prune: strategies for linked checkouts

(alias R=$GIT_COMMON_DIR/worktrees/<id>)

 - linked checkouts are supposed to keep its location in $R/gitdir up
   to date. The use case is auto fixup after a manual checkout move.

 - linked checkouts are supposed to update mtime of $R/gitdir. If
   $R/gitdir's mtime is older than a limit, and it points to nowhere,
   worktrees/<id> is to be pruned.

 - If $R/locked exists, worktrees/<id> is not supposed to be pruned. If
   $R/locked exists and $R/gitdir's mtime is older than a really long
   limit, warn about old unused repo.

 - "git checkout --to" is supposed to make a hard link named $R/link
   pointing to the .git file on supported file systems to help detect
   the user manually deleting the checkout. If $R/link exists and its
   link count is greated than 1, the repo is kept.

Helped-by: Marc Branchaud <marcnarc@xiplink.com>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/setup.c b/setup.c
index b99bdd30e6..fb6186049d 100644
--- a/setup.c
+++ b/setup.c
@@ -390,6 +390,17 @@ 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/gitfile", gitdir);
+	if (stat(path.buf, &st) || st.st_mtime + 24 * 3600 < time(NULL))
+		write_file(path.buf, 0, "%s\n", gitfile);
+	strbuf_release(&path);
+}
+
 /*
  * Try to read the location of the git directory from the .git file,
  * return path to git directory if found.
@@ -438,6 +449,8 @@ const char *read_gitfile(const char *path)
 
 	if (!is_git_directory(dir))
 		die("Not a git repository: %s", dir);
+
+	update_linked_gitdir(path, dir);
 	path = real_path(dir);
 
 	free(buf);