dgit: Fix suggested diff rune in split brain mode

In split brain mode, with unexpected diffs, print dgit view commitid
in suggested diff rune.

HEAD is wrong in this case.

Closes:#886443.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/dgit b/dgit
index 3a9b46c..aa8f771 100755
--- a/dgit
+++ b/dgit
@@ -4238,13 +4238,14 @@ END
     my $r = system @diffcmd;
     if ($r) {
 	if ($r==256) {
+	    my $referent = $split_brain ? $dgithead : 'HEAD';
 	    my $diffs = cmdoutput @git, qw(diff --stat), $tree, $dgithead;
 	    fail <<END
 HEAD specifies a different tree to $dscfn:
 $diffs
 Perhaps you forgot to build.  Or perhaps there is a problem with your
  source tree (see dgit(7) for some hints).  To see a full diff, run
-   git diff $tree HEAD
+   git diff $tree $referent
 END
 	} else {
 	    failedcmd @diffcmd;