[PATCH 4/4] merge: apply autostash if merge strategy fails

["Philippe Blain via GitGitGadget" <gitgitgadget@gmail.com>]

From: Philippe Blain <levraiphilippeblain@gmail.com>

Since 'git merge' learned '--autostash' in a03b55530a (merge: teach
--autostash option, 2020-04-07), 'cmd_merge', once it is determined that
we have to create a merge commit, calls 'create_autostash' if
'--autostash' is given.

As explained in a03b55530a, and made more abvious by the tests added in
that commit, the autostash is then applied if the merge succeeds, either
directly or by committing (after conflict resolution or if '--no-commit'
was given), or if the merge is aborted with 'git merge --abort'. In some
other cases, like the user calling 'git reset --merge' or 'git merge
--quit', the autostash is not applied, but saved in the stash list.

However, there exists a scenario that creates an autostash but does not
apply nor save it to the stash list: if the chosen merge strategy
completely fails to handle the merge, i.e. 'try_merge_strategy' returns
2.

Apply the autostash in that case also. An easy way to test that is to
try to merge more than two commits but explicitely ask for the 'recursive'
merge strategy.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
---
 builtin/merge.c  | 1 +
 t/t7600-merge.sh | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/builtin/merge.c b/builtin/merge.c
index 788a6b0cd55..d44c14a21a3 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1709,6 +1709,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		else
 			fprintf(stderr, _("Merge with strategy %s failed.\n"),
 				use_strategies[0]->name);
+		apply_autostash(git_path_merge_autostash(the_repository));
 		ret = 2;
 		goto done;
 	} else if (best_strategy == wt_strategy)
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index 216113d3537..2ef39d3088e 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -732,6 +732,14 @@ test_expect_success 'octopus merge with --autostash' '
 	test_cmp result.1-3-5-9 file
 '
 
+test_expect_success 'failed merge (exit 2) with --autostash' '
+	git reset --hard c1 &&
+	git merge-file file file.orig file.5 &&
+	test_must_fail git merge -s recursive --autostash c2 c3 2>err &&
+	test_i18ngrep "Applied autostash." err &&
+	test_cmp result.1-5 file
+'
+
 test_expect_success 'conflicted merge with --autostash, --abort restores stash' '
 	git reset --hard c3 &&
 	cp file.1 file &&
-- 
gitgitgadget