worktree add: add --orphan flag

Add support for creating an orphan branch when adding a new worktree.
The functionality of this flag is equivalent to git switch's --orphan
option.

Current Behavior:
% git -C foo.git --no-pager branch -l
+ main
% git -C foo.git worktree add main/
Preparing worktree (new branch 'main')
HEAD is now at 6c93a75 a commit
%

% git init bar.git
Initialized empty Git repository in /path/to/bar.git/
% git -C bar.git --no-pager branch -l

% git -C bar.git worktree add main/
Preparing worktree (new branch 'main')
fatal: not a valid object name: 'HEAD'
%

New Behavior:

% git -C foo.git --no-pager branch -l
+ main
% git -C foo.git worktree add main/
Preparing worktree (new branch 'main')
HEAD is now at 6c93a75 a commit
%

% git init --bare bar.git
Initialized empty Git repository in /path/to/bar.git/
% git -C bar.git --no-pager branch -l

% git -C bar.git worktree add main/
Preparing worktree (new branch 'main')
fatal: invalid reference: HEAD
% git -C bar.git worktree add --orphan -b main/
Preparing worktree (new branch 'main')
% git -C bar.git worktree add --orphan -b newbranch worktreedir/
Preparing worktree (new branch 'newbranch')
%

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jacob Abel <jacobabel@nullpo.dev>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 68 insertions, 0 deletions

diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 841f15f59e..fba90582b6 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -312,6 +312,10 @@ test_wt_add_excl () {
 test_wt_add_excl -b poodle -B poodle bamboo main
 test_wt_add_excl -b poodle --detach bamboo main
 test_wt_add_excl -B poodle --detach bamboo main
+test_wt_add_excl --orphan --detach bamboo
+test_wt_add_excl --orphan --no-checkout bamboo
+test_wt_add_excl --orphan bamboo main
+test_wt_add_excl --orphan -b bamboo wtdir/ main
 
 test_expect_success '"add -B" fails if the branch is checked out' '
 	git rev-parse newmain >before &&
@@ -341,6 +345,62 @@ test_expect_success 'add --quiet -b' '
 	test_must_be_empty actual
 '
 
+test_expect_success '"add --orphan"' '
+	test_when_finished "git worktree remove -f -f orphandir" &&
+	git worktree add --orphan -b neworphan orphandir &&
+	echo refs/heads/neworphan >expected &&
+	git -C orphandir symbolic-ref HEAD >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '"add --orphan (no -b)"' '
+	test_when_finished "git worktree remove -f -f neworphan" &&
+	git worktree add --orphan neworphan &&
+	echo refs/heads/neworphan >expected &&
+	git -C neworphan symbolic-ref HEAD >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '"add --orphan --quiet"' '
+	test_when_finished "git worktree remove -f -f orphandir" &&
+	git worktree add --quiet --orphan -b neworphan orphandir 2>log.actual &&
+	test_must_be_empty log.actual &&
+	echo refs/heads/neworphan >expected &&
+	git -C orphandir symbolic-ref HEAD >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '"add --orphan" fails if the branch already exists' '
+	test_when_finished "git branch -D existingbranch" &&
+	git worktree add -b existingbranch orphandir main &&
+	git worktree remove orphandir &&
+	test_must_fail git worktree add --orphan -b existingbranch orphandir
+'
+
+test_expect_success '"add --orphan" with empty repository' '
+	test_when_finished "rm -rf empty_repo" &&
+	echo refs/heads/newbranch >expected &&
+	GIT_DIR="empty_repo" git init --bare &&
+	git -C empty_repo worktree add --orphan -b newbranch worktreedir &&
+	git -C empty_repo/worktreedir symbolic-ref HEAD >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '"add" worktree with orphan branch and lock' '
+	git worktree add --lock --orphan -b orphanbr orphan-with-lock &&
+	test_when_finished "git worktree unlock orphan-with-lock || :" &&
+	test -f .git/worktrees/orphan-with-lock/locked
+'
+
+test_expect_success '"add" worktree with orphan branch, lock, and reason' '
+	lock_reason="why not" &&
+	git worktree add --detach --lock --reason "$lock_reason" orphan-with-lock-reason main &&
+	test_when_finished "git worktree unlock orphan-with-lock-reason || :" &&
+	test -f .git/worktrees/orphan-with-lock-reason/locked &&
+	echo "$lock_reason" >expect &&
+	test_cmp expect .git/worktrees/orphan-with-lock-reason/locked
+'
+
 test_expect_success 'local clone from linked checkout' '
 	git clone --local here here-clone &&
 	( cd here-clone && git fsck )
@@ -457,6 +517,14 @@ setup_remote_repo () {
 	)
 }
 
+test_expect_success '"add" <path> <remote/branch> w/ no HEAD' '
+	test_when_finished rm -rf repo_upstream repo_local foo &&
+	setup_remote_repo repo_upstream repo_local &&
+	git -C repo_local config --bool core.bare true &&
+	git -C repo_local branch -D main &&
+	git -C repo_local worktree add ./foo repo_upstream/foo
+'
+
 test_expect_success '--no-track avoids setting up tracking' '
 	test_when_finished rm -rf repo_upstream repo_local foo &&
 	setup_remote_repo repo_upstream repo_local &&