git-restore-mtime

#!/usr/bin/env python3
#
# git-restore-mtime - Change mtime of files based on commit date of last change
#
#    Copyright (C) 2012 Rodrigo Silva (MestreLion) <linux@rodrigosilva.com>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program. See <http://www.gnu.org/licenses/gpl.html>
#
"""
Change the modification time (mtime) of files in work tree, based on the
date of the most recent commit that modified the file, including renames.

Ignores untracked files and uncommitted deletions, additions and renames, and
by default modifications too.
---
Useful prior to generating release tarballs, so each file is archived with a
date that is similar to the date when the file was actually last modified,
assuming the actual modification date and its commit date are close.
"""

# TODO:
# - Add -z on git whatchanged/ls-files, so we don't deal with filename decoding
# - Update "Statistics for some large projects" with modern hardware and repositories.
# - Create a README.md for git-restore-mtime alone. It deserves extensive documentation
#   - Move Statistics there
# - See git-extras as a good example on project structure and documentation

# FIXME:
# - When current dir is outside the worktree, e.g. using --work-tree, `git ls-files`
#   assume any relative pathspecs are to worktree root, not the current dir. As such,
#   relative pathspecs may not work.
# - Renames are tricky:
#   - R100 should not change mtime, but original name is not on filelist. Should
#     track renames until a valid (A, M) mtime found and then set on current name.
#   - Should set mtime for both current and original directories.
#   - Check mode changes with unchanged blobs?
# - Check file (A, D) for the directory mtime is not sufficient:
#   - Renames also change dir mtime, unless rename was on a parent dir
#   - If most recent change of all files in a dir was a Modification (M),
#     dir might not be touched at all.
#   - Dirs containing only subdirectories but no direct files will also
#     not be touched. They're files' [grand]parent dir, but never their dirname().
#   - Some solutions:
#     - After files done, perform some dir processing for missing dirs, finding latest
#       file (A, D, R)
#     - Simple approach: dir mtime is the most recent child (dir or file) mtime
#     - Use a virtual concept of "created at most at" to fill missing info, bubble up
#       to parents and grandparents
#   - When handling [grand]parent dirs, stay inside <pathspec>
# - Better handling of merge commits. `-m` is plain *wrong*. `-c/--cc` is perfect, but
#   painfully slow. First pass without merge commits is not accurate. Maybe add a new
#   `--accurate` mode for `--cc`?

if __name__ != "__main__":
    raise ImportError("{} should not be used as a module.".format(__name__))

import argparse
import datetime
import logging
import os.path
import shlex
import signal
import subprocess
import sys
import time

if sys.version_info < (3, 8):
    sys.exit("Python 3.8 or later required.")

__version__ = "2022.12+dev"

# Update symlinks only if the platform supports not following them
UPDATE_SYMLINKS = bool(os.utime in getattr(os, 'supports_follow_symlinks', []))

# Call os.path.normpath() only if not in a POSIX platform (Windows)
NORMALIZE_PATHS = (os.path.sep != '/')

# How many files to process in each batch when re-trying merge commits
STEPMISSING = 100

# (Extra) keywords for the os.utime() call performed by touch()
UTIME_KWS = {} if not UPDATE_SYMLINKS else {'follow_symlinks': False}


# Command-line interface ######################################################

def parse_args():
    parser = argparse.ArgumentParser(
        description=__doc__.split('\n---')[0])

    group = parser.add_mutually_exclusive_group()
    group.add_argument('--quiet', '-q', dest='loglevel',
        action="store_const", const=logging.WARNING, default=logging.INFO,
        help="Suppress informative messages and summary statistics.")
    group.add_argument('--verbose', '-v', action="count", help="""
        Print additional information for each processed file.
        Specify twice to further increase verbosity.
        """)

    parser.add_argument('--cwd', '-C', metavar="DIRECTORY", help="""
        Run as if %(prog)s was started in directory %(metavar)s.
        This affects how --work-tree, --git-dir and PATHSPEC arguments are handled.
        See 'man 1 git' or 'git --help' for more information.
        """)

    parser.add_argument('--git-dir', dest='gitdir', metavar="GITDIR", help="""
        Path to the git repository, by default auto-discovered by searching
        the current directory and its parents for a .git/ subdirectory.
        """)

    parser.add_argument('--work-tree', dest='workdir', metavar="WORKTREE", help="""
        Path to the work tree root, by default the parent of GITDIR if it's
        automatically discovered, or the current directory if GITDIR is set.
        """)

    parser.add_argument('--force', '-f', default=False, action="store_true", help="""
        Force updating files with uncommitted modifications.
        Untracked files and uncommitted deletions, renames and additions are
        always ignored.
        """)

    parser.add_argument('--merge', '-m', default=False, action="store_true", help="""
        Include merge commits.
        Leads to more recent times and more files per commit, thus with the same
        time, which may or may not be what you want.
        Including merge commits may lead to fewer commits being evaluated as files
        are found sooner, which can improve performance, sometimes substantially.
        But as merge commits are usually huge, processing them may also take longer.
        By default, merge commits are only used for files missing from regular commits.
        """)

    parser.add_argument('--first-parent', default=False, action="store_true", help="""
        Consider only the first parent, the "main branch", when evaluating merge commits.
        Only effective when merge commits are processed, either when --merge is
        used or when finding missing files after the first regular log search.
        See --skip-missing.
        """)

    parser.add_argument('--skip-missing', '-s', dest="missing", default=True,
        action="store_false", help="""
        Do not try to find missing files.
        If merge commits were not evaluated with --merge and some files were
        not found in regular commits, by default %(prog)s searches for these
        files again in the merge commits.
        This option disables this retry, so files found only in merge commits
        will not have their timestamp updated.
        """)

    parser.add_argument('--no-directories', '-D', dest='dirs', default=True,
        action="store_false", help="""
        Do not update directory timestamps.
        By default, use the time of its most recently created, renamed or deleted file.
        Note that just modifying a file will NOT update its directory time.
        """)

    parser.add_argument('--test', '-t', default=False, action="store_true",
        help="Test run: do not actually update any file timestamp.")

    parser.add_argument('--commit-time', '-c', dest='commit_time', default=False,
        action='store_true', help="Use commit time instead of author time.")

    parser.add_argument('--oldest-time', '-o', dest='reverse_order', default=False,
        action='store_true', help="""
        Update times based on the oldest, instead of the most recent commit of a file.
        This reverses the order in which the git log is processed to emulate a
        file "creation" date. Note this will be inaccurate for files deleted and
        re-created at later dates.
        """)

    parser.add_argument('--skip-older-than', metavar='SECONDS', type=int, help="""
        Ignore files that are currently older than %(metavar)s.
        Useful in workflows that assume such files already have a correct timestamp,
        as it may improve performance by processing fewer files.
        """)

    parser.add_argument('--skip-older-than-commit', '-N', default=False,
        action='store_true', help="""
        Ignore files older than the timestamp it would be updated to.
        Such files may be considered "original", likely in the author's repository.
        """)

    parser.add_argument('--unique-times', default=False, action="store_true", help="""
        Set the microseconds to a unique value per commit.
        Allows telling apart changes that would otherwise have identical timestamps,
        as git's time accuracy is in seconds.
        """)

    parser.add_argument('pathspec', nargs='*', metavar='PATHSPEC', help="""
        Only modify paths matching %(metavar)s, relative to current directory.
        By default, update all but untracked files and submodules.
        """)

    parser.add_argument('--version', '-V', action='version',
        version='%(prog)s version {version}'.format(version=get_version()))

    args_ = parser.parse_args()
    if args_.verbose:
        args_.loglevel = max(logging.TRACE, logging.DEBUG // args_.verbose)
    args_.debug = args_.loglevel <= logging.DEBUG
    return args_


def get_version(version=__version__):
    if not version.endswith('+dev'):
        return version
    try:
        cwd = os.path.dirname(os.path.realpath(__file__))
        return Git(cwd=cwd, errors=False).describe().lstrip('v')
    except Git.Error:
        return '-'.join((version, "unknown"))


# Helper functions ############################################################

def setup_logging():
    """Add TRACE logging level and corresponding method, return the root logger"""
    logging.TRACE = TRACE = logging.DEBUG // 2
    logging.Logger.trace = lambda _, m, *a, **k: _.log(TRACE, m, *a, **k)
    return logging.getLogger()


def normalize(path):
    r"""Normalize paths from git, handling non-ASCII characters.

    Git stores paths as UTF-8 normalization form C.
    If path contains non-ASCII or non-printable characters, git outputs the UTF-8
    in octal-escaped notation, escaping double-quotes and backslashes, and then
    double-quoting the whole path.
    https://git-scm.com/docs/git-config#Documentation/git-config.txt-corequotePath

    This function reverts this encoding, so:
    normalize(r'"Back\\slash_double\"quote_a\303\247a\303\255"') =>
        r'Back\slash_double"quote_açaí')

    Paths with invalid UTF-8 encoding, such as single 0x80-0xFF bytes (e.g, from
    Latin1/Windows-1251 encoding) are decoded using surrogate escape, the same
    method used by Python for filesystem paths. So 0xE6 ("æ" in Latin1, r'\\346'
    from Git) is decoded as "\udce6". See https://peps.python.org/pep-0383/ and
    https://vstinner.github.io/painful-history-python-filesystem-encoding.html

    Also see notes on `windows/non-ascii-paths.txt` about path encodings on
    non-UTF-8 platforms and filesystems.
    """
    if path and path[0] == '"':
        # Python 2: path = path[1:-1].decode("string-escape")
        # Python 3: https://stackoverflow.com/a/46650050/624066
        path = (path[1:-1]                 # Remove enclosing double quotes
                .encode('latin1')          # Convert to bytes, required by 'unicode-escape'
                .decode('unicode-escape')  # Perform the actual octal-escaping decode
                .encode('latin1')          # 1:1 mapping to bytes, UTF-8 encoded
                .decode('utf8', 'surrogateescape'))  # Decode from UTF-8
    if NORMALIZE_PATHS:
        # Make sure the slash matches the OS; for Windows we need a backslash
        path = os.path.normpath(path)
    return path


def dummy(*_args, **_kwargs):
    """No-op function used in dry-run tests"""


def touch(path, mtime):
    """The actual mtime update"""
    os.utime(path, (mtime, mtime), **UTIME_KWS)


def touch_ns(path, mtime_ns):
    """The actual mtime update, using nanoseconds for unique timestamps"""
    os.utime(path, None, ns=(mtime_ns, mtime_ns), **UTIME_KWS)


def isodate(secs: int):
    # time.localtime() accepts floats, but discards fractional part
    return time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(secs))


def isodate_ns(ns: int):
    # for integers fromtimestamp() is equivalent and ~16% slower than isodate()
    return datetime.datetime.fromtimestamp(ns / 1000000000).isoformat(sep=' ')


def get_mtime_ns(secs: int, idx: int):
    # Time resolution for filesystems and functions:
    # ext-4 and other POSIX filesystems: 1 nanosecond
    # NTFS (Windows default): 100 nanoseconds
    # datetime.datetime() (due to 64-bit float epoch): 1 microsecond
    us = idx % 1000000  # 10**6
    return 1000 * (1000000 * secs + us)


def get_mtime_path(path):
    return os.path.getmtime(path)


# Git class and parse_log(), the heart of the script ##########################

class Git:
    def __init__(self, workdir=None, gitdir=None, cwd=None, errors=True):
        self.gitcmd = ['git']
        self.errors = errors
        self._proc = None
        if workdir: self.gitcmd.extend(('--work-tree', workdir))
        if gitdir:  self.gitcmd.extend(('--git-dir',   gitdir))
        if cwd:     self.gitcmd.extend(('-C',          cwd))
        self.workdir, self.gitdir = self._get_repo_dirs()

    def ls_files(self, paths: list = None):
        return (normalize(_) for _ in self._run('ls-files --full-name', paths))

    def ls_dirty(self, force=False):
        return (normalize(_[3:].split(' -> ', 1)[-1])
                for _ in self._run('status --porcelain')
                if _[:2] != '??' and (not force or (_[0] in ('R', 'A')
                                                    or _[1] == 'D')))

    def log(self, merge=False, first_parent=False, commit_time=False,
            reverse_order=False, paths: list = None):
        cmd = 'whatchanged --no-show-signature --pretty={}'.format('%ct' if commit_time else '%at')
        if merge:         cmd += ' -m'
        if first_parent:  cmd += ' --first-parent'
        if reverse_order: cmd += ' --reverse'
        return self._run(cmd, paths)

    def describe(self):
        return self._run('describe --tags', check=True)[0]

    def terminate(self):
        if self._proc is None:
            return
        try:
            self._proc.terminate()
        except OSError:
            # Avoid errors on OpenBSD
            pass

    def _get_repo_dirs(self):
        return (os.path.normpath(_) for _ in
            self._run('rev-parse --show-toplevel --absolute-git-dir', check=True))

    def _run(self, cmdstr: str, paths: list = None, output=True, check=False):
        cmdlist = self.gitcmd + shlex.split(cmdstr)
        if paths:
            cmdlist.append('--')
            cmdlist.extend(paths)
        popen_args = dict(text=True, encoding='utf8')
        if not self.errors:
            popen_args['stderr'] = subprocess.DEVNULL
        log.trace("Executing: %s", ' '.join(cmdlist))
        if not output:
            return subprocess.call(cmdlist, **popen_args)
        if check:
            try:
                stdout: str = subprocess.check_output(cmdlist, **popen_args)
                return stdout.splitlines()
            except subprocess.CalledProcessError as e:
                raise self.Error(e.returncode, e.cmd, e.output, e.stderr)
        self._proc = subprocess.Popen(cmdlist, stdout=subprocess.PIPE, **popen_args)
        return (_.rstrip() for _ in self._proc.stdout)

    def __del__(self):
        self.terminate()

    class Error(subprocess.CalledProcessError):
        """Error from git executable"""


def parse_log(filelist, dirlist, stats, git, merge=False, filterlist=None):
    mtime = 0
    datestr = isodate(0)
    for line in git.log(
            merge,
            args.first_parent,
            args.commit_time,
            args.reverse_order,
            filterlist
    ):
        stats['loglines'] += 1

        # Blank line between Date and list of files
        if not line:
            continue

        # Date line
        if line[0] != ':':  # Faster than `not line.startswith(':')`
            stats['commits'] += 1
            mtime = int(line)
            if args.unique_times:
                mtime = get_mtime_ns(mtime, stats['commits'])
            if args.debug:
                datestr = isodate(mtime)
            continue

        # File line: three tokens if it describes a renaming, otherwise two
        tokens = line.split('\t')

        # Possible statuses:
        # M: Modified (content changed)
        # A: Added (created)
        # D: Deleted
        # T: Type changed: to/from regular file, symlinks, submodules
        # R099: Renamed (moved), with % of unchanged content. 100 = pure rename
        # Not possible in log: C=Copied, U=Unmerged, X=Unknown, B=pairing Broken
        status = tokens[0].split(' ')[-1]
        file = tokens[-1]

        # Handles non-ASCII chars and OS path separator
        file = normalize(file)

        def do_file():
            if args.skip_older_than_commit and get_mtime_path(file) <= mtime:
                stats['skip'] += 1
                return
            if args.debug:
                log.debug("%d\t%d\t%d\t%s\t%s",
                          stats['loglines'], stats['commits'], stats['files'],
                          datestr, file)
            try:
                touch(os.path.join(git.workdir, file), mtime)
                stats['touches'] += 1
            except Exception as e:
                log.error("ERROR: %s: %s", e, file)
                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

        if file in filelist:
            stats['files'] -= 1
            filelist.remove(file)
            do_file()

        if args.dirs and status in ('A', 'D'):
            dirname = os.path.dirname(file)
            if dirname in dirlist:
                dirlist.remove(dirname)
                do_dir()

        # All files done?
        if not stats['files']:
            git.terminate()
            return


# Main Logic ##################################################################

def main():
    start = time.time()  # yes, Wall time. CPU time is not realistic for users.
    stats = {_: 0 for _ in ('loglines', 'commits', 'touches', 'skip', 'errors',
                            'dirtouches', 'direrrors')}

    logging.basicConfig(level=args.loglevel, format='%(message)s')
    log.trace("Arguments: %s", args)

    # First things first: Where and Who are we?
    if args.cwd:
        log.debug("Changing directory: %s", args.cwd)
        try:
            os.chdir(args.cwd)
        except OSError as e:
            log.critical(e)
            return e.errno
    # Using both os.chdir() and `git -C` is redundant, but might prevent side effects
    # `git -C` alone could be enough if we make sure that:
    # - all paths, including args.pathspec, are processed by git: ls-files, rev-parse
    # - touch() / os.utime() path argument is always prepended with git.workdir
    try:
        git = Git(workdir=args.workdir, gitdir=args.gitdir, cwd=args.cwd)
    except Git.Error as e:
        # Not in a git repository, and git already informed user on stderr. So we just...
        return e.returncode

    # Get the files managed by git and build file list to be processed
    if UPDATE_SYMLINKS and not args.skip_older_than:
        filelist = set(git.ls_files(args.pathspec))
    else:
        filelist = set()
        for path in git.ls_files(args.pathspec):
            fullpath = os.path.join(git.workdir, path)

            # Symlink (to file, to dir or broken - git handles the same way)
            if not UPDATE_SYMLINKS and os.path.islink(fullpath):
                log.warning("WARNING: Skipping symlink, no OS support for updates: %s",
                            path)
                continue

            # skip files which are older than given threshold
            if (args.skip_older_than
                    and start - get_mtime_path(fullpath) > args.skip_older_than):
                continue

            # Always add files relative to worktree root
            filelist.add(path)

    # If --force, silently ignore uncommitted deletions (not in the filesystem)
    # and renames / additions (will not be found in log anyway)
    if args.force:
        filelist -= set(git.ls_dirty(force=True))
    # Otherwise, ignore any dirty files
    else:
        dirty = set(git.ls_dirty())
        if dirty:
            log.warning("WARNING: Modified files in the working directory were ignored."
                "\nTo include such files, commit your changes or use --force.")
            filelist -= dirty

    # Build dir list to be processed
    dirlist = set(os.path.dirname(_) for _ in filelist) if args.dirs else set()

    stats['totalfiles'] = stats['files'] = len(filelist)
    log.info("{0:,} files to be processed in work dir".format(stats['totalfiles']))

    if not filelist:
        # Nothing to do. Exit silently and without errors, just like git does
        return

    # 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)

    # Missing files
    if filelist:
        # Try to find them in merge logs, if not done already
        # (usually HUGE, thus MUCH slower!)
        if args.missing and not args.merge:
            filterlist = list(filelist)
            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,
                          merge=True, filterlist=filterlist[i:i + STEPMISSING])

        # Still missing some?
        for file in filelist:
            log.warning("WARNING: not found in the log: %s", file)

    # Final statistics
    # Suggestion: use git-log --before=mtime to brag about skipped log entries
    def log_info(msg, *a, width=13):
        ifmt = '{:%d,}'    % (width,)  # not using 'n' for consistency with ffmt
        ffmt = '{:%d,.2f}' % (width,)
        # %-formatting lacks a thousand separator, must pre-render with .format()
        log.info(msg.replace('%d', ifmt).replace('%f', ffmt).format(*a))

    log_info(
        "Statistics:\n"
        "%f seconds\n"
        "%d log lines processed\n"
        "%d commits evaluated",
        time.time() - start, stats['loglines'], stats['commits'])

    if args.dirs:
        if stats['direrrors']: log_info("%d directory update errors", stats['direrrors'])
        log_info("%d directories updated", stats['dirtouches'])

    if stats['touches'] != stats['totalfiles']:
                        log_info("%d files",              stats['totalfiles'])
    if stats['skip']:   log_info("%d files skipped",      stats['skip'])
    if stats['files']:  log_info("%d files missing",      stats['files'])
    if stats['errors']: log_info("%d file update errors", stats['errors'])

    log_info("%d files updated", stats['touches'])

    if args.test:
        log.info("TEST RUN - No files modified!")


# Keep only essential, global assignments here. Any other logic must be in main()
log = setup_logging()
args = parse_args()

# Set the actual touch() and other functions based on command-line arguments
if args.unique_times:
    touch = touch_ns
    isodate = isodate_ns

# Make sure this is always set last to ensure --test behaves as intended
if args.test:
    touch = dummy

# UI done, it's showtime!
try:
    sys.exit(main())
except KeyboardInterrupt:
    log.info("\nAborting")
    signal.signal(signal.SIGINT, signal.SIG_DFL)
    os.kill(os.getpid(), signal.SIGINT)