bug#66187: read-file-name unexpected behavior when MUSTMATCH is a function

[Joseph Turner]

Ping!  I hope a fix like this can be merged into Emacs 29 still :)

>From 609bf4964f88b01f4843e29b2cf71ee1cd2f6125 Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Sun, 12 Nov 2023 13:21:50 -0800
Subject: [PATCH] Fix completing-read functional REQUIRE-MATCH behavior

* lisp/minibuffer.el (completion--complete-and-exit): If
minibuffer-completion-confirm is a function which returns nil,
immediately fail to complete.

See bug#66187.
---
 lisp/minibuffer.el | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 3e30b68d5e9..9fad3e71fad 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -1847,10 +1847,13 @@ appear to be a match."
    ;; Allow user to specify null string
    ((= beg end) (funcall exit-function))
    ;; The CONFIRM argument is a predicate.
-   ((and (functionp minibuffer-completion-confirm)
-         (funcall minibuffer-completion-confirm
-                  (buffer-substring beg end)))
-    (funcall exit-function))
+   ((functionp minibuffer-completion-confirm)
+    (if (funcall minibuffer-completion-confirm
+                 (buffer-substring beg end))
+        (funcall exit-function)
+      (unless completion-fail-discreetly
+       (ding)
+       (completion--message "No match"))))
    ;; See if we have a completion from the table.
    ((test-completion (buffer-substring beg end)
                      minibuffer-completion-table
-- 
2.41.0

Thank you!

Joseph