bug#28691: [PATCH] Add file name handler support for 'make-process' (Bug#28691)

[Michael Albinus <michael.albinus@gmx.de>]

Eli Zaretskii <eliz@gnu.org> writes:

Hi Eli,

>> What happens, if no file name handler is found? Should there be a local
>> process then, or should this be ignored (returning nil)?
>
> The proposed code runs the process locally, which I think is
> reasonable.

Yes, when default-directory is local.

If default-directory is remote, and :file-handler indicates that a
remote process shall run, the situation is different. If the
corresponding file name handler offers an own make-network-process
implementation, it returns that process. But if the file name handler
misses an implementation, no local process shall run.

This is the same situation as with start-file-process. The file name
handler for ssh returns a process object:

--8<---------------cut here---------------start------------->8---
(with-temp-buffer
  (let ((default-directory "/ssh::"))
    (start-file-process "foo" (current-buffer) "/bin/true")))
=> #<process foo>
--8<---------------cut here---------------end--------------->8---

But for Tramp methods which do not own a start-file-process
implementation, no process is created:

--8<---------------cut here---------------start------------->8---
(with-temp-buffer
  (let ((default-directory "/sftp::"))
    (start-file-process "foo" (current-buffer) "/bin/true")))
=> nil
--8<---------------cut here---------------end--------------->8---

This is documented in the Lisp Manual, see node "Asynchronous Processes":

--8<---------------cut here---------------start------------->8---
     Some file handlers may not support ‘start-file-process’ (for
     example the function ‘ange-ftp-hook-function’).  In such cases,
     this function does nothing and returns ‘nil’.
--8<---------------cut here---------------end--------------->8---

I believe make-network-process shall be have similar.

Best regards, Michael.