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, 95 insertions, 0 deletions

diff --git a/builtin/prune.c b/builtin/prune.c
index 04d3b12ae4..f08670a984 100644
--- a/builtin/prune.c
+++ b/builtin/prune.c
@@ -76,6 +76,91 @@ static int prune_subdir(int nr, const char *path, void *data)
 	return 0;
 }
 
+static int prune_worktree(const char *id, struct strbuf *reason)
+{
+	struct stat st;
+	char *path;
+	int fd, len;
+
+	if (!is_directory(git_path("worktrees/%s", id))) {
+		strbuf_addf(reason, _("Removing worktrees/%s: not a valid directory"), id);
+		return 1;
+	}
+	if (file_exists(git_path("worktrees/%s/locked", id)))
+		return 0;
+	if (stat(git_path("worktrees/%s/gitdir", id), &st)) {
+		strbuf_addf(reason, _("Removing worktrees/%s: gitdir file does not exist"), id);
+		return 1;
+	}
+	fd = open(git_path("worktrees/%s/gitdir", id), O_RDONLY);
+	if (fd < 0) {
+		strbuf_addf(reason, _("Removing worktrees/%s: unable to read gitdir file (%s)"),
+			    id, strerror(errno));
+		return 1;
+	}
+	len = st.st_size;
+	path = xmalloc(len + 1);
+	read_in_full(fd, path, len);
+	close(fd);
+	while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))
+		len--;
+	if (!len) {
+		strbuf_addf(reason, _("Removing worktrees/%s: invalid gitdir file"), id);
+		free(path);
+		return 1;
+	}
+	path[len] = '\0';
+	if (!file_exists(path)) {
+		struct stat st_link;
+		free(path);
+		/*
+		 * the repo is moved manually and has not been
+		 * accessed since?
+		 */
+		if (!stat(git_path("worktrees/%s/link", id), &st_link) &&
+		    st_link.st_nlink > 1)
+			return 0;
+		strbuf_addf(reason, _("Removing worktrees/%s: gitdir file points to non-existent location"), id);
+		return 1;
+	}
+	free(path);
+	return st.st_mtime <= expire;
+}
+
+static void prune_worktrees(void)
+{
+	struct strbuf reason = STRBUF_INIT;
+	struct strbuf path = STRBUF_INIT;
+	DIR *dir = opendir(git_path("worktrees"));
+	struct dirent *d;
+	int ret;
+	if (!dir)
+		return;
+	while ((d = readdir(dir)) != NULL) {
+		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
+			continue;
+		strbuf_reset(&reason);
+		if (!prune_worktree(d->d_name, &reason))
+			continue;
+		if (show_only || verbose)
+			printf("%s\n", reason.buf);
+		if (show_only)
+			continue;
+		strbuf_reset(&path);
+		strbuf_addstr(&path, git_path("worktrees/%s", d->d_name));
+		ret = remove_dir_recursively(&path, 0);
+		if (ret < 0 && errno == ENOTDIR)
+			ret = unlink(path.buf);
+		if (ret)
+			error(_("failed to remove: %s"), strerror(errno));
+	}
+	closedir(dir);
+	if (!show_only)
+		rmdir(git_path("worktrees"));
+	strbuf_release(&reason);
+	strbuf_release(&path);
+}
+
 /*
  * Write errors (particularly out of space) can result in
  * failed temporary packs (and more rarely indexes and other
@@ -102,10 +187,12 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info revs;
 	struct progress *progress = NULL;
+	int do_prune_worktrees = 0;
 	const struct option options[] = {
 		OPT__DRY_RUN(&show_only, N_("do not remove, show only")),
 		OPT__VERBOSE(&verbose, N_("report pruned objects")),
 		OPT_BOOL(0, "progress", &show_progress, N_("show progress")),
+		OPT_BOOL(0, "worktrees", &do_prune_worktrees, N_("prune .git/worktrees")),
 		OPT_EXPIRY_DATE(0, "expire", &expire,
 				N_("expire objects older than <time>")),
 		OPT_END()
@@ -118,6 +205,14 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 	init_revisions(&revs, prefix);
 
 	argc = parse_options(argc, argv, prefix, options, prune_usage, 0);
+
+	if (do_prune_worktrees) {
+		if (argc)
+			die(_("--worktrees does not take extra arguments"));
+		prune_worktrees();
+		return 0;
+	}
+
 	while (argc--) {
 		unsigned char sha1[20];
 		const char *name = *argv++;