From f153b639773992dca58aa70128d7ef33a70cf639 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Wed, 8 Feb 2017 23:59:44 +0000
Subject: [PATCH] git-debrebase: avoid rewrite

---
 git-debrebase | 38 +++++++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/git-debrebase b/git-debrebase
index f740ed05..e231b512 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -328,11 +328,13 @@ sub launder ($$$) {
  
     my $committer_authline = calculate_committer_authline();
 
+    my $need_rewrite = 0;
+
     in_workarea sub {
 	mkdir $rd or $!==EEXIST or die $!;
-
 	my $current_method;
-	foreach my $cl (qw(Debian), @deb_cl, qw(Upstream), @ups_cl) {
+	foreach my $cl (qw(Debian), (reverse @deb_cl),
+			qw(Upstream), (reverse @ups_cl)) {
 	    if (!ref $cl) {
 		$current_method = $cl;
 		next;
@@ -347,21 +349,39 @@ sub launder ($$$) {
 	    } elsif ($method eq 'DgitImportDebianUpdate') {
 		$read_tree_debian->($cltree);
 		$rm_tree_cached(qw(debian/patches));
+		$need_rewrite = 1;
 	    } elsif ($method eq 'DgitImportUpstreamUpdate') {
 		$read_tree_upstream->($cltree);
 		push @parents, map { $_->{CommitId} } @{ $cl->{OrigParents} };
+		$need_rewrite = 1;
 	    } else {
 		confess "$method ?";
 	    }
 	    my $newtree = cmdoutput @git, qw(write-tree);
-	    my $ch = $cl->{Msg};
+	    my $ch = $cl->{Hdr};
 	    $ch =~ s{^tree .*}{tree $newtree}m or confess "$ch ?";
-	    $ch =~ s{^committer .*$}{$committer_authline}m or confess "$ch ?";
-	    open CD, ">", "$rd/m" or die $!;
-	    print CD $ch, "\n", $cl->{Msg}; or die $!;
-	    close CD or die $!;
-	    my $newcommit = cmdoutput @git, qw(hash-object -t commit), "$rd/m";
-	    $build = $newcommit;
+	    $ch =~ s{^parent .*\n}{}m;
+	    $ch =~ s{(?=^author}{
+		map { "parent $_\n" } @parents
+	    }me or confess "$ch ?";
+	    foreach my $rewrite ($need_rewrite ? 1 : qw(0 1)) {
+		if ($rewrite) {
+		    $ch =~ s{^committer .*$}{$committer_authline}m
+			or confess "$ch ?";
+		    $need_rewrite = 1;
+		}
+		my $cf = "$rd/m$rewrite"
+		open CD, ">", $cf or die $!;
+		print CD $ch, "\n", $cl->{Msg}; or die $!;
+		close CD or die $!;
+		my @cmd = (@git, qw(hash-object));
+		push @cmd, qw(-w) if $rewrite;
+		push @cmd, qw(-t commit), $cf;
+		my $newcommit = cmdoutput @cmd;
+		next unless $rewrite or $newcommit eq $cl->{CommitId};
+		$build = $newcommit;
+		last;
+	    }
 	}
     };
 
-- 
2.30.2