rebase: introduce and use pseudo-ref REBASE_HEAD

The new command `git rebase --show-current-patch` is useful for seeing
the commit related to the current rebase state. Some however may find
the "git show" command behind it too limiting. You may want to
increase context lines, do a diff that ignores whitespaces...

For these advanced use cases, the user can execute any command they
want with the new pseudo ref REBASE_HEAD.

This also helps show where the stopped commit is from, which is hard
to see from the previous patch which implements --show-current-patch.

Helped-by: Tim Landscheidt <tim@tim-landscheidt.de>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

9 files changed, 25 insertions, 6 deletions

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 7ef9577..0b29e48 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -252,7 +252,8 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 
 --show-current-patch::
 	Show the current patch in an interactive rebase or when rebase
-	is stopped because of conflicts.
+	is stopped because of conflicts. This is the equivalent of
+	`git show REBASE_HEAD`.
 
 -m::
 --merge::
diff --git a/builtin/am.c b/builtin/am.c
index 37219fc..21aedec 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1011,6 +1011,7 @@ static void am_setup(struct am_state *state, enum patch_format patch_format,
 
 	if (mkdir(state->dir, 0777) < 0 && errno != EEXIST)
 		die_errno(_("failed to create directory '%s'"), state->dir);
+	delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
 
 	if (split_mail(state, patch_format, paths, keep_cr) < 0) {
 		am_destroy(state);
@@ -1110,6 +1111,7 @@ static void am_next(struct am_state *state)
 
 	oidclr(&state->orig_commit);
 	unlink(am_path(state, "original-commit"));
+	delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
 
 	if (!get_oid("HEAD", &head))
 		write_state_text(state, "abort-safety", oid_to_hex(&head));
@@ -1441,6 +1443,8 @@ static int parse_mail_rebase(struct am_state *state, const char *mail)
 
 	oidcpy(&state->orig_commit, &commit_oid);
 	write_state_text(state, "original-commit", oid_to_hex(&commit_oid));
+	update_ref("am", "REBASE_HEAD", &commit_oid,
+		   NULL, REF_NO_DEREF, UPDATE_REFS_DIE_ON_ERR);
 
 	return 0;
 }
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 2bd30d6..8777805 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -439,7 +439,7 @@ __git_refs ()
 			track=""
 			;;
 		*)
-			for i in HEAD FETCH_HEAD ORIG_HEAD MERGE_HEAD; do
+			for i in HEAD FETCH_HEAD ORIG_HEAD MERGE_HEAD REBASE_HEAD; do
 				case "$i" in
 				$match*)
 					if [ -e "$dir/$i" ]; then
diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index 0c0f8ab..a613156 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -199,12 +199,14 @@ make_patch () {
 
 die_with_patch () {
 	echo "$1" > "$state_dir"/stopped-sha
+	git update-ref REBASE_HEAD "$1"
 	make_patch "$1"
 	die "$2"
 }
 
 exit_with_patch () {
 	echo "$1" > "$state_dir"/stopped-sha
+	git update-ref REBASE_HEAD "$1"
 	make_patch $1
 	git rev-parse --verify HEAD > "$amend"
 	gpg_sign_opt_quoted=${gpg_sign_opt:+$(git rev-parse --sq-quote "$gpg_sign_opt")}
@@ -841,7 +843,7 @@ To continue rebase after editing, run:
 	exit
 	;;
 show-current-patch)
-	exec git show "$(cat "$state_dir/stopped-sha")" --
+	exec git show REBASE_HEAD --
 	;;
 esac
 
@@ -858,6 +860,7 @@ fi
 
 orig_head=$(git rev-parse --verify HEAD) || die "$(gettext "No HEAD?")"
 mkdir -p "$state_dir" || die "$(eval_gettext "Could not create temporary \$state_dir")"
+rm -f "$(git rev-parse --git-path REBASE_HEAD)"
 
 : > "$state_dir"/interactive || die "$(gettext "Could not mark as interactive")"
 write_basic_state
diff --git a/git-rebase--merge.sh b/git-rebase--merge.sh
index 0a96dfa..957688f 100644
--- a/git-rebase--merge.sh
+++ b/git-rebase--merge.sh
@@ -57,6 +57,7 @@ call_merge () {
 	echo "$msgnum" >"$state_dir/msgnum"
 	cmt="$(cat "$state_dir/cmt.$msgnum")"
 	echo "$cmt" > "$state_dir/current"
+	git update-ref REBASE_HEAD "$cmt"
 	hd=$(git rev-parse --verify HEAD)
 	cmt_name=$(git symbolic-ref HEAD 2> /dev/null || echo HEAD)
 	eval GITHEAD_$cmt='"${cmt_name##refs/heads/}~$(($end - $msgnum))"'
@@ -138,13 +139,14 @@ skip)
 	return
 	;;
 show-current-patch)
-	exec git show "$(cat "$state_dir/current")" --
+	exec git show REBASE_HEAD --
 	;;
 esac
 
 mkdir -p "$state_dir"
 echo "$onto_name" > "$state_dir/onto_name"
 write_basic_state
+rm -f "$(git rev-parse --git-path REBASE_HEAD)"
 
 msgnum=0
 for cmt in $(git rev-list --reverse --no-merges "$revisions")
diff --git a/git-rebase.sh b/git-rebase.sh
index 41c915d..a13a581 100755
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -182,6 +182,7 @@ You can run "git stash pop" or "git stash drop" at any time.
 }
 
 finish_rebase () {
+	rm -f "$(git rev-parse --git-path REBASE_HEAD)"
 	apply_autostash &&
 	{ git gc --auto || true; } &&
 	rm -rf "$state_dir"
diff --git a/sequencer.c b/sequencer.c
index 4d3f605..f692221 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1792,6 +1792,9 @@ static int make_patch(struct commit *commit, struct replay_opts *opts)
 	p = short_commit_name(commit);
 	if (write_message(p, strlen(p), rebase_path_stopped_sha(), 1) < 0)
 		return -1;
+	if (update_ref("rebase", "REBASE_HEAD", &commit->object.oid,
+		       NULL, REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR))
+		res |= error(_("could not update %s"), "REBASE_HEAD");
 
 	strbuf_addf(&buf, "%s/patch", get_dir(opts));
 	memset(&log_tree_opt, 0, sizeof(log_tree_opt));
@@ -2043,6 +2046,7 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 			unlink(rebase_path_author_script());
 			unlink(rebase_path_stopped_sha());
 			unlink(rebase_path_amend());
+			delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
 		}
 		if (item->command <= TODO_SQUASH) {
 			if (is_rebase_i(opts))
diff --git a/t/t3400-rebase.sh b/t/t3400-rebase.sh
index 09943d6..72d9564 100755
--- a/t/t3400-rebase.sh
+++ b/t/t3400-rebase.sh
@@ -306,7 +306,8 @@ test_expect_success 'rebase--merge.sh and --show-current-patch' '
 		test_must_fail git rebase --merge --onto init HEAD^ &&
 		git rebase --show-current-patch >actual.patch &&
 		GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
-		grep "show.*$(git rev-parse two)" stderr
+		grep "show.*REBASE_HEAD" stderr &&
+		test "$(git rev-parse REBASE_HEAD)" = "$(git rev-parse two)"
 	)
 '
 
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 3af6f14..23a54a4 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -227,7 +227,10 @@ test_expect_success 'stop on conflicting pick' '
 
 test_expect_success 'show conflicted patch' '
 	GIT_TRACE=1 git rebase --show-current-patch >/dev/null 2>stderr &&
-	grep "show.*$(cat "$state_dir/stopped-sha")" stderr
+	grep "show.*REBASE_HEAD" stderr &&
+	# the original stopped-sha1 is abbreviated
+	stopped_sha1="$(git rev-parse $(cat ".git/rebase-merge/stopped-sha"))" &&
+	test "$(git rev-parse REBASE_HEAD)" = "$stopped_sha1"
 '
 
 test_expect_success 'abort' '