[PATCH v2 22/23] worktree: add: auto-vivify new branch when <branch> is omitted

[Eric Sunshine <sunshine@sunshineco.com>]

As a convenience, when <branch> is omitted from "git worktree <path>
<branch>" and neither -b nor -B used, automatically create a new branch
named after <path>, as if "-b $(basename <path>)" was specified. Thus,
"git worktree add ../hotfix" creates a new branch named "hotfix" and
associates it with new worktree "../hotfix".

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---
 Documentation/git-worktree.txt | 8 ++++++--
 builtin/worktree.c             | 8 ++++++--
 t/t2025-worktree-add.sh        | 7 +++++++
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-worktree.txt b/Documentation/git-worktree.txt
index 5ca11f6..938bdab 100644
--- a/Documentation/git-worktree.txt
+++ b/Documentation/git-worktree.txt
@@ -9,7 +9,7 @@ git-worktree - Manage multiple worktrees
 SYNOPSIS
 --------
 [verse]
-'git worktree add' [-f] [--detach] [-b <new-branch>] <path> <branch>
+'git worktree add' [-f] [--detach] [-b <new-branch>] <path> [<branch>]
 'git worktree prune' [-n] [-v] [--expire <expire>]
 
 DESCRIPTION
@@ -45,12 +45,16 @@ pruning should be suppressed. See section "DETAILS" for more information.
 
 COMMANDS
 --------
-add <path> <branch>::
+add <path> [<branch>]::
 
 Check out `<branch>` into a separate working directory, `<path>`, creating
 `<path>` if necessary. The new working directory is linked to the current
 repository, sharing everything except working directory specific files
 such as HEAD, index, etc. If `<path>` already exists, it must be empty.
++
+If `<branch>` is omitted and neither `-b` nor `-B` used, then, as a
+convenience, a new branch rooted at HEAD is created automatically, as if
+`-b $(basename <path>)` was specified.
 
 prune::
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index bf634a6..c8c6fa7 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -286,12 +286,16 @@ static int add(int ac, const char **av, const char *prefix)
 		die(_("-b and -B are mutually exclusive"));
 	if (ac < 1 || ac > 2)
 		usage_with_options(worktree_usage, options);
-	if (ac < 2 && !new_branch && !new_branch_force)
-		usage_with_options(worktree_usage, options);
 
 	path = prefix ? prefix_filename(prefix, strlen(prefix), av[0]) : av[0];
 	branch = ac < 2 ? "HEAD" : av[1];
 
+	if (ac < 2 && !new_branch && !new_branch_force) {
+		int n;
+		const char *s = worktree_basename(path, &n);
+		new_branch = xstrndup(s, n);
+	}
+
 	argv_array_push(&cmd, "checkout");
 	if (force)
 		argv_array_push(&cmd, "--ignore-other-worktrees");
diff --git a/t/t2025-worktree-add.sh b/t/t2025-worktree-add.sh
index 95a1141..59d73ff 100755
--- a/t/t2025-worktree-add.sh
+++ b/t/t2025-worktree-add.sh
@@ -147,4 +147,11 @@ test_expect_success '"add -b" with <branch> omitted' '
 	test_cmp expected actual
 '
 
+test_expect_success '"add" with <branch> omitted' '
+	git rev-parse HEAD >expected &&
+	git worktree add wiffle/bat &&
+	git rev-parse bat >actual &&
+	test_cmp expected actual
+'
+
 test_done
-- 
2.5.0.rc1.197.g417e668