git-svn: Added 'find-rev' command

This patch adds a new 'find-rev' command to git-svn that lets you easily
translate between SVN revision numbers and git tree-ish.

Signed-off-by: Adam Roben <aroben@apple.com>
Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-svn.txt

@@ -159,6 +159,11 @@ New features:
 Any other arguments are passed directly to `git log'
 
 --
+'find-rev'::
+	When given an SVN revision number of the form 'rN', returns the
+	corresponding git commit hash.  When given a tree-ish, returns the
+	corresponding SVN revision number.
+
 'set-tree'::
 	You should consider using 'dcommit' instead of this command.
 	Commit specified commit or tree objects to SVN.  This relies on

git-svn.perl

@@ -141,6 +141,8 @@ my %cmd = (
 			  'color' => \$Git::SVN::Log::color,
 			  'pager=s' => \$Git::SVN::Log::pager,
 			} ],
+	'find-rev' => [ \&cmd_find_rev, "Translate between SVN revision numbers and tree-ish",
+			{ } ],
 	'rebase' => [ \&cmd_rebase, "Fetch and rebase your working directory",
 			{ 'merge|m|M' => \$_merge,
 			  'verbose|v' => \$_verbose,
@@ -428,6 +430,28 @@ sub cmd_dcommit {
 	command_noisy(@finish, $gs->refname);
 }
 
+sub cmd_find_rev {
+	my $revision_or_hash = shift;
+	my $result;
+	if ($revision_or_hash =~ /^r\d+$/) {
+		my $desired_revision = substr($revision_or_hash, 1);
+		my ($fh, $ctx) = command_output_pipe('rev-list', 'HEAD');
+		while (my $hash = <$fh>) {
+			chomp($hash);
+			my (undef, $rev, undef) = cmt_metadata($hash);
+			if ($rev && $rev eq $desired_revision) {
+				$result = $hash;
+				last;
+			}
+		}
+		command_close_pipe($fh, $ctx);
+	} else {
+		my (undef, $rev, undef) = cmt_metadata($revision_or_hash);
+		$result = $rev;
+	}
+	print "$result\n" if $result;
+}
+
 sub cmd_rebase {
 	command_noisy(qw/update-index --refresh/);
 	my ($url, $rev, $uuid, $gs) = working_head_info('HEAD');