ClangTidy: Avoid mixing stdout with stderror when dealing with a large number of files.

[Abpostelnicu]

Summary

At Mozilla we are using this tool in order to perform review-time static-analysis, since some patches contain a large number of files we've discovered this issue, where stderr gets mixed with stdout thus obfuscating our possibility to parse the output.
The patch that we are currently use can be found here.

This is just an upstream of the original patch.

[JonasToth]

How does that happen to be a problem? It feels that stdout.write and stderr.write should be unconnected? (if you know the reason I would like to know it too :))
Please note, that run-clang-tidy has an export-feature for the diagnostics and fix-its which might make it easier to analyze the output of clang-tidy.

I suppose you verified the fix already, then LGTM

clang-tidy/tool/run-clang-tidy.py

while True:
 
     proc = subprocess.Popen(invocation, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     output, err = proc.communicate()
     if proc.returncode != 0:
       failed_files.append(name)
     with lock:
       sys.stdout.write(' '.join(invocation) + '\n' + output.decode('utf-8') + '\n')
       if len(err) > 0:
+        sys.stdout.flush()
         sys.stderr.write(err.decode('utf-8') + '\n')
     queue.task_done()
 
 
 def main():
   parser = argparse.ArgumentParser(description='Runs clang-tidy over all files '
                                    'in a compilation database. Requires '
                                    'clang-tidy and clang-apply-replacements in '