bug#50572: 28.0.50; [PATCH] fix VC to find the responsible backend with the most specific path.

[Manuel Giraud <manuel@ledu-giraud.fr>]

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When calling 'vc-next-action' on an unregistered file, VC could choose a
backend that is very far above this file in the directory hierarchy.

In my case, it chooses SVN as backend (because I have one in my homedir)
but I wanted it to choose the Git backend of the directory this file
resides.

This patch solves this issue by selecting the backend with the most
specific (in fact, the longest string) path to the file.


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From 9e673edc28f84a75f3bf0f53e7fba01c2f50e51c Mon Sep 17 00:00:00 2001
From: Manuel Giraud <manuel@ledu-giraud.fr>
Date: Mon, 13 Sep 2021 17:31:31 +0200
Subject: [PATCH] let VC find a responsible backend with the most specific
 path.

---
 lisp/vc/vc.el | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 4fcba65ab4..7160c98820 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -937,11 +937,16 @@ vc-backend-for-registration
 use."
   (catch 'found
     ;; First try: find a responsible backend, it must be a backend
-    ;; under which FILE is not yet registered.
-    (dolist (backend vc-handled-backends)
-      (and (not (vc-call-backend backend 'registered file))
-	   (vc-call-backend backend 'responsible-p file)
-	   (throw 'found backend)))
+    ;; under which FILE is not yet registered and with the most
+    ;; specific path to FILE.
+    (let ((max 0) bk)
+      (dolist (backend vc-handled-backends)
+        (when (not (vc-call-backend backend 'registered file))
+          (let* ((path (vc-call-backend backend 'responsible-p file))
+                 (len (length path)))
+            (when (and len (> len max))
+              (setq max len bk backend)))))
+      (when bk (throw 'found bk)))
     ;; no responsible backend
     (let* ((possible-backends
 	    (let (pos)
-- 
2.33.0


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In GNU Emacs 28.0.50 (build 1, x86_64-unknown-openbsd7.0, X toolkit, cairo version 1.16.0, Xaw3d scroll bars)
 of 2021-09-13 built on elite.giraud
Repository revision: 5ee05fa75d517fdd13c9795aa78e12489140e388
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-- 
Manuel Giraud