worktree: teach "repair" to fix outgoing links to worktrees

The .git/worktrees/<id>/gitdir file points at the location of a linked
worktree's .git file. Its content must be of the form
/path/to/worktree/.git (from which the location of the worktree itself
can be derived by stripping the "/.git" suffix). If the gitdir file is
deleted or becomes corrupted or outdated, then Git will be unable to
find the linked worktree. An easy way for the gitdir file to become
outdated is for the user to move the worktree manually (without using
"git worktree move"). Although it is possible to manually update the
gitdir file to reflect the new linked worktree location, doing so
requires a level of knowledge about worktree internals beyond what a
user should be expected to know offhand.

Therefore, teach "git worktree repair" how to repair broken or outdated
.git/worktrees/<id>/gitdir files automatically. (For this to work, the
command must either be invoked from within the worktree whose gitdir
file requires repair, or from within the main or any linked worktree by
providing the path of the broken worktree as an argument to "git
worktree repair".)

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 74 insertions, 0 deletions

diff --git a/worktree.c b/worktree.c
index 3ad93cc4aa..46a5fb8447 100644
--- a/worktree.c
+++ b/worktree.c
@@ -632,3 +632,77 @@ void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 		repair_gitfile(*wt, fn, cb_data);
 	free_worktrees(worktrees);
 }
+
+static int is_main_worktree_path(const char *path)
+{
+	struct strbuf target = STRBUF_INIT;
+	struct strbuf maindir = STRBUF_INIT;
+	int cmp;
+
+	strbuf_add_real_path(&target, path);
+	strbuf_strip_suffix(&target, "/.git");
+	strbuf_add_real_path(&maindir, get_git_common_dir());
+	strbuf_strip_suffix(&maindir, "/.git");
+	cmp = fspathcmp(maindir.buf, target.buf);
+
+	strbuf_release(&maindir);
+	strbuf_release(&target);
+	return !cmp;
+}
+
+/*
+ * Repair <repo>/worktrees/<id>/gitdir if missing, corrupt, or not pointing at
+ * the worktree's path.
+ */
+void repair_worktree_at_path(const char *path,
+			     worktree_repair_fn fn, void *cb_data)
+{
+	struct strbuf dotgit = STRBUF_INIT;
+	struct strbuf realdotgit = STRBUF_INIT;
+	struct strbuf gitdir = STRBUF_INIT;
+	struct strbuf olddotgit = STRBUF_INIT;
+	char *backlink = NULL;
+	const char *repair = NULL;
+	int err;
+
+	if (!fn)
+		fn = repair_noop;
+
+	if (is_main_worktree_path(path))
+		goto done;
+
+	strbuf_addf(&dotgit, "%s/.git", path);
+	if (!strbuf_realpath(&realdotgit, dotgit.buf, 0)) {
+		fn(1, path, _("not a valid path"), cb_data);
+		goto done;
+	}
+
+	backlink = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
+	if (err == READ_GITFILE_ERR_NOT_A_FILE) {
+		fn(1, realdotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
+		goto done;
+	} else if (err) {
+		fn(1, realdotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
+		goto done;
+	}
+
+	strbuf_addf(&gitdir, "%s/gitdir", backlink);
+	if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
+		repair = _("gitdir unreadable");
+	else {
+		strbuf_rtrim(&olddotgit);
+		if (fspathcmp(olddotgit.buf, realdotgit.buf))
+			repair = _("gitdir incorrect");
+	}
+
+	if (repair) {
+		fn(0, gitdir.buf, repair, cb_data);
+		write_file(gitdir.buf, "%s", realdotgit.buf);
+	}
+done:
+	free(backlink);
+	strbuf_release(&olddotgit);
+	strbuf_release(&gitdir);
+	strbuf_release(&realdotgit);
+	strbuf_release(&dotgit);
+}