bug#81411: 31.0.90; Selecting completion for completing-read-multiple does not respect completion boundaries

From 4fd9ff48493f40f1e256f889bf7edf6a01559e6b Mon Sep 17 00:00:00 2001
From: "Aaron L. Zeng" <[email protected]>
Date: Thu, 13 Aug 2026 17:25:06 -0400
Subject: [PATCH] Fix choose-completion in CRM with boundaries

* lisp/emacs-lisp/crm.el (crm--choose-completion-string): Delete.
(completing-read-multiple): Set buffer-local
completion-no-auto-exit instead of using
choose-completion-string-functions.  Do not set
completion-list-insert-choice-function.

* test/lisp/emacs-lisp/crm-tests.el: New tests for completing-read-multiple.
---
 lisp/emacs-lisp/crm.el            |  27 +-------
 test/lisp/emacs-lisp/crm-tests.el | 103 ++++++++++++++++++++++++++++++
 2 files changed, 104 insertions(+), 26 deletions(-)
 create mode 100644 test/lisp/emacs-lisp/crm-tests.el

diff --git a/lisp/emacs-lisp/crm.el b/lisp/emacs-lisp/crm.el
index b68d3d55525..f94f079779b 100644
--- a/lisp/emacs-lisp/crm.el
+++ b/lisp/emacs-lisp/crm.el
@@ -217,17 +217,6 @@ crm-complete-and-exit
       (goto-char (match-end 0)))
     (if doexit (exit-minibuffer))))
 
-(defun crm--choose-completion-string (choice buffer base-position
-                                             &rest _ignored)
-  "Completion string chooser for `completing-read-multiple'.
-This is called from `choose-completion-string-functions'.
-It replaces the string that is currently being completed, without
-exiting the minibuffer."
-  (let ((completion-no-auto-exit t)
-        (choose-completion-string-functions nil))
-    (choose-completion-string choice buffer base-position)
-    t))
-
 ;; superemulates behavior of completing_read in src/minibuf.c
 ;; Use \\<crm-local-completion-map> so that help-enable-autoload can
 ;; do its thing.  Any keymap that is defined will do.
@@ -259,21 +248,7 @@ completing-read-multiple
          input)
     (minibuffer-with-setup-hook
         (lambda ()
-          (add-hook 'choose-completion-string-functions
-                    'crm--choose-completion-string nil 'local)
-          (setq-local completion-list-insert-choice-function
-                      (lambda (_start _end choice)
-                        (let* ((beg (save-excursion
-                                      (if (search-backward-regexp crm-separator
-                                                                  (field-beginning)
-                                                                  t)
-                                          (1+ (point))
-                                        (minibuffer-prompt-end))))
-                               (end (save-excursion
-                                      (if (search-forward-regexp crm-separator nil t)
-                                          (1- (point))
-                                        (point-max)))))
-                          (completion--replace beg end choice))))
+          (setq-local completion-no-auto-exit t)
           (setq-local crm-completion-table table)
           (use-local-map map))
       (setq input (completing-read
diff --git a/test/lisp/emacs-lisp/crm-tests.el b/test/lisp/emacs-lisp/crm-tests.el
new file mode 100644
index 00000000000..56b662d4a33
--- /dev/null
+++ b/test/lisp/emacs-lisp/crm-tests.el
@@ -0,0 +1,103 @@
+;;; crm-tests.el --- Tests for crm.el  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026-2026 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+
+(require 'crm)
+(require 'ert)
+
+;; Copied from minibuffer-tests.el
+(defmacro with-minibuffer-setup (completing-read &rest body)
+  (declare (indent 1) (debug t))
+  `(catch 'result
+     (minibuffer-with-setup-hook
+         (lambda ()
+           (let ((redisplay-skip-initial-frame nil)
+                 (executing-kbd-macro nil)) ; Don't skip redisplay
+             (throw 'result (progn . ,body))))
+       (let ((executing-kbd-macro t)) ; Force the real minibuffer
+         ,completing-read))))
+
+(defmacro crm-test-with-file-name-table (initial-input &rest body)
+  (declare (indent 1) (debug t))
+  `(let* ((root (make-temp-file "crm-boundary-" 'directory))
+          (default-directory root))
+     (unwind-protect
+         (progn
+           (make-directory "dir")
+           (make-directory "dir/subdir")
+           (with-temp-file "dir/alpha" (insert ""))
+           (with-temp-file "dir/beta" (insert ""))
+           (with-temp-file "dir/subdir/gamma" (insert ""))
+           (with-minibuffer-setup
+               (completing-read-multiple "Pick: "
+                                         #'completion-file-name-table
+                                         nil t ,initial-input)
+             ,@body))
+       (delete-directory root t))))
+
+(ert-deftest crm-test-complete-uses-boundaries ()
+  (crm-test-with-file-name-table "dir/a"
+    (save-excursion (insert ",d/b"))
+    (should (equal (minibuffer-contents) "dir/a,d/b"))
+    (execute-kbd-macro (kbd "TAB"))
+    (should (equal (minibuffer-contents) "dir/alpha,d/b"))
+    ;; complete between d and /
+    (execute-kbd-macro (kbd "C-f C-f TAB"))
+    (should (equal (minibuffer-contents) "dir/alpha,dir/b"))
+    (execute-kbd-macro (kbd "C-e TAB"))
+    (should (equal (minibuffer-contents) "dir/alpha,dir/beta"))
+    (execute-kbd-macro (kbd ", d/s/g TAB"))
+    (should (equal (minibuffer-contents) "dir/alpha,dir/beta,dir/subdir/gamma"))))
+
+(ert-deftest crm-test-choose-completion-uses-boundaries ()
+  "Regression test for Bug#81411."
+  (crm-test-with-file-name-table "dir/a"
+    (save-excursion (insert ",d/b"))
+    (should (equal (minibuffer-contents) "dir/a,d/b"))
+    (execute-kbd-macro (kbd "? M-<down> M-RET"))
+    (should (equal (minibuffer-contents) "dir/alpha,d/b"))
+    ;; complete between d and /
+    (execute-kbd-macro (kbd "C-f C-f ? M-<down> M-RET"))
+    (should (equal (minibuffer-contents) "dir/alpha,dir/b"))
+    (execute-kbd-macro (kbd "C-e ? M-<down> M-RET"))
+    (should (equal (minibuffer-contents) "dir/alpha,dir/beta"))
+    (execute-kbd-macro (kbd ", d/s/g ? M-<down> M-RET"))
+    (should (equal (minibuffer-contents) "dir/alpha,dir/beta,dir/subdir/gamma"))))
+
+(ert-deftest crm-test-choose-completion-multi-char-separator ()
+  "Regression test for Bug#81411."
+  (crm-test-with-file-name-table "dir/a"
+    (save-excursion (insert " ,  d/b"))
+    (should (equal (minibuffer-contents) "dir/a ,  d/b"))
+    (execute-kbd-macro (kbd "? M-<down> M-RET"))
+    (should (equal (minibuffer-contents) "dir/alpha ,  d/b"))
+    ;; complete between d and /
+    (forward-char 5)
+    (execute-kbd-macro (kbd "? M-<down> M-RET"))
+    (should (equal (minibuffer-contents) "dir/alpha ,  dir/b"))
+    (execute-kbd-macro (kbd "C-e ? M-<down> M-RET"))
+    (should (equal (minibuffer-contents) "dir/alpha ,  dir/beta"))))
+
+(provide 'crm-tests)
+;;; crm-tests.el ends here
-- 
2.43.7