[PATCH/RFC] git-svn: Add --convert-timezone option

[Pete Harlan <pgit@pcharlan.com>]

By default git svn stores timestamps of fetched commits in
Subversion's UTC format, to facilitate interoperating with a
Subversion repository.

If you're using git svn to convert a repository to Git and aren't
interested in pushing Git commits back to Subversion, you can use this
option to store timestamps of fetched commits as though they were made
in the local timezone of the host on which git svn is run.  This makes
the times and timezones of a resulting "git log" agree with what "svn
log" shows for the same repository.

Signed-off-by: Pete Harlan <pgit@pcharlan.com>
---

This is a patch I've had floating around for a while.  I haven't
submitted it before because I find the solution ungainly.  There has
to be a better way to convert from one timezone to the other, but I
didn't run across it and now that I've converted away from Subversion
I'm sort of done thinking about it.  I'm submitting it now because
even in its current state it would have saved me some headache.

Also, I'm not sure I'm correct when asserting that converting
timezones like this will break Subversion interoperability.  Eric, if
that isn't true then I can remove that claim and resubmit.  If
converting timezones breaks nothing, then maybe it could even be the
default.

One improvement that I didn't bother to make would be to convert to
different local timezones based on author.  This change uses the
timezone of the machine running git-svn, which in my case was fine.
Using per-author timezones would be nice, but since parse_svn_date()
doesn't already know which author the date is associated with it would
be a more intrusive change.

My primary motivation in this was to reduce transition shock among our
development team.  The fewer ways "git log" looks unhelpfully
different than the old "svn log" the better; converting all commit
times into GMT wasn't going to look friendly.

Comments welcome.

--Pete

 Documentation/git-svn.txt              |    8 ++++
 contrib/completion/git-completion.bash |    2 +-
 git-svn.perl                           |   56 ++++++++++++++++++++++++++++++-
 3 files changed, 63 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-svn.txt b/Documentation/git-svn.txt
index 8d0c421..8811bf0 100644
--- a/Documentation/git-svn.txt
+++ b/Documentation/git-svn.txt
@@ -92,6 +92,14 @@ COMMANDS
 	.git/config file may be specified as an optional command-line
 	argument.

+--convert-timezones;;
+	Store Git commit times in the local timezone instead of UTC.  This
+	makes 'git-log' (even without --date=local) show the same times
+	that `svn log` would in the local timezone.
+
+This breaks interoperability with SVN, but may be cosmetically
+desirable when converting a repository from SVN to Git.
+
 'clone'::
 	Runs 'init' and 'fetch'.  It will automatically create a
 	directory based on the basename of the URL passed to it;
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 8ec782d..597ef3d 100755
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1560,7 +1560,7 @@ _git_svn ()
 			--follow-parent --authors-file= --repack=
 			--no-metadata --use-svm-props --use-svnsync-props
 			--log-window-size= --no-checkout --quiet
-			--repack-flags --user-log-author $remote_opts
+			--repack-flags --user-log-author --convert-timezones $remote_opts
 			"
 		local init_opts="
 			--template= --shared= --trunk= --tags=
diff --git a/git-svn.perl b/git-svn.perl
index ad01e18..c2f600d 100755
--- a/git-svn.perl
+++ b/git-svn.perl
@@ -66,7 +66,7 @@ my ($_stdin, $_help, $_edit,
 	$_version, $_fetch_all, $_no_rebase,
 	$_merge, $_strategy, $_dry_run, $_local,
 	$_prefix, $_no_checkout, $_url, $_verbose,
-	$_git_format, $_commit_url, $_tag);
+	$_git_format, $_commit_url, $_tag, $_convert_timezones);
 $Git::SVN::_follow_parent = 1;
 my %remote_opts = ( 'username=s' => \$Git::SVN::Prompt::_username,
                     'config-dir=s' => \$Git::SVN::Ra::config_dir,
@@ -84,6 +84,7 @@ my %fc_opts = ( 'follow-parent|follow!' => \$Git::SVN::_follow_parent,
 		   \$Git::SVN::_repack_flags,
 		'use-log-author' => \$Git::SVN::_use_log_author,
 		'add-author-from' => \$Git::SVN::_add_author_from,
+		'convert-timezones' => \$_convert_timezones,
 		%remote_opts );

 my ($_trunk, $_tags, $_branches, $_stdlayout);
@@ -2526,12 +2527,63 @@ sub get_untracked {
 	\@out;
 }

+# parse_svn_date(DATE)
+# --------------------
+# Given a date (in UTC) from Subversion, return a string in the format
+# "<TZ Offset> <local date/time>" that Git will use.
+#
+# By default the parsed date will be in UTC for interoperating with
+# Subversion, but if $_convert_timezones is true we'll convert it to
+# the local timezone instead.
 sub parse_svn_date {
 	my $date = shift || return '+0000 1970-01-01 00:00:00';
 	my ($Y,$m,$d,$H,$M,$S) = ($date =~ /^(\d{4})\-(\d\d)\-(\d\d)T
 	                                    (\d\d)\:(\d\d)\:(\d\d).\d+Z$/x) or
 	                                 croak "Unable to parse date: $date\n";
-	"+0000 $Y-$m-$d $H:$M:$S";
+	my $parsed_date;    # Set next.
+
+	if ($_convert_timezones) {
+		# Translate the Subversion datetime to an epoch time.
+		# We need to switch ourselves to $date's timezone,
+		# UTC, for this.
+		my $oldEnvTZ = $ENV{TZ};
+		$ENV{TZ} = 'UTC';
+
+		my $epochUTC =
+		    POSIX::strftime ('%s', $S, $M, $H, $d, $m - 1, $Y - 1900);
+
+		# Determine our local timezone (including DST) at the
+		# time of $epochUTC.  $Git::SVN::Log::TZ stored the
+		# value of TZ, if any, at the time we were run.
+		if (defined $Git::SVN::Log::TZ) {
+			$ENV{TZ} = $Git::SVN::Log::TZ;
+		} else {
+			delete $ENV{TZ};
+		}
+
+		my $ourTZ =
+		    POSIX::strftime ('%Z', $S, $M, $H, $d, $m - 1, $Y - 1900);
+
+		# This converts $epochUTC into our local timezone.
+		my ($sec, $min, $hour, $mday, $mon, $year,
+		    $wday, $yday, $isdst) = localtime ($epochUTC);
+
+		$parsed_date = sprintf ('%s %04d-%02d-%02d %02d:%02d:%02d',
+					$ourTZ, $year + 1900, $mon + 1,
+					$mday, $hour, $min, $sec);
+
+		# Reset us to the timezone in effect when we entered
+		# this routine.
+		if (defined $oldEnvTZ) {
+			$ENV{TZ} = $oldEnvTZ;
+		} else {
+			delete $ENV{TZ};
+		}
+	} else {
+		$parsed_date = "+0000 $Y-$m-$d $H:$M:$S";
+	}
+
+	return $parsed_date;
 }

 sub check_author {
-- 
1.6.1.77.g56257