checkstyle: Add support for checking style on staged changes

This introduces a new command line "--staged" and a new special type of
commit "StagedChanges". It will check the style of changes that are in
the index, so the changes that would be committed by "git commit".

"--staged" was chosen to match with "git diff --staged" command line.
Other valid name could have been "--index" or "--cached". This was
my personal preference, aliases can be added later. Note that we must
not confuse this with working tree changes, as these changes are not
picked by "git commit".

This feature is needed to implement pre-commit hook.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

utils/checkstyle.py

@@ -481,6 +481,21 @@ class Commit:
                               stdout=subprocess.PIPE).stdout.decode('utf-8')
 
 
+class StagedChanges(Commit):
+    def __init__(self):
+        Commit.__init__(self, '')
+
+    def get_info(self):
+        ret = subprocess.run(['git', 'diff', '--staged', '--name-only'],
+                             stdout=subprocess.PIPE).stdout.decode('utf-8')
+        return "Staged changes", ret.splitlines()
+
+    def get_diff(self, top_level, filename):
+        return subprocess.run(['git', 'diff', '--staged', '--',
+                               '%s/%s' % (top_level, filename)],
+                              stdout=subprocess.PIPE).stdout.decode('utf-8')
+
+
 def check_file(top_level, commit, filename):
     # Extract the line numbers touched by the commit.
     diff = commit.get_diff(top_level, filename)
@@ -611,7 +626,9 @@ def main(argv):
     parser = argparse.ArgumentParser()
     parser.add_argument('--formatter', '-f', type=str, choices=['astyle', 'clang-format'],
                         help='Code formatter. Default to clang-format if not specified.')
-    parser.add_argument('revision_range', type=str, default='HEAD', nargs='?',
+    parser.add_argument('--staged', '-s', action='store_true',
+                        help='Include the changes in the index. Defaults to False')
+    parser.add_argument('revision_range', type=str, default=None, nargs='?',
                         help='Revision range (as defined by git rev-parse). Defaults to HEAD if not specified.')
     args = parser.parse_args(argv[1:])
 
@@ -646,7 +663,18 @@ def main(argv):
     if top_level is None:
             return 1
 
-    commits = extract_commits(args.revision_range)
+    commits = []
+    if args.staged:
+        commits.append(StagedChanges())
+
+    # If not --staged
+    if len(commits) == 0:
+        # And no revisions were passed, then default to HEAD
+        if not args.revision_range:
+            args.revision_range = 'HEAD'
+
+    if args.revision_range:
+        commits += extract_commits(args.revision_range)
 
     issues = 0
     for commit in commits: