[PATCH] git-svn: understand grafts when doing dcommit

[Eric Wong <normalperson@yhbt.net>]

Use the rev-list --parents functionality to read the parents
of the commit.  cat-file only shows the raw object with the
original parents and doesn't take into account grafts; so
we'll rely on rev-list machinery for the smarts here.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
---
  Junio C Hamano <gitster@pobox.com> wrote:
  > "Joakim Tjernlund" <joakim.tjernlund@transmode.se> writes:
  > 
  > > hmm, I think git-cat-file is to blame.
  > > git-cat-file commit da783cce390ce013b19f1d308ea6813269c6a6b5 does
  > > not list list any parent...
  > 
  > The plumbing cat-file does not deal with grafts and this is
  > deliberate.  Otherwise you would not be able to find the true
  > set of parents when you'd want to.
  > 
  > So do not blame cat-file, but blame the Porcelain that uses
  > cat-file to read a commit object, without annotating what it
  > read with what is in grafts, in this case your command line
  > experiment ;-).
  > 
  > The log family of commands and rev-list plumbing while
  > traversing commit ancestry chain do take grafts into account.
  > 
  > One caveat is pretty=raw output format shows true parents
  > without grafts on "parent " header line, while the "commit "
  > fake header prepended in the output for each commit shows the
  > parents that takes into account.
  > 
  > To illustrate, if you forge the history and say the parent of
  > 1ddea77 is 5da1606 (when the true parent is 820eca68) with
  > grafts mechanism, here is what happens:
  > 
  >     $ echo '1ddea77e449ef28d8a7c74521af21121ab01abc0 5da1606d0bf5b970fadfa0ca91618a1e871f6755' >.git/info/grafts
  >     $ git show -s --pretty=raw --parents 1ddea77
  >     commit 1ddea77e449ef28d8a7c74521af21121ab01abc0 5da1606d0bf5b970fadfa0ca91618a1e871f6755
  >     tree e9e61bc801438062978ff47b0963c536ed1e51a9
  >     parent 820eca68c2577d7499d203d7f4f7ae479b577683
  >     author Nick Hengeveld <nickh@reactrix.com> 1127757131 -0700
  >     committer Junio C Hamano <junkio@cox.net> 1127805558 -0700
  > 
  >         [PATCH] Return CURL error message when object transfer fails
  > 
  >         Return CURL error message when object transfer fails
  >         ...

  Interesting.  I didn't know about the --parents option before.

 git-svn.perl |   11 +++--------
 1 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/git-svn.perl b/git-svn.perl
index fbd4691..f818160 100755
--- a/git-svn.perl
+++ b/git-svn.perl
@@ -841,14 +841,9 @@ sub working_head_info {
 
 sub read_commit_parents {
 	my ($parents, $c) = @_;
-	my ($fh, $ctx) = command_output_pipe(qw/cat-file commit/, $c);
-	while (<$fh>) {
-		chomp;
-		last if '';
-		/^parent ($sha1)/ or next;
-		push @{$parents->{$c}}, $1;
-	}
-	close $fh; # break the pipe
+	chomp(my $p = command_oneline(qw/rev-list --parents -1/, $c));
+	$p =~ s/^($c)\s*// or die "rev-list --parents -1 $c failed!\n";
+	@{$parents->{$c}} = split(/ /, $p);
 }
 
 sub linearize_history {
-- 
Eric Wong