bug#8522: Arrow key trouble when keyboard encoding is euc-japan

[Glenn Morris]

Please could you take a look at this report?
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8522

IIJIMA Hiromitsu wrote:

> I am using Emacs 23.2.1 on FreeBSD and RedHat (32-bit versions).
>
> I have configured keyboard-encoding-system be "euc-japan" because
> it is the terminal's default.
>
> But when I upgraded Emacs to ver. 23, arrow keys began to cause
> troubles when I run Emacs inside a terminal window (emacs -nw).
>
> When I move cursor with an arrow key, the cursor movement is
> reflected to the screen with one stroke delay.
> C-l shows the cursor's "real" position.
> It does not happen when I move cursor by C-f, C-n, etc.
>
> HOW-TO-REPEAT: Open a file and type C-x RET k euc-japan RET.
>
> According to the following site (in Japanese),
> http://slashdot.jp/~doda/journal/516198
> the cause of this trouble is that arrow keys are passed to Emacs as
> ESC O {A,B,C,D} sequence and this "ESC O" is interpreted as ISO/IEC
> 2022's SS3 (single-shift 3) code.
>
> This trouble occurs when the following conditions are all met:
> - ISO/IEC 2022 compliant or their variants
> - Using SS3
> - A character set designated to G3 by default
>
> At this moment, only Japanese EUC and its variants match the conditions.
>
> There are some encodings that use single-shifts: iso-2022-jp-2,
> iso-2022-cn, and iso-2022-cn-ext. But
>
>   - iso-2022-jp-2 and iso-2022-cn use SS2 and do not use SS3,
>   and
>   - iso-2022-cn-ext uses SS3 but in this encoding G3 is empty
>     at the boot time.
>
> In addition, iso-2022-cn-ext is a 7-bit encoding and therefore you can
> assume that in a 8-bit encoding, namely only Japanese EUC and its
> variants, a SS3 is followed by GR byte sequence, and treat the sequence
> "SS3 + GL-byte" as a void character.
>
> The site above published the following patch.
> Would you consider applying it? Thanks in advance.
>
> --- src/coding.c.orig    2010-04-04 07:26:13.000000000 +0900
> +++ src/coding.c    2010-09-24 16:42:33.000000000 +0900
> @@ -3853,8 +3853,14 @@
>           else
>         charset = CHARSET_FROM_ID (charset_id_2);
>           ONE_MORE_BYTE (c1);
> -          if (c1 < 0x20 || (c1 >= 0x80 && c1 < 0xA0))
> -        goto invalid_code;
> +          if (CODING_ISO_FLAGS (coding) & CODING_ISO_FLAG_SEVEN_BITS) {
> +        if (c1 < 0x20 || c1 >= 0x80)
> +          goto invalid_code;
> +          }
> +          else {
> +        if (c1 < 0xA0)
> +          goto invalid_code;
> +          }
>           break;
>
>         case 'O':        /* invocation of single-shift-3 */
> @@ -3867,8 +3873,14 @@
>           else
>         charset = CHARSET_FROM_ID (charset_id_3);
>           ONE_MORE_BYTE (c1);
> -          if (c1 < 0x20 || (c1 >= 0x80 && c1 < 0xA0))
> -        goto invalid_code;
> +          if (CODING_ISO_FLAGS (coding) & CODING_ISO_FLAG_SEVEN_BITS) {
> +        if (c1 < 0x20 || c1 >= 0x80)
> +          goto invalid_code;
> +          }
> +          else {
> +        if (c1 < 0xA0)
> +          goto invalid_code;
> +          }
>           break;
>
>         case '0': case '2':    case '3': case '4': /* start composition */