[PATCH 1/6] worktree.c: add validate_worktree()

[Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>]

This function is later used by "worktree move" and "worktree remove"
to ensure that we have a good connection between the repository and
the worktree. For example, if a worktree is moved manually, the
worktree location recorded in $GIT_DIR/worktrees/.../gitdir is
incorrect and we should not move that one.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
---
 worktree.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 worktree.h |  5 +++++
 2 files changed, 68 insertions(+)

diff --git a/worktree.c b/worktree.c
index eb61212..929072a 100644
--- a/worktree.c
+++ b/worktree.c
@@ -291,6 +291,69 @@ const char *is_worktree_locked(struct worktree *wt)
 	return wt->lock_reason;
 }
 
+static int report(int quiet, const char *fmt, ...)
+{
+	va_list params;
+
+	if (quiet)
+		return -1;
+
+	va_start(params, fmt);
+	vfprintf(stderr, fmt, params);
+	fputc('\n', stderr);
+	va_end(params);
+	return -1;
+}
+
+int validate_worktree(const struct worktree *wt, int quiet)
+{
+	struct strbuf sb = STRBUF_INIT;
+	const char *path;
+	int err;
+
+	if (is_main_worktree(wt)) {
+		/*
+		 * Main worktree using .git file to point to the
+		 * repository would make it impossible to know where
+		 * the actual worktree is if this function is executed
+		 * from another worktree. No .git file support for now.
+		 */
+		strbuf_addf(&sb, "%s/.git", wt->path);
+		if (!is_directory(sb.buf)) {
+			strbuf_release(&sb);
+			return report(quiet, _("'%s/.git' at main worktree is not the repository directory"),
+				      wt->path);
+		}
+		return 0;
+	}
+
+	/*
+	 * Make sure "gitdir" file points to a real .git file and that
+	 * file points back here.
+	 */
+	if (!is_absolute_path(wt->path))
+		return report(quiet, _("'%s' file does not contain absolute path to the worktree location"),
+			      git_common_path("worktrees/%s/gitdir", wt->id));
+
+	strbuf_addf(&sb, "%s/.git", wt->path);
+	if (!file_exists(sb.buf)) {
+		strbuf_release(&sb);
+		return report(quiet, _("'%s/.git' does not exist"), wt->path);
+	}
+
+	path = read_gitfile_gently(sb.buf, &err);
+	strbuf_release(&sb);
+	if (!path)
+		return report(quiet, _("'%s/.git' is not a .git file, error code %d"),
+			      wt->path, err);
+
+	if (fspathcmp(path, real_path(git_common_path("worktrees/%s", wt->id))))
+		return report(quiet, _("'%s' does not point back to"),
+			      wt->path, git_common_path("worktrees/%s", wt->id));
+
+	return 0;
+}
+
 int is_worktree_being_rebased(const struct worktree *wt,
 			      const char *target)
 {
diff --git a/worktree.h b/worktree.h
index d59ce1f..4433db2 100644
--- a/worktree.h
+++ b/worktree.h
@@ -52,6 +52,11 @@ extern int is_main_worktree(const struct worktree *wt);
  */
 extern const char *is_worktree_locked(struct worktree *wt);
 
+/*
+ * Return zero if the worktree is in good condition.
+ */
+extern int validate_worktree(const struct worktree *wt, int quiet);
+
 /*
  * Free up the memory for worktree(s)
  */
-- 
2.8.2.524.g6ff3d78