bug#19875: 25.0.50; Setting an input-method-function breaks prefix show on the echo area

bug#19875: 25.0.50; Setting an input-method-function breaks prefix show on the echo area

[Óscar Fuentes]

emacs -Q
M-x set-input-method ENTER spanish-prefix ENTER

Now let's suppose that we want to execute a command with a numeric
prefix (say 42). Let's press C-u and wait until it is displayed on the
echo area, then press `4' and wait, then press `2' and wait until it
is displayed too. The echo area shows:

C-u C-u 4 C-u 4 2

The problem is not limited to `set-input-method'. I discovered it with
key-chord-mode. I also have echo-keystrokes set to a low value, which
makes the problem more jarring.



In GNU Emacs 25.0.50.5 (x86_64-unknown-linux-gnu, X toolkit)
 of 2015-01-03 on qcore
Repository revision: 11ee7d8bf16b8ee4fcb3659e4b09686ed8b10590
Windowing system distributor `The X.Org Foundation', version 11.0.11600000
System Description:	Ubuntu 14.10

Configured using:
 `configure --without-toolkit-scroll-bars --with-x-toolkit=lucid'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG SOUND GSETTINGS NOTIFY LIBXML2 FREETYPE XFT
ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

bug#19875: 25.0.50; Setting an input-method-function breaks prefix show on the echo area

[Eli Zaretskii]

> From: oscarfv@telefonica.net (Óscar Fuentes)
> Date: Sun, 15 Feb 2015 18:04:16 +0100
> 
> 
> emacs -Q
> M-x set-input-method ENTER spanish-prefix ENTER
> 
> Now let's suppose that we want to execute a command with a numeric
> prefix (say 42). Let's press C-u and wait until it is displayed on the
> echo area, then press `4' and wait, then press `2' and wait until it
> is displayed too. The echo area shows:
> 
> C-u C-u 4 C-u 4 2

This happens on the release branch, and in Emacs 24.4 as well.

bug#19875: 25.0.50; Setting an input-method-function breaks prefix show on the echo area

[Óscar Fuentes]

Eli Zaretskii <eliz@gnu.org> writes:

> This happens on the release branch, and in Emacs 24.4 as well.

The relevant area of code in keyboard.c is very old. The bug probably
has more than 15 years.

Semi-blind fix attempt:

diff --git a/src/keyboard.c b/src/keyboard.c
index bcb51cf..8b65f0e 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -3095,7 +3095,15 @@ read_char (int commandflag, Lisp_Object map,
 
       cancel_echoing ();
       ok_to_echo_at_next_pause = saved_ok_to_echo;
-      kset_echo_string (current_kboard, saved_echo_string);
+      /* Do not restore the echo area string if the user is
+         introducing a prefix argument. Otherwise we end with
+         repetitions of the partially introduced prefix
+         argument. (bug#19875) */
+      Lisp_Object pa = intern ("prefix-arg");
+      if (NILP(pa))
+        {
+          kset_echo_string (current_kboard, saved_echo_string);
+        }
       current_kboard->echo_after_prompt = saved_echo_after_prompt;
       if (saved_immediate_echo)
 	echo_now ();

bug#19875: 25.0.50; Setting an input-method-function breaks prefix show on the echo area

[Óscar Fuentes]

Fixed on 81d89d88aef5de720e7fbeecbfb295d6eaf6fd37