merge: do not abort early if one strategy fails to handle the merge

builtin/merge is setup to allow multiple strategies to be specified,
and it will find the "best" result and use it.  This is defeated if
some of the merge strategies abort early when they cannot handle the
merge.  Fix the logic that calls recursive and ort to not do such an
early abort, but instead return "2" or "unhandled" so that the next
strategy can try to handle the merge.

Coming up with a testcase for this is somewhat difficult, since
recursive and ort both handle nearly any two-headed merge (there is
a separate code path that checks for non-two-headed merges and
already returns "2" for them).  So use a somewhat synthetic testcase
of having the index not match HEAD before the merge starts, since all
merge strategies will abort for that.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 18 insertions, 1 deletions

diff --git a/t/t6402-merge-rename.sh b/t/t6402-merge-rename.sh
index 3a32b1a..772238e 100755
--- a/t/t6402-merge-rename.sh
+++ b/t/t6402-merge-rename.sh
@@ -210,7 +210,7 @@ test_expect_success 'updated working tree file should prevent the merge' '
 	echo >>M one line addition &&
 	cat M >M.saved &&
 	git update-index M &&
-	test_expect_code 128 git pull --no-rebase . yellow &&
+	test_expect_code 2 git pull --no-rebase . yellow &&
 	test_cmp M M.saved &&
 	rm -f M.saved
 '
diff --git a/t/t6424-merge-unrelated-index-changes.sh b/t/t6424-merge-unrelated-index-changes.sh
index 187c761..615061c 100755
--- a/t/t6424-merge-unrelated-index-changes.sh
+++ b/t/t6424-merge-unrelated-index-changes.sh
@@ -275,4 +275,20 @@ test_expect_success 'subtree' '
 	test_path_is_missing .git/MERGE_HEAD
 '
 
+test_expect_success 'with multiple strategies, recursive or ort failure do not early abort' '
+	git reset --hard &&
+	git checkout B^0 &&
+
+	test_seq 0 10 >a &&
+	git add a &&
+
+	sane_unset GIT_TEST_MERGE_ALGORITHM &&
+	test_must_fail git merge -s recursive -s ort -s octopus C^0 >output 2>&1 &&
+
+	grep "Trying merge strategy recursive..." output &&
+	grep "Trying merge strategy ort..." output &&
+	grep "Trying merge strategy octopus..." output &&
+	grep "No merge strategy handled the merge." output
+'
+
 test_done
diff --git a/t/t6439-merge-co-error-msgs.sh b/t/t6439-merge-co-error-msgs.sh
index 5bfb027..52cf0c8 100755
--- a/t/t6439-merge-co-error-msgs.sh
+++ b/t/t6439-merge-co-error-msgs.sh
@@ -47,6 +47,7 @@ test_expect_success 'untracked files overwritten by merge (fast and non-fast for
 		export GIT_MERGE_VERBOSITY &&
 		test_must_fail git merge branch 2>out2
 	) &&
+	echo "Merge with strategy ${GIT_TEST_MERGE_ALGORITHM:-ort} failed." >>expect &&
 	test_cmp out2 expect &&
 	git reset --hard HEAD^
 '