utils: checkstyle.py: Support execution from non-root directories

The git diff command is invoked with relative paths, which causes git to
fail to locate files when the checkstyle.py script is run from
subdirectories of the git tree. Fix this by prepending the absolute path
to the git tree root directory to the file names.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

utils/checkstyle.py

@@ -144,10 +144,11 @@ def parse_diff(diff):
     return hunks
 
 
-def check_file(commit, filename):
+def check_file(top_level, commit, filename):
     # Extract the line numbers touched by the commit.
-    diff = subprocess.run(['git', 'diff', '%s~..%s' % (commit, commit), '--', filename],
-                            stdout=subprocess.PIPE).stdout
+    diff = subprocess.run(['git', 'diff', '%s~..%s' % (commit, commit), '--',
+                           '%s/%s' % (top_level, filename)],
+                          stdout=subprocess.PIPE).stdout
     diff = diff.decode('utf-8').splitlines(True)
     commit_diff = parse_diff(diff)
 
@@ -187,7 +188,7 @@ def check_file(commit, filename):
     return len(formatted_diff)
 
 
-def check_style(commit):
+def check_style(top_level, commit):
     # Get the commit title and list of files.
     ret = subprocess.run(['git', 'show', '--pretty=oneline','--name-only', commit],
                          stdout=subprocess.PIPE)
@@ -208,7 +209,7 @@ def check_style(commit):
 
     issues = 0
     for f in files:
-        issues += check_file(commit, f)
+        issues += check_file(top_level, commit, f)
 
     if issues == 0:
         print("No style issue detected")
@@ -240,6 +241,18 @@ def extract_revlist(revs):
     return revlist
 
 
+def git_top_level():
+    """Get the absolute path of the git top-level directory."""
+    ret = subprocess.run(['git', 'rev-parse', '--show-toplevel'],
+                         stdout=subprocess.PIPE,
+                         stderr=subprocess.PIPE)
+    if ret.returncode != 0:
+        print(ret.stderr.decode('utf-8').splitlines()[0])
+        return None
+
+    return ret.stdout.decode('utf-8').strip()
+
+
 def main(argv):
 
     # Parse command line arguments
@@ -256,12 +269,21 @@ def main(argv):
             print("Executable %s not found" % dependency)
             return 1
 
+    # Get the top level directory to pass absolute file names to git diff
+    # commands, in order to support execution from subdirectories of the git
+    # tree.
+    top_level = git_top_level()
+    if top_level is None:
+            return 1
+
     revlist = extract_revlist(args.revision_range)
 
     for commit in revlist:
-        check_style(commit)
+        check_style(top_level, commit)
         print('')
 
+    return 0
+
 
 if __name__ == '__main__':
     sys.exit(main(sys.argv))