worktree: teach `list` to annotate locked worktree

The "git worktree list" shows the absolute path to the working tree,
the commit that is checked out and the name of the branch. It is not
immediately obvious which of the worktrees, if any, are locked.

"git worktree remove" refuses to remove a locked worktree with
an error message. If "git worktree list" told which worktrees
are locked in its output, the user would not even attempt to
remove such a worktree, or would realize that
"git worktree remove -f -f <path>" is required.

Teach "git worktree list" to append "locked" to its output.
The output from the command becomes like so:

    $ git worktree list
    /path/to/main             abc123 [master]
    /path/to/worktree         456def (detached HEAD)
    /path/to/locked-worktree  123abc (detached HEAD) locked

Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Rafael Silva <rafaeloliveira.cs@gmail.com>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-worktree.txt

@@ -96,8 +96,9 @@ list::
 
 List details of each working tree.  The main working tree is listed first,
 followed by each of the linked working trees.  The output details include
-whether the working tree is bare, the revision currently checked out, and the
-branch currently checked out (or "detached HEAD" if none).
+whether the working tree is bare, the revision currently checked out, the
+branch currently checked out (or "detached HEAD" if none), and "locked" if
+the worktree is locked.
 
 lock::
 

builtin/worktree.c

@@ -676,8 +676,11 @@ static void show_worktree(struct worktree *wt, int path_maxlen, int abbrev_len)
 		} else
 			strbuf_addstr(&sb, "(error)");
 	}
-	printf("%s\n", sb.buf);
 
+	if (!is_main_worktree(wt) && worktree_lock_reason(wt))
+		strbuf_addstr(&sb, " locked");
+
+	printf("%s\n", sb.buf);
 	strbuf_release(&sb);
 }
 

t/t2402-worktree-list.sh

@@ -61,6 +61,16 @@ test_expect_success '"list" all worktrees --porcelain' '
 	test_cmp expect actual
 '
 
+test_expect_success '"list" all worktress with locked annotation' '
+	test_when_finished "rm -rf locked unlocked out && git worktree prune" &&
+	git worktree add --detach locked master &&
+	git worktree add --detach unlocked master &&
+	git worktree lock locked &&
+	git worktree list >out &&
+	grep "/locked  *[0-9a-f].* locked$" out &&
+	! grep "/unlocked  *[0-9a-f].* locked$" out
+'
+
 test_expect_success 'bare repo setup' '
 	git init --bare bare1 &&
 	echo "data" >file1 &&