worktree: stop supporting moving worktrees manually

The current update_linked_gitdir() has a bug that can create "gitdir"
file in non-multi-worktree setup. Worse, sometimes it can write relative
path to "gitdir" file, which will not work (e.g. "git worktree list"
will display the worktree's location incorrectly)

Instead of fixing this, we step back a bit. The original design was
probably not well thought out. For now, if the user manually moves a
worktree, they have to fix up "gitdir" file manually or the worktree
will get pruned.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-worktree.txt

@@ -32,11 +32,9 @@ The working tree's administrative files in the repository (see
 `git worktree prune` in the main or any linked working tree to
 clean up any stale administrative files.
 
-If you move a linked working tree to another file system, or
-within a file system that does not support hard links, you need to run
-at least one git command inside the linked working tree
-(e.g. `git status`) in order to update its administrative files in the
-repository so that they do not get automatically pruned.
+If you move a linked working tree, you need to manually update the
+administrative files so that they do not get pruned automatically. See
+section "DETAILS" for more information.
 
 If a linked working tree is stored on a portable device or network share
 which is not always mounted, you can prevent its administrative files from
@@ -137,6 +135,13 @@ thumb is do not make any assumption about whether a path belongs to
 $GIT_DIR or $GIT_COMMON_DIR when you need to directly access something
 inside $GIT_DIR. Use `git rev-parse --git-path` to get the final path.
 
+If you move a linked working tree, you need to update the 'gitdir' file
+in the entry's directory. For example, if a linked working tree is moved
+to `/newpath/test-next` and its `.git` file points to
+`/path/main/.git/worktrees/test-next`, then update
+`/path/main/.git/worktrees/test-next/gitdir` to reference `/newpath/test-next`
+instead.
+
 To prevent a $GIT_DIR/worktrees entry from being pruned (which
 can be useful in some situations, such as when the
 entry's working tree is stored on a portable device), add a file named

setup.c

@@ -401,17 +401,6 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 	return ret;
 }
 
-static void update_linked_gitdir(const char *gitfile, const char *gitdir)
-{
-	struct strbuf path = STRBUF_INIT;
-	struct stat st;
-
-	strbuf_addf(&path, "%s/gitdir", gitdir);
-	if (stat(path.buf, &st) || st.st_mtime + 24 * 3600 < time(NULL))
-		write_file(path.buf, "%s", gitfile);
-	strbuf_release(&path);
-}
-
 /*
  * Try to read the location of the git directory from the .git file,
  * return path to git directory if found.
@@ -481,7 +470,6 @@ const char *read_gitfile_gently(const char *path, int *return_error_code)
 		error_code = READ_GITFILE_ERR_NOT_A_REPO;
 		goto cleanup_return;
 	}
-	update_linked_gitdir(path, dir);
 	path = real_path(dir);
 
 cleanup_return: