Fix 'd' command in 'query-replace' in buffers not visiting files

* lisp/vc/diff.el (diff-file-local-copy): Use proper coding-system
when writing a local copy of a non-file visiting buffer.

* lisp/misearch.el (coding-system--for-buffer-diff): New variable.
(multi-file-replace-as-diff): Bind it to 'utf-8-emacs'.
(multi-file-diff-no-select): Use proper coding-system when reading
output of Diff.  (Bug#79761)

2 files changed, 16 insertions, 3 deletions

diff --git a/lisp/misearch.el b/lisp/misearch.el
index c20b75bf6f0..28cda1fcbf0 100644
--- a/lisp/misearch.el
+++ b/lisp/misearch.el
@@ -406,6 +406,9 @@ modified buffer to be able to use unsaved changes."
 (declare-function diff-setup-whitespace "diff-mode" ())
 (declare-function diff-setup-buffer-type "diff-mode" ())
 
+(defvar coding-system--for-buffer-diff nil
+  "Used to pass encoding down to callees of `multi-file-diff-no-select'.")
+
 ;;;###autoload
 (defun multi-file-replace-as-diff (files from-string replacements regexp-flag delimited-flag)
   "Show as diffs replacements of FROM-STRING with REPLACEMENTS.
@@ -439,7 +442,11 @@ as in `perform-replace'."
                   file-name
                 (when (or (not file-exists)
                           (eq multi-file-diff-unsaved 'use-modified-buffer))
-                  (find-buffer-visiting file-name)))))
+                  (find-buffer-visiting file-name))))
+             ;; Make sure any supported characters can be written to a
+             ;; file without asking the user to select a safe
+             ;; coding-system.
+             (coding-system--for-buffer-diff 'utf-8-emacs))
         (when non-file-buffer (setq file-name (buffer-name file-name)))
         (when (or file-exists file-buffer)
           (with-temp-buffer
@@ -540,7 +547,9 @@ specify labels to use for file names."
                                         (or new-alt new)))))
                      " ")))
     (with-current-buffer buf
-      (let ((inhibit-read-only t))
+      (let ((inhibit-read-only t)
+            (coding-system-for-read (or coding-system--for-buffer-diff
+                                        coding-system-for-read)))
         (insert command "\n")
         (call-process shell-file-name nil buf nil
                       shell-command-switch command))
diff --git a/lisp/vc/diff.el b/lisp/vc/diff.el
index c8a1b7c0efa..9e4a5349fef 100644
--- a/lisp/vc/diff.el
+++ b/lisp/vc/diff.el
@@ -118,13 +118,17 @@ Non-interactively, OLD and NEW may each be a file or a buffer."
   (display-buffer
    (diff-no-select old new switches no-async)))
 
+(defvar coding-system--for-buffer-diff) ; from misearch.el
+
 (defun diff-file-local-copy (file-or-buf)
   "Like `file-local-copy' but also supports a buffer as the argument.
 When FILE-OR-BUF is a buffer, return the filename of a local
 temporary file with the buffer's contents."
   (if (bufferp file-or-buf)
       (with-current-buffer file-or-buf
-        (let ((tempfile (make-temp-file "buffer-content-")))
+        (let ((tempfile (make-temp-file "buffer-content-"))
+              (coding-system-for-write (or coding-system--for-buffer-diff
+                                           coding-system-for-write)))
           (if diff-entire-buffers
               (write-region nil nil tempfile nil 'nomessage)
             (write-region (point-min) (point-max) tempfile nil 'nomessage))