Subject: Re: bug#42966: 28.0.50; vc-dir: wrong backend

From: Lars Ingebrigtsen <[email-masked]>
Date: Sun, 18 Oct 2020 10:26:39 +0200

Dmitry Gutov <[email-masked]> writes:

> Could you send an attachment?

Included here.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 39d0fab391..8def7da377 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -979,12 +979,22 @@ vc-responsible-backend
 If NO-ERROR is nil, signal an error that no VC backend is
 responsible for the given file."
   (or (and (not (file-directory-p file)) (vc-backend file))
-      (catch 'found
-	;; First try: find a responsible backend.  If this is for registration,
-	;; it must be a backend under which FILE is not yet registered.
-	(dolist (backend vc-handled-backends)
-	  (and (vc-call-backend backend 'responsible-p file)
-	       (throw 'found backend))))
+      ;; First try: find a responsible backend.  If this is for registration,
+      ;; it must be a backend under which FILE is not yet registered.
+      (let ((dirs (delq nil
+                        (mapcar
+                         (lambda (backend)
+                           (when-let ((dir (vc-call-backend
+                                            backend 'responsible-p file)))
+                             (cons backend dir)))
+                         vc-handled-backends))))
+        ;; Just a single response (or none); use it.
+        (if (< (length dirs) 2)
+            (caar dirs)
+          ;; Several roots; we seem to have one vc inside another's
+          ;; directory.  Choose the most specific.
+          (caar (sort dirs (lambda (d1 d2)
+                             (< (length (cdr d2)) (length (cdr d1))))))))
       (unless no-error
         (error "No VC backend is responsible for %s" file))))