contrib/git-svn: allow rebuild to work on non-linear remote heads

Because committing back to an SVN repository from different
machines can result in different lineages, two different
repositories running git-svn can result in different commit
SHA1s (but of the same tree).  Sometimes trees that are tracked
independently are merged together (usually via children),
resulting in non-unique git-svn-id: lines in rev-list.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/contrib/git-svn/git-svn.perl b/contrib/git-svn/git-svn.perl
index cf233ef..f3fc3ec 100755 (executable)
--- a/contrib/git-svn/git-svn.perl
+++ b/contrib/git-svn/git-svn.perl
@@ -850,11 +850,23 @@ sub assert_revision_unknown {
        }
 }
 
+sub trees_eq {
+       my ($x, $y) = @_;
+       my @x = safe_qx('git-cat-file','commit',$x);
+       my @y = safe_qx('git-cat-file','commit',$y);
+       if (($y[0] ne $x[0]) || $x[0] !~ /^tree $sha1\n$/
+                               || $y[0] !~ /^tree $sha1\n$/) {
+               print STDERR "Trees not equal: $y[0] != $x[0]\n";
+               return 0
+       }
+       return 1;
+}
+
 sub assert_revision_eq_or_unknown {
        my ($revno, $commit) = @_;
        if (-f "$REV_DIR/$revno") {
                my $current = file_to_s("$REV_DIR/$revno");
-               if ($commit ne $current) {
+               if (($commit ne $current) && !trees_eq($commit, $current)) {
                        croak "$REV_DIR/$revno already exists!\n",
                                "current: $current\nexpected: $commit\n";
                }