bug#12972: [PATCH] Avoid regression in mailcap-view-file similar to Bug#44824

[Maxim Nikulin <manikulin@gmail.com>]

On 02/07/2021 01:38, Eli Zaretskii wrote:
>> From: Maxim Nikulin Date: Fri, 2 Jul 2021 00:01:59 +0700
>>
>> --- a/lisp/net/mailcap.el
>> +++ b/lisp/net/mailcap.el
>> -    (start-process-shell-command command nil command)))
...
>> +    (make-process
>> +     :name "mailcap-view-file" :connection-type 'pipe :noquery t
>> +     :buffer nil ; "*Messages*" may be suitable for debugging
>> +     :sentinel (lambda (proc event)
>> +                 (when (and (memq (process-status proc) '(exit signal))
>> +                            (/= (process-exit-status proc) 0))
>> +                   (message
>> +                    "Command %s: %s."
>> +                    (mapconcat #'identity (process-command proc) " ")
>> +                    (substring event 0 -1))))
>> +     :command (list shell-file-name shell-command-switch command))))
> 
> First, you replace start-process-shell-command with make-process, and
> I'm not sure I understand why.  If all you want is to use pipes, why
> not simply bind process-connection-type around the call to
> start-process-shell-command?

>> +    ;; An alternative is `process-connection-type' let-bound to nil for
>> +    ;; `start-process-shell-command' call (with no chance to report failure).
-----------------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

>> If main process of the handler fails then show a message with exit
>> reason.
---^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> And with other handlers, this could be an
> incompatible behavior change if the handler behaves differently when
> its standard handles are connected to a pipe rather than a terminal
> device.

Example of such handler, please.