* lisp/international/mule-cmds.el: Fix bug#38642

(universal-coding-system-argument): Adjust the code to the way
`universal-argument` works nowadays.  Handle `prefix-arg` a bit more
like `command_loop` does.

* test/lisp/international/mule-tests.el
(mule-cmds--test-universal-coding-system-argument): New test.

1 files changed, 18 insertions, 21 deletions

diff --git a/lisp/international/mule-cmds.el b/lisp/international/mule-cmds.el
index e4f5bb2a5f0..0a8a4aa6610 100644
--- a/lisp/international/mule-cmds.el
+++ b/lisp/international/mule-cmds.el
@@ -295,10 +295,14 @@ wrong, use this command again to toggle back to the right mode."
                 (format "Coding system for following command (default %s): " default)
               "Coding system for following command: ")
             default))))
+  ;; FIXME: This "read-key-sequence + call-interactively" loop is trying to
+  ;; reproduce the normal command loop, but this "can't" be done faithfully so
+  ;; it necessarily suffers from breakage in corner cases (e.g. it fails to run
+  ;; pre/post-command-hook, doesn't properly set this-command/last-command, it
+  ;; doesn't handle keyboard macros, ...).
   (let* ((keyseq (read-key-sequence
                   (format "Command to execute with %s:" coding-system)))
-         (cmd (key-binding keyseq))
-         prefix)
+         (cmd (key-binding keyseq)))
     ;; read-key-sequence ignores quit, so make an explicit check.
     (if (equal last-input-event (nth 3 (current-input-mode)))
         (keyboard-quit))
@@ -309,28 +313,21 @@ wrong, use this command again to toggle back to the right mode."
       (while (progn
                (setq keyseq (read-key-sequence nil t)
                      cmd (key-binding keyseq t))
-               (not (eq cmd 'universal-argument-other-key)))
-        (let ((current-prefix-arg prefix-arg)
-              ;; Have to bind `last-command-event' here so that
-              ;; `digit-argument', for instance, can compute the
-              ;; `prefix-arg'.
-              (last-command-event (aref keyseq 0)))
-          (call-interactively cmd)))
-
-      ;; This is the final call to `universal-argument-other-key', which
-      ;; sets the final `prefix-arg'.
-      (let ((current-prefix-arg prefix-arg))
-        (call-interactively cmd))
-
-      ;; Read the command to execute with the given `prefix-arg'.
-      (setq prefix prefix-arg
-            keyseq (read-key-sequence nil t)
-            cmd (key-binding keyseq)))
+               (memq cmd '(negative-argument digit-argument
+                           universal-argument-more)))
+        (setq current-prefix-arg prefix-arg prefix-arg nil)
+        ;; Have to bind `last-command-event' here so that
+        ;; `digit-argument', for instance, can compute the
+        ;; `prefix-arg'.
+        (setq last-command-event (aref keyseq 0))
+        (call-interactively cmd)))
 
     (let ((coding-system-for-read coding-system)
           (coding-system-for-write coding-system)
-          (coding-system-require-warning t)
-          (current-prefix-arg prefix))
+          (coding-system-require-warning t))
+      (setq current-prefix-arg prefix-arg prefix-arg nil)
+      ;; Have to bind `last-command-event' e.g. for `self-insert-command'.
+      (setq last-command-event (aref keyseq 0))
       (message "")
       (call-interactively cmd))))