Bug 1388721 - [lint] Support --fix in the flake8 linter via autopep8, r=sylvestre

This adds autopep8 to flake8_requirements.txt. When --fix is passed in,
autopep8 will run prior to the normal flake8 run, so only errors that couldn't
be fixed automatically will be shown.

There is one caveat, namely autopep8 will only use the root .flake8 file
(there's no support for passing in subconfigs).

MozReview-Commit-ID: FJ0doey2KVb

tools/lint/python/flake8.py

@@ -6,6 +6,7 @@ import json
 import os
 import platform
 import signal
+import subprocess
 import sys
 from collections import defaultdict
 
@@ -125,6 +126,15 @@ def lint(paths, config, **lintargs):
                     '"column":%(col)s,"rule":"%(code)s","message":"%(text)s"}',
     ]
 
+    fix_cmdargs = [
+        os.path.join(bindir, 'autopep8'),
+        '--global-config', os.path.join(lintargs['root'], '.flake8'),
+        '--in-place', '--recursive',
+    ]
+
+    if 'exclude' in lintargs:
+        fix_cmdargs.extend(['--exclude', ','.join(lintargs['exclude'])])
+
     # Run any paths with a .flake8 file in the directory separately so
     # it gets picked up. This means only .flake8 files that live in
     # directories that are explicitly included will be considered.
@@ -135,8 +145,10 @@ def lint(paths, config, **lintargs):
         paths_by_config[os.pathsep.join(configs) if configs else 'default'].append(path)
 
     for configs, paths in paths_by_config.items():
-        cmd = cmdargs[:]
+        if lintargs.get('fix'):
+            subprocess.call(fix_cmdargs + paths)
 
+        cmd = cmdargs[:]
         if configs != 'default':
             configs = reversed(configs.split(os.pathsep))
             cmd.extend(['--append-config={}'.format(c) for c in configs])