dgit: Interoperate with git-debrebase, automatically

* Recognise gdr branches, by the presence of corresponding
  ffq-prev or debrebase-last refs.

* Before trying to do our own multi-patch linear quilt fixup, on a gdr
  branch, see if gdr can do it.  If so that is faster and better.

* If our branch is an unstitched gdr branch, which would be ff from
  the archive if we were to stitch it, then do so.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/dgit b/dgit
index c8567ed473d838cab555bfd5c118a7d695eb4bef..ebf44de800ed399aa56644928f01461c9694d67a 100755 (executable)
--- a/dgit
+++ b/dgit
@@ -292,6 +292,32 @@ sub dgit_privdir () {
     our $dgit_privdir_made //= ensure_a_playground 'dgit';
 }
 
+sub branch_gdr_info ($$) {
+    my ($symref, $head) = @_;
+    my ($status, $msg, $current, $ffq_prev, $gdrlast) =
+       gdr_ffq_prev_branchinfo($symref);
+    return () unless $status eq 'branch';
+    $ffq_prev = git_get_ref $ffq_prev;
+    $gdrlast  = git_get_ref $gdrlast;
+    $gdrlast &&= is_fast_fwd $gdrlast, $head;
+    return ($ffq_prev, $gdrlast);
+}
+
+sub branch_is_gdr ($$) {
+    my ($symref, $head) = @_;
+    my ($ffq_prev, $gdrlast) = branch_gdr_info($symref, $head);
+    return 0 unless $ffq_prev || $gdrlast;
+    return 1;
+}
+
+sub branch_is_gdr_unstitched_ff ($$$) {
+    my ($symref, $head, $ancestor) = @_;
+    my ($ffq_prev, $gdrlast) = branch_gdr_info($symref, $head);
+    return 0 unless $ffq_prev;
+    return 0 unless is_fast_fwd $ancestor, $ffq_prev;
+    return 1;
+}
+
 #---------- remote protocol support, common ----------
 
 # remote push initiator/responder protocol:
@@ -4220,7 +4246,14 @@ END
     my $format = getfield $dsc, 'Format';
     printdebug "format $format\n";
 
+    my $symref = git_get_symref();
     my $actualhead = git_rev_parse('HEAD');
+
+    if (branch_is_gdr_unstitched_ff($symref, $actualhead, $archive_hash)) {
+       runcmd_ordryrun_local @git_debrebase, 'stitch';
+       $actualhead = git_rev_parse('HEAD');
+    }
+
     my $dgithead = $actualhead;
     my $maintviewhead = undef;
 
@@ -5425,6 +5458,32 @@ END
 
     my $clogp = parsechangelog();
     my $headref = git_rev_parse('HEAD');
+    my $symref = git_get_symref();
+
+    if ($quilt_mode eq 'linear'
+       && !$fopts->{'single-debian-patch'}
+       && branch_is_gdr($symref, $headref)) {
+       # This is much faster.  It also makes patches that gdr
+       # likes better for future updates without laundering.
+       #
+       # However, it can fail in some casses where we would
+       # succeed: if there are existing patches, which correspond
+       # to a prefix of the branch, but are not in gbp/gdr
+       # format, gdr will fail (exiting status 7), but we might
+       # be able to figure out where to start linearising.  That
+       # will be slower so hopefully there's not much to do.
+       my @cmd = (@git_debrebase,
+                  qw(--noop-ok -funclean-mixed -funclean-ordering
+                     make-patches --quiet-would-amend));
+       # We tolerate soe snags that gdr wouldn't, by default.
+       if (act_local()) {
+           $!=0; $?=-1;
+           failedcmd @cmd if system @cmd and $?!=7;
+       } else {
+           dryrun_report @cmd;
+       }
+       $headref = git_rev_parse('HEAD');
+    }
 
     prep_ud();
     changedir $playground;