worktree add: introduce "try --orphan" hint

Add a new advice/hint in `git worktree add` for when the user
tries to create a new worktree from a reference that doesn't exist.

Current Behavior:

% git init foo
Initialized empty Git repository in /path/to/foo/
% touch file
% git -C foo commit -q -a -m "test commit"
% git -C foo switch --orphan norefbranch
% git -C foo worktree add newbranch/
Preparing worktree (new branch 'newbranch')
fatal: invalid reference: HEAD
%

New Behavior:

% git init --bare foo
Initialized empty Git repository in /path/to/foo/
% touch file
% git -C foo commit -q -a -m "test commit"
% git -C foo switch --orphan norefbranch
% git -C foo worktree add newbranch/
Preparing worktree (new branch 'newbranch')
hint: If you meant to create a worktree containing a new orphan branch
hint: (branch with no commits) for this repository, you can do so
hint: using the --orphan option:
hint:
hint:   git worktree add --orphan newbranch/
hint:
hint: Disable this message with "git config advice.worktreeAddOrphan false"
fatal: invalid reference: HEAD
% git -C foo worktree add -b newbranch2 new_wt/
Preparing worktree (new branch 'newbranch')
hint: If you meant to create a worktree containing a new orphan branch
hint: (branch with no commits) for this repository, you can do so
hint: using the --orphan option:
hint:
hint:   git worktree add --orphan -b newbranch2 new_wt/
hint:
hint: Disable this message with "git config advice.worktreeAddOrphan false"
fatal: invalid reference: HEAD
%

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

1 files changed, 37 insertions, 0 deletions

diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index fba90582b6..46eef26179 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -401,6 +401,43 @@ test_expect_success '"add" worktree with orphan branch, lock, and reason' '
 	test_cmp expect .git/worktrees/orphan-with-lock-reason/locked
 '
 
+# Note: Quoted arguments containing spaces are not supported.
+test_wt_add_orphan_hint () {
+	local context="$1" &&
+	local use_branch=$2 &&
+	shift 2 &&
+	local opts="$*" &&
+	test_expect_success "'worktree add' show orphan hint in bad/orphan HEAD w/ $context" '
+		test_when_finished "rm -rf repo" &&
+		git init repo &&
+		(cd repo && test_commit commit) &&
+		git -C repo switch --orphan noref &&
+		test_must_fail git -C repo worktree add $opts foobar/ 2>actual &&
+		! grep "error: unknown switch" actual &&
+		grep "hint: If you meant to create a worktree containing a new orphan branch" actual &&
+		if [ $use_branch -eq 1 ]
+		then
+			grep -E "^hint:\s+git worktree add --orphan -b \S+ \S+\s*$" actual
+		else
+			grep -E "^hint:\s+git worktree add --orphan \S+\s*$" actual
+		fi
+
+	'
+}
+
+test_wt_add_orphan_hint 'no opts' 0
+test_wt_add_orphan_hint '-b' 1 -b foobar_branch
+test_wt_add_orphan_hint '-B' 1 -B foobar_branch
+
+test_expect_success "'worktree add' doesn't show orphan hint in bad/orphan HEAD w/ --quiet" '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(cd repo && test_commit commit) &&
+	test_must_fail git -C repo worktree add --quiet foobar_branch foobar/ 2>actual &&
+	! grep "error: unknown switch" actual &&
+	! grep "hint: If you meant to create a worktree containing a new orphan branch" actual
+'
+
 test_expect_success 'local clone from linked checkout' '
 	git clone --local here here-clone &&
 	( cd here-clone && git fsck )