Subject: bug#48129: 28.0.50; Per file-handle (stdin, stdout and stderr) process-connection-type variable

From: Thomas Hisch <[email-masked]>
Date: Sun, 2 May 2021 12:19:21 +0200

On 5/1/21 8:09 AM, Eli Zaretskii wrote:
>> From: Thomas Hisch <[email-masked]>
>> Date: Sat, 1 May 2021 01:10:10 +0200
>>
>>
>> I would like that the configuration options of the three file
>> handles (stdin, stdout and stderr), when a new process is created
>> in emacs, are improved.  What I'm specifically asking for is to
>> add support for individually specifying for each file-handle
>> whether it should be connected to a pty or not.  Currently the
>> value of the process-connection-type variable applies to all
>> three file handles at once, which leads to a problem with the
>> following use-case:
>>
>> Usually a program outputs ANSI escape sequences when its stdout
>> file-handle is connected to a pty. It is currently not possible to
>> communicate with a subprocess that is created by `start-file-process' by
>> writing to a pty (via stdin) and avoiding that this subprocess writes
>> ANSI escape sequences to stdout. This use-case is needed by magit, which
>> currently doesn't have support for displaying ANSI escape sequences but
>> it needs to communicate with it's started subprocesses via a PTY
>> (https://github.com/magit/magit/issues/3549).
>
> We have make-pipe-process; can't you solve your problem by connecting
> your process's stdout to such a pipe-process?  If not, why not?
>

Thx Eli for the fast reply! I had to study the docs of make-pipe-process
and make-process to understand what you mean. However, I'm not fully
sure if I fully get what you mean.

AFAICS the pipe process which is returned by make-pipe-process can be
passed to the :stderr keyword argument of make-process. Is that what you
head in mind?

According to the docs of make-process, process-connection-type is
ignored if :stderr is passed to make-process:

 >  This parameter and the value of ‘process-connection-type’ are
ignored if a non-‘nil’ value is specified for the ‘:stderr’ parameter;
in that case, the type will always be ‘pipe’.

What I want is that stdout and stderr are connected to a pipe but stdin
is connected to a pty.

Here is the new test script that I used

(let* (
       (stderr-buffer (get-buffer-create "*stderr*"))
       (stderr-proc (make-pipe-process :name "stderr"
                       :buffer stderr-buffer))
       (process-buf (get-buffer-create "*temp*")))
     (make-process
      :name "isatty"
      :buffer process-buf ;; it is not possible to pass the output of
make-pipe-process to :buffer
      :connection-type 'pty ;; unfortunately ignored if :stderr is used
      :stderr stderr-proc
      :command (list "/tmp/output-isatty.py")))

Best regards
Thomas
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