadata/validation_result.py

@@ -36,6 +36,33 @@ class ValidationResult:
     def __repr__(self) -> str:
         return str(self)
 
+    # PEP 8 recommends implementing all 6 rich comparisons.
+    # Here we make use of tuple comparison, and order based on the severity
+    # (e.g. fatal comes before non-fatal), then the message.
+    def __lt__(self, other) -> bool:
+        return (not self._fatal, self._message) < (not other._fatal,
+                                                   other._message)
+
+    def __le__(self, other) -> bool:
+        return (not self._fatal, self._message) <= (not other._fatal,
+                                                    other._message)
+
+    def __gt__(self, other) -> bool:
+        return (not self._fatal, self._message) > (not other._fatal,
+                                                   other._message)
+
+    def __ge__(self, other) -> bool:
+        return (not self._fatal, self._message) >= (not other._fatal,
+                                                    other._message)
+
+    def __eq__(self, other) -> bool:
+        return (not self._fatal, self._message) == (not other._fatal,
+                                                    other._message)
+
+    def __ne__(self, other) -> bool:
+        return (not self._fatal, self._message) != (not other._fatal,
+                                                    other._message)
+
     def is_fatal(self) -> bool:
         return self._fatal