[PATCH v3 4/4] merge: save merge state earlier

[Michael J Gruber <git@grubix.eu>]

If the `git merge` process is killed while waiting for the editor to
finish, the merge state is lost but the prepared merge msg and tree is kept.
So, a subsequent `git commit` creates a squashed merge even when the
user asked for proper merge commit originally.

Demonstrate the problem with a test crafted after the in t7502. The test
requires EXECKEEPSPID (thus does not run under MINGW).

Save the merge state earlier (in the non-squash case) so that it does
not get lost. This makes the test pass.

Reported-by: hIpPy <hippy2981@gmail.com>
Signed-off-by: Michael J Gruber <git@grubix.eu>
---
 builtin/merge.c  |  2 ++
 t/t7600-merge.sh | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/builtin/merge.c b/builtin/merge.c
index db3335b3bf..2d5c45a904 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -758,6 +758,7 @@ N_("Please enter a commit message to explain why this merge is necessary,\n"
    "Lines starting with '%c' will be ignored, and an empty message aborts\n"
    "the commit.\n");
 
+static void write_merge_heads(struct commit_list *);
 static void prepare_to_commit(struct commit_list *remoteheads)
 {
 	struct strbuf msg = STRBUF_INIT;
@@ -769,6 +770,7 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 		strbuf_commented_addf(&msg, _(merge_editor_comment), comment_line_char);
 	if (signoff)
 		append_signoff(&msg, ignore_non_trailer(msg.buf, msg.len), 0);
+	write_merge_heads(remoteheads);
 	write_file_buf(git_path_merge_msg(), msg.buf, msg.len);
 	if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
 			    git_path_merge_msg(), "merge", NULL))
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index 2ebda509ac..80194b79f9 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -774,4 +774,19 @@ test_expect_success 'merge can be completed with --continue' '
 	verify_parents $c0 $c1
 '
 
+write_script .git/FAKE_EDITOR <<EOF
+# kill -TERM command added below.
+EOF
+
+test_expect_success EXECKEEPSPID 'killed merge can be completed with --continue' '
+	git reset --hard c0 &&
+	! "$SHELL_PATH" -c '\''
+	  echo kill -TERM $$ >> .git/FAKE_EDITOR
+	  GIT_EDITOR=.git/FAKE_EDITOR
+	  export GIT_EDITOR
+	  exec git merge --no-ff --edit c1'\'' &&
+	git merge --continue &&
+	verify_parents $c0 $c1
+'
+
 test_done
-- 
2.14.1.426.g4352aa77a5