Improve directory mtime support

git-restore-mtime

@@ -294,6 +294,37 @@ def get_mtime_ns(secs: int, idx: int):
 def get_mtime_path(path):
     return os.path.getmtime(path)
 
+class DirectoryMtimes(object):
+    """
+    Track mtimes for path.
+    Lets the newer mtime bubble up to the parent entries.
+    """
+
+    def __init__(self):
+        self.mtimes = {}
+
+    def set_path_mtime(self, path, mtime):
+        """Set mtime of path. Also updates parent paths if mtime is newer."""
+        path_parts = os.path.normpath(path).split(os.sep)
+
+        # Update mtimes for path and parent paths.
+        # Note: '' is a valid path we track an mtime for
+        while True:
+            key = tuple(path_parts)
+            current_mtime = self.mtimes.get(key)
+            if current_mtime is None or current_mtime < mtime:
+                self.mtimes[key] = mtime
+            else:
+                # Assume parent mtimes are already newer
+                break
+
+            if len(path_parts) == 0: break
+            path_parts = path_parts[:-1]
+
+    def get_path_mtime(self, path):
+        """Get mtime recorded for a path"""
+        path_parts = os.path.normpath(path).split(os.sep)
+        return self.mtimes.get(tuple(path_parts))
 
 # Git class and parse_log(), the heart of the script ##########################
 
@@ -366,8 +397,19 @@ class Git:
     class Error(subprocess.CalledProcessError):
         """Error from git executable"""
 
+def touch_dir(dirname, mtime, datestr, stats, git):
+    if args.debug:
+        log.debug("%d\t%d\t-\t%s\t%s",
+                    stats['loglines'], stats['commits'],
+                    datestr, "{}/".format(dirname or '.'))
+    try:
+        touch(os.path.join(git.workdir, dirname), mtime)
+        stats['dirtouches'] += 1
+    except Exception as e:
+        log.error("ERROR: %s: %s", e, dirname)
+        stats['direrrors'] += 1
 
-def parse_log(filelist, dirlist, stats, git, merge=False, filterlist=None):
+def parse_log(filelist, dirlist, dir_times, stats, git, merge=False, filterlist=None):
     mtime = 0
     datestr = isodate(0)
     for line in git.log(
@@ -425,27 +467,20 @@ def parse_log(filelist, dirlist, stats, git, merge=False, filterlist=None):
                 stats['errors'] += 1
 
         def do_dir():
-            if args.debug:
-                log.debug("%d\t%d\t-\t%s\t%s",
-                          stats['loglines'], stats['commits'],
-                          datestr, "{}/".format(dirname or '.'))
-            try:
-                touch(os.path.join(git.workdir, dirname), mtime)
-                stats['dirtouches'] += 1
-            except Exception as e:
-                log.error("ERROR: %s: %s", e, dirname)
-                stats['direrrors'] += 1
+            touch_dir(dirname, mtime, datestr, stats, git)
 
         if file in filelist:
             stats['files'] -= 1
             filelist.remove(file)
             do_file()
+            dir_times.set_path_mtime(file, mtime)
 
         if args.dirs and status in ('A', 'D'):
             dirname = os.path.dirname(file)
             if dirname in dirlist:
                 dirlist.remove(dirname)
                 do_dir()
+                dir_times.set_path_mtime(dirname, mtime)
 
         # All files done?
         if not stats['files']:
@@ -516,7 +551,15 @@ def main():
             filelist -= dirty
 
     # Build dir list to be processed
-    dirlist = set(os.path.dirname(_) for _ in filelist) if args.dirs else set()
+    # For every file name, also add _all_ parent directories to set, so we also consider directories
+    # with just subdirectories, but no files.
+    dirlist = set()
+    if args.dirs:
+        for fn in filelist:
+            current_dir = os.path.dirname(fn)
+            while current_dir != "":
+                dirlist.add(current_dir)
+                current_dir = os.path.dirname(current_dir)
 
     stats['totalfiles'] = stats['files'] = len(filelist)
     log.info("{0:,} files to be processed in work dir".format(stats['totalfiles']))
@@ -525,9 +568,11 @@ def main():
         # Nothing to do. Exit silently and without errors, just like git does
         return
 
+    dir_times = DirectoryMtimes()
+
     # Process the log until all files are 'touched'
     log.debug("Line #\tLog #\tF.Left\tModification Time\tFile Name")
-    parse_log(filelist, dirlist, stats, git, args.merge, args.pathspec)
+    parse_log(filelist, dirlist, dir_times, stats, git, args.merge, args.pathspec)
 
     # Missing files
     if filelist:
@@ -538,13 +583,19 @@ def main():
             missing = len(filterlist)
             log.info("{0:,} files not found in log, trying merge commits".format(missing))
             for i in range(0, missing, STEPMISSING):
-                parse_log(filelist, dirlist, stats, git,
+                parse_log(filelist, dirlist, dir_times, stats, git,
                           merge=True, filterlist=filterlist[i:i + STEPMISSING])
 
         # Still missing some?
         for file in filelist:
             log.warning("WARNING: not found in the log: %s", file)
 
+    # Directories not appearing in log
+    for dir in dirlist:
+        dir_mtime = dir_times.get_path_mtime(dir)
+        if dir_mtime is not None:
+            touch_dir(dir, dir_mtime, isodate(dir_mtime), stats, git)
+
     # Final statistics
     # Suggestion: use git-log --before=mtime to brag about skipped log entries
     def log_info(msg, *a, width=13):