merge: allow fast-forward when merging a tracked tagjc/allow-ff-merging-kept-tags

Long time ago at fab47d05 ("merge: force edit and no-ff mode when
merging a tag object", 2011-11-07), "git merge" was made to always
create a merge commit when merging a tag, even when the side branch
being merged is a descendant of the current branch.

This default is good for merges made by upstream maintainers to
integrate work signed by downstream contributors, but will leave
pointless no-ff merges when downstream contributors pull a newer
release tag to make their long-running topic branches catch up with
the upstream.  When there is no local work left on the topic, such a
merge should simply fast-forward to the commit pointed at by the
release tag.

Update the default (again) for "git merge" that merges a tag object
to (1) --no-ff (i.e. create a merge commit even when side branch
fast forwards) if the tag being merged is not at its expected place
in refs/tags/ hierarchy and (2) --ff (i.e. allow fast-forward update
when able) otherwise.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 37 insertions, 1 deletions

diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index dfde6a675a..6736d8d131 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -700,6 +700,42 @@ test_expect_success 'merge --no-ff --edit' '
 	test_cmp expected actual
 '
 
+test_expect_success 'merge annotated/signed tag w/o tracking' '
+	test_when_finished "rm -rf dst; git tag -d anno1" &&
+	git tag -a -m "anno c1" anno1 c1 &&
+	git init dst &&
+	git rev-parse c1 >dst/expect &&
+	(
+		# c0 fast-forwards to c1 but because this repository
+		# is not a "downstream" whose refs/tags follows along
+		# tag from the "upstream", this pull defaults to --no-ff
+		cd dst &&
+		git pull .. c0 &&
+		git pull .. anno1 &&
+		git rev-parse HEAD^2 >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'merge annotated/signed tag w/ tracking' '
+	test_when_finished "rm -rf dst; git tag -d anno1" &&
+	git tag -a -m "anno c1" anno1 c1 &&
+	git init dst &&
+	git rev-parse c1 >dst/expect &&
+	(
+		# c0 fast-forwards to c1 and because this repository
+		# is a "downstream" whose refs/tags follows along
+		# tag from the "upstream", this pull defaults to --ff
+		cd dst &&
+		git remote add origin .. &&
+		git pull origin c0 &&
+		git fetch origin &&
+		git merge anno1 &&
+		git rev-parse HEAD >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success GPG 'merge --ff-only tag' '
 	git reset --hard c0 &&
 	git commit --allow-empty -m "A newer commit" &&
@@ -718,7 +754,7 @@ test_expect_success GPG 'merge --no-edit tag should skip editor' '
 	git tag -f -s -m "A newer commit" signed &&
 	git reset --hard c0 &&
 
-	EDITOR=false git merge --no-edit signed &&
+	EDITOR=false git merge --no-edit --no-ff signed &&
 	git rev-parse signed^0 >expect &&
 	git rev-parse HEAD^2 >actual &&
 	test_cmp expect actual