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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Lars Ingebrigtsen <larsi@gnus.org> writes:

> Manuel Giraud <manuel@ledu-giraud.fr> writes:
>
>> I thought that we might already have a function for this. Does counting
>> slashes will work with Windows path?
>
> Hm...  Actually, I'm not sure.  Perhaps doing a series of
> file-name-directory/directory-file-name in a loop (to peel off the
> directory components) would be the best algorithm here?  And I don't
> think we have a function for this -- at least I can't find anything
> promising while poking around.

That was what I found also inspired from dired-up-directory. So here is
what I've done. What bothers me is that it introduce two general purpose
(and probably buggy) functions that should reside somewhere else IMO.


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From 326c4c0f2f087a1be75657425a362aa05fc47557 Mon Sep 17 00:00:00 2001
From: Manuel Giraud <manuel@ledu-giraud.fr>
Date: Tue, 9 Nov 2021 09:44:26 +0100
Subject: [PATCH] Use file depth for most specific path in
 vc-backend-for-registration

---
 lisp/vc/vc.el | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index c9500f454a..70c9434a20 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -927,6 +927,15 @@ with-vc-properties
                   property (cdr setting))))))))
 
 ;;; Code for deducing what fileset and backend to assume
+(defun parent-directory (filename)
+  (file-name-directory (directory-file-name filename)))
+
+(defun file-depth (filename)
+  (cl-loop for oparent = nil then parent
+	   for parent = (parent-directory (expand-file-name filename)) then (parent-directory parent)
+	   for i from 0
+	   until (string= parent oparent)
+	   finally (return i)))
 
 (defun vc-backend-for-registration (file)
   "Return a backend that can be used for registering FILE.
@@ -944,9 +953,9 @@ vc-backend-for-registration
       (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)))))
+                 (depth (and path (file-depth path))))
+            (when (and depth (> depth max))
+              (setq max depth bk backend)))))
       (when bk
         (throw 'found bk)))
     ;; no responsible backend
-- 
2.33.1


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-- 
Manuel Giraud