[PATCH v3] branch: show rebase/bisect info when possible instead of "(no branch)"

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

This prints more helpful info when HEAD is detached: is it detached
because of bisect or rebase? What is the original branch name in those
cases?

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Keep "no branch" in all cases. Just append "rebasing/bisecting [%s]"
 when applicable.

 builtin/branch.c            | 44 +++++++++++++++++++++++++++++++++++++++++++-
 t/t6030-bisect-porcelain.sh |  2 +-
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index 6371bf9..26c0c3d 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -550,6 +550,48 @@ static int calc_maxwidth(struct ref_list *refs)
 	return w;
 }
 
+static char *get_head_description()
+{
+	struct stat st;
+	struct strbuf sb = STRBUF_INIT;
+	struct strbuf result = STRBUF_INIT;
+	int bisect = 0;
+	int ret;
+	if (!stat(git_path("rebase-merge"), &st) && S_ISDIR(st.st_mode))
+		ret = strbuf_read_file(&sb, git_path("rebase-merge/head-name"), 0);
+	else if (!access(git_path("rebase-apply/rebasing"), F_OK))
+		ret = strbuf_read_file(&sb, git_path("rebase-apply/head-name"), 0);
+	else if (!access(git_path("BISECT_LOG"), F_OK)) {
+		ret = strbuf_read_file(&sb, git_path("BISECT_START"), 0);
+		bisect = 1;
+	} else
+		return xstrdup(_("(no branch)"));
+
+	if (ret <= 0) {
+		if (bisect)
+			return xstrdup(_("(no branch, bisecting)"));
+		else
+			return xstrdup(_("_(no branch, rebasing)"));
+	}
+
+	while (sb.len && sb.buf[sb.len - 1] == '\n')
+		strbuf_setlen(&sb, sb.len - 1);
+
+	if (bisect) {
+		unsigned char sha1[20];
+		if (!get_sha1_hex(sb.buf, sha1))
+			strbuf_addstr(&result, _("(no branch, bisecting)"));
+		else
+			strbuf_addf(&result, _("(no branch, bisecting %s)"), sb.buf);
+	} else {
+		if (!prefixcmp(sb.buf, "refs/heads/"))
+			strbuf_addf(&result, _("(no branch, rebasing %s)"), sb.buf + 11);
+		else
+			strbuf_addstr(&result, _("(no branch, rebasing)"));
+	}
+	strbuf_release(&sb);
+	return strbuf_detach(&result, NULL);
+}
 
 static void show_detached(struct ref_list *ref_list)
 {
@@ -557,7 +599,7 @@ static void show_detached(struct ref_list *ref_list)
 
 	if (head_commit && is_descendant_of(head_commit, ref_list->with_commit)) {
 		struct ref_item item;
-		item.name = xstrdup(_("(no branch)"));
+		item.name = get_head_description();
 		item.width = utf8_strwidth(item.name);
 		item.kind = REF_LOCAL_BRANCH;
 		item.dest = NULL;
diff --git a/t/t6030-bisect-porcelain.sh b/t/t6030-bisect-porcelain.sh
index 3e0e15f..9b6f0d0 100755
--- a/t/t6030-bisect-porcelain.sh
+++ b/t/t6030-bisect-porcelain.sh
@@ -164,7 +164,7 @@ test_expect_success 'bisect start: existing ".git/BISECT_START" not modified if
 	cp .git/BISECT_START saved &&
 	test_must_fail git bisect start $HASH4 foo -- &&
 	git branch > branch.output &&
-	test_i18ngrep "* (no branch)" branch.output > /dev/null &&
+	test_i18ngrep "* (no branch, bisecting other)" branch.output > /dev/null &&
 	test_cmp saved .git/BISECT_START
 '
 test_expect_success 'bisect start: no ".git/BISECT_START" if mistaken rev' '
-- 
1.8.1.2.536.gf441e6d