Re: Emacs-diffs Digest, Vol 2, Issue 28

[Kenichi Handa <handa@m17n.org>]

In article <E18b2yf-0007yS-00@fencepost.gnu.org>, Richard Stallman <rms@gnu.org> writes:
>     [...]
> 	    * process.c (read_process_output): Decide the multibyteness of
> 	    string given to a process filter by a coding system used for
> 	    decoding the process output.

>     But, I don't remeber the detail now.

> set-process-multibyte should be a good solution.

I think we have extrapolated the behaviour of process I/O
from that of file I/O.  But set-process-multibyte breaks it.
It's something like declaring the multibyteness of a process
but we don't declare that of a file.  So it's not easy to
extrapolate the exact semantics of set-process-multibyte.

It is fairly clear for the case that a process has a fileter
and coding system is no-conversion or raw-text.  But what to
do with the other coding systems (e.g. Latin-1,
iso-2022-jp).  If a process is unibyte, what kind of string,
the filter should get?  Should we suppress a text decoding
like the case of inserting a file into a unibyte buffer?

And if the process has no filter but has a buffer, what to
do for a unibyte process that has a multibyte buffer, or for
a multibyte process that has a unibyte buffer?

And what to do with process-send-string/region.

I think it is better to keep extrapolating the behaviour of
process reading/sending from file reading/writing.

For inserting a proecss output in a buffer, there's no
difficulty to extrapolate the behaviour.

For a filter, although we don't have a function something
like string-from-file, the most resembling code will be
this.

(with-temp-buffer
  (insert-file-contents FILE)
  (buffer-string))

A string given to a process filter must be the same as the
result of that code, which means that
default-enable-multibyte-characters decides the
multibyteness, and if it is nil, character conversion except
for end-of-line conversion is suppressed.

The only question is when to check
default-enable-multibyte-characters.  When a process is
created, or just before calling a filter?  I think the
former is more like file I/O.  And it may be ok to have a
function set-process-filter-multibyte which can change the
multibyteness of a string to a filter on the way.

Or, was the intention of set-process-multibyte actually
set-process-filter-multibyte?

---
Ken'ichi HANDA
handa@m17n.org