bug#63949: 30.0.50; `vc-print-log´ does not erase buffer when called from *vc-change-log* buffer, at least for CVS logs

[Dmitry Gutov <dmitry@gutov.dev>]

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On 21/06/2023 18:30, Eli Zaretskii wrote:
>> Date: Wed, 21 Jun 2023 17:37:55 +0300
>> Cc:63949@debbugs.gnu.org, Jens Schmidt<jschmidt4gnu@vodafonemail.de>
>> From: Dmitry Gutov<dmitry@gutov.dev>
>>
>> On 21/06/2023 16:03, Jens Schmidt wrote:
>>> Tested on emacs-29.
>> Excellent, thank you.
>>
>> Eli, I suggest we push it to emacs-29 now.
> Fine by me, thanks.

And done.

>> There could be ways to make it prettier, but probably not by much -- at
>> least I don't see any obvious ones if we're keeping the indirect
>> buffer-related functionality. Anyway, we can look into that later in
>> Emacs 30.
> Right.

I'm attaching a patch which should work fine, though could be a tad 
risky for 29.

Jens (and possibly others), could you try it out?

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diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index 410fe5c01e1..24e786eb218 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -1121,19 +1121,8 @@ vc-deduce-fileset
 the returned list.
 
 BEWARE: this function may change the current buffer."
-  (let (new-buf res)
-    (with-current-buffer (or (buffer-base-buffer) (current-buffer))
-      (setq res
-            (vc-deduce-fileset-1 not-state-changing
-                                 allow-unregistered
-                                 state-model-only-files))
-      (setq new-buf (current-buffer)))
-    (set-buffer new-buf)
-    res))
-
-(defun vc-deduce-fileset-1 (not-state-changing
-                            allow-unregistered
-                            state-model-only-files)
+  (when (buffer-base-buffer)
+    (set-buffer (buffer-base-buffer)))
   (let (backend)
     (cond
      ((derived-mode-p 'vc-dir-mode)
@@ -1158,7 +1147,7 @@ vc-deduce-fileset-1
 				      (derived-mode-p 'diff-mode)))))
       (progn                  ;FIXME: Why not `with-current-buffer'? --Stef.
 	(set-buffer vc-parent-buffer)
-	(vc-deduce-fileset-1 not-state-changing allow-unregistered state-model-only-files)))
+	(vc-deduce-fileset not-state-changing allow-unregistered state-model-only-files)))
      ((and (not buffer-file-name)
 	   (setq backend (vc-responsible-backend default-directory)))
       (list backend nil))