rebaseline_tests.py: Add --new-branch and --clear-cache. NFC (emscripten-core#23192)

Author: sbc100

tools/maint/rebaseline_tests.py

@@ -64,8 +64,13 @@ def process_changed_file(filename):
 def main(argv):
   parser = argparse.ArgumentParser()
   parser.add_argument('-s', '--skip-tests', action='store_true', help="don't actually run the tests, just analyze the existing results")
+  parser.add_argument('-b', '--new-branch', action='store_true', help='create a new branch containing the updates')
+  parser.add_argument('-c', '--clear-cache', action='store_true', help='clear the cache before rebaselining (useful when working with llvm changes)')
   args = parser.parse_args()
 
+  if args.clear_cache:
+    run(['emcc', '--clear-cache'])
+
   if not args.skip_tests:
     if run(['git', 'status', '-uno', '--porcelain']).strip():
       print('tree is not clean')
@@ -91,14 +96,18 @@ def main(argv):
 The following ({len(filenames)}) test expectation files were updated by
 running the tests with `--rebaseline`:
 
+```
 '''
 
   for file in filenames:
     commit_message += process_changed_file(file)
 
   commit_message += f'\nAverage change: {statistics.mean(all_deltas):+.2f}% ({min(all_deltas):+.2f}% - {max(all_deltas):+.2f}%)\n'
 
-  run(['git', 'checkout', '-b', 'rebaseline_tests'])
+  commit_message += '```\n'
+
+  if args.new_branch:
+    run(['git', 'checkout', '-b', 'rebaseline_tests'])
   run(['git', 'add', '-u', '.'])
   run(['git', 'commit', '-F', '-'], input=commit_message)