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

[Handa Kenichi <handa@gnu.org>]

In article <70ppui8gr4.fsf@fencepost.gnu.org>, Glenn Morris
<rgm@gnu.org> writes:

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

Ok.  Please wait for a while.

---
Kenichi Handa
handa@gnu.org

> 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 */