From edc1cd049cfa01e7d6249ea199725d2448858704 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 17 Jun 2018 13:04:39 +0100
Subject: [PATCH] git-debrebase: Use git-deborig style upstream commitish
 finding

As discussed in email with Sean.

We could use git-deborig --just-print --version= but its error
handling is rather troublesome.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 git-debrebase                  | 18 +++++++++++++++++-
 git-debrebase.1.pod            |  5 ++++-
 tests/tests/gdr-newupstream-v0 |  7 ++++++-
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/git-debrebase b/git-debrebase
index 769b9b94..3de0aa9f 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -1140,7 +1140,23 @@ sub cmd_new_upstream_v0 () {
     my $new_version = (new Dpkg::Version scalar(shift @ARGV), check => 1);
     my $new_upstream_version = $new_version->version();
 
-    my $new_upstream = git_rev_parse (shift @ARGV // 'upstream');
+    my $new_upstream = shift @ARGV;
+    if (!defined $new_upstream) {
+	my @tried;
+	# todo: at some point maybe use git-deborig to do this
+	foreach my $tagpfx ('', 'v', 'upstream/') {
+	    my $tag = $tagpfx.(dep14_version_mangle $new_upstream_version);
+	    $new_upstream = git_get_ref "refs/tags/$tag";
+	    last if length $new_upstream;
+	    push @tried, $tag;
+	}
+	if (!length $new_upstream) {
+	    fail "Could not determine appropriate upstream commitish.\n".
+		" (Tried these tags: @tried)\n".
+		" Check version, and specify upstream commitish explicitly.";
+	}
+    }
+    $new_upstream = git_rev_parse $new_upstream;
 
     record_ffq_auto();
 
diff --git a/git-debrebase.1.pod b/git-debrebase.1.pod
index 4d4c85a9..f17f1d67 100644
--- a/git-debrebase.1.pod
+++ b/git-debrebase.1.pod
@@ -142,7 +142,10 @@ The <upstream-details> are, optionally, in order:
 =item <upstream-commit-ish>
 
 The new upstream branch (or commit-ish).
-Default is C<upstream>.
+The default is to look for one of these tags, in this order:
+U vU upstream/U;
+where U is the new upstream version.
+(This is the same algorithm as L<git-deborig(1)>.)
 
 It is a snag if the upstream contains a debian/ directory;
 if forced to proceed,
diff --git a/tests/tests/gdr-newupstream-v0 b/tests/tests/gdr-newupstream-v0
index 9b283c0b..485c8084 100755
--- a/tests/tests/gdr-newupstream-v0
+++ b/tests/tests/gdr-newupstream-v0
@@ -30,6 +30,11 @@ v=2.1-1
 
 git checkout master
 
+t-expect-fail F:'Could not determine appropriate upstream commitish' \
+t-git-debrebase new-upstream-v0 $v
+
+git tag v2.1 upstream
+
 t-git-debrebase new-upstream-v0 $v
 t-gdr-good laundered
 
@@ -49,7 +54,7 @@ anchor=$(perl <../anal.anch -ne '
 	exit;
 ')
 
-t-git-debrebase --anchor=$anchor -fanchor-treated new-upstream-v0 $v
+t-git-debrebase --anchor=$anchor -fanchor-treated new-upstream-v0 $v upstream
 t-gdr-good laundered
 
 t-git-debrebase stitch
-- 
2.30.2