Add file name handler support for 'make-process' (Bug#28691)

* src/process.c (Fmake_process): Add new keyword argument
':file-handler'.
(syms_of_process) <make-process, :file-handler>: Define new symbols.

* lisp/files.el (file-name-non-special): Add support for
'make-process'.

* test/src/process-tests.el (make-process/file-handler/found)
(make-process/file-handler/not-found)
(make-process/file-handler/disable): New unit tests.
(process-tests--file-handler): New helper function.

* test/lisp/files-tests.el
(files-tests-file-name-non-special-make-process): New unit test.

* doc/lispref/files.texi (Magic File Names): Document that
'make-process' can invoke file name handlers.

* doc/lispref/processes.texi (Asynchronous Processes): Document
':file-handlers' argument to 'make-process'.

* etc/NEWS (Lisp Changes in Emacs 27.1): Mention new
:file-handler argument for 'make-process'.

2 files changed, 10 insertions, 2 deletions

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 5b428b6205d..d929978b6ea 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -3171,6 +3171,7 @@ first, before handlers for jobs such as remote file access.
 @code{make-directory},
 @code{make-directory-internal},
 @code{make-nearby-temp-file},
+@code{make-process},
 @code{make-symbolic-link},@*
 @code{process-file},
 @code{rename-file}, @code{set-file-acl}, @code{set-file-modes},
@@ -3227,6 +3228,7 @@ first, before handlers for jobs such as remote file access.
 @code{make-auto-save-file-name},
 @code{make-direc@discretionary{}{}{}tory},
 @code{make-direc@discretionary{}{}{}tory-internal},
+@code{make-process},
 @code{make-symbolic-link},
 @code{process-file},
 @code{rename-file}, @code{set-file-acl}, @code{set-file-modes},
diff --git a/doc/lispref/processes.texi b/doc/lispref/processes.texi
index 402691c6bcf..d72f5b880a2 100644
--- a/doc/lispref/processes.texi
+++ b/doc/lispref/processes.texi
@@ -696,6 +696,12 @@ non-@code{nil} value should be either a buffer or a pipe process
 created with @code{make-pipe-process}, described below.  If
 @var{stderr} is @code{nil}, standard error is mixed with standard
 output, and both are sent to @var{buffer} or @var{filter}.
+
+@item :file-handler @var{file-handler}
+If @var{file-handler} is non-@code{nil}, then look for a file name
+handler for the current buffer's @code{default-directory}, and invoke
+that file handler to make the process.  If there is no such handler,
+proceed as if @var{file-handler} were @code{nil}.
 @end table
 
 The original argument list, modified with the actual connection
@@ -704,8 +710,8 @@ information, is available via the @code{process-contact} function.
 The current working directory of the subprocess is set to the current
 buffer's value of @code{default-directory} if that is local (as
 determined by `unhandled-file-name-directory'), or "~" otherwise.  If
-you want to run a process in a remote directory use
-@code{start-file-process}.
+you want to run a process in a remote directory, pass
+@code{:file-handler t} to @code{make-process}.
 @end defun
 
 @defun make-pipe-process &rest args