git-debrebase: merge: Introduce new merge_failed sub

And call it from $nomerge in walk.  Now we produce a sane error
message.

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

1 files changed, 12 insertions, 1 deletions

diff --git a/git-debrebase b/git-debrebase
index a6a02b1..abf9157 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -368,6 +368,16 @@ sub gbp_pq_export ($$$) {
 #  our own patch identification algorithm?
 #  this is an alternative strategy
 
+sub merge_failed ($$) {
+    my ($wrecknotes, $emsg) = @_;
+    my @m;
+    push @m, "Merge resolution failed: $emsg";
+
+    push @m, "See git-debrebase(1) section FAILED MERGES for suggestions.";
+    # ^ xxx this section does not yet exist
+    fail join '', map { "$_\n" } @m;
+}
+
 sub mwrecknote ($$$) {
     my ($wrecknotes, $reftail, $commitish) = @_;
     confess unless defined $commitish;
@@ -1046,7 +1056,8 @@ sub walk ($;$$$) {
     };
 
     my $nomerge = sub {
-	fail "something useful about failed merge attempt @_ xxx".Dumper($cl);
+	my ($emsg) = @_;
+	merge_failed $cl->{MergeWreckNotes}, $emsg;
     };
 
     my $mwrecknote = sub { &mwrecknote($cl->{MergeWreckNotes}, @_); };