Subject: bug#40919: 27.0.91; next-error-select-buffer does not always behave as documented

From: Juri Linkov <[email-masked]>
Date: Thu, 11 Jun 2020 02:05:39 +0300

>> Tho I think in master next-error-find-buffer-function
>> should support a list of functions, so the user could customize
>> their order to arrange their priorities.  Then they could be called
>> with run-hook-with-args-until-success.
>
> I suppose.
>
> We should perhaps wait and see if people do customize that variable at
> all. But the idea is solid.

Actually, people already want to customize it to a list (at least, I know one such user :)
So here is a patch:

diff --git a/lisp/simple.el b/lisp/simple.el
index 0fe8a1025c..646236879c 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -199,7 +199,7 @@ next-error-buffer-p
 	   (and extra-test-inclusive
 		(funcall extra-test-inclusive))))))
 
-(defcustom next-error-find-buffer-function #'ignore
+(defcustom next-error-find-buffer-function '(ignore)
   "Function called to find a `next-error' capable buffer.
 This functions takes the same three arguments as the function
 `next-error-find-buffer', and should return the buffer to be
@@ -208,12 +208,13 @@ next-error-find-buffer-function
 If the function returns nil, `next-error-find-buffer' will
 try to use the buffer it used previously, and failing that
 all other buffers."
-  :type '(choice (const :tag "No default" ignore)
-                 (const :tag "Single next-error capable buffer on selected frame"
-                        next-error-buffer-on-selected-frame)
-                 (const :tag "Current buffer if next-error capable and outside navigation"
-                        next-error-no-navigation-try-current)
-                 (function :tag "Other function"))
+  :type '(repeat
+          (choice (const :tag "No default" ignore)
+                  (const :tag "Single next-error capable buffer on selected frame"
+                         next-error-buffer-on-selected-frame)
+                  (const :tag "Current buffer if next-error capable and outside navigation"
+                         next-error-no-navigation-try-current)
+                  (function :tag "Other function")))
   :group 'next-error
   :version "28.1")
 
@@ -275,9 +276,13 @@ next-error-find-buffer
 that buffer is rejected."
   (or
    ;; 1. If a customizable function returns a buffer, use it.
-   (funcall next-error-find-buffer-function avoid-current
-                                            extra-test-inclusive
-                                            extra-test-exclusive)
+   (or (and (functionp next-error-find-buffer-function)
+            (funcall next-error-find-buffer-function avoid-current
+                     extra-test-inclusive extra-test-exclusive))
+       (and (listp next-error-find-buffer-function)
+            (run-hook-with-args-until-success
+             'next-error-find-buffer-function avoid-current
+             extra-test-inclusive extra-test-exclusive)))
    ;; 2. If next-error-last-buffer is an acceptable buffer, use that.
    (if (and next-error-last-buffer
             (next-error-buffer-p next-error-last-buffer avoid-current