Add facility to collect stderr of async subprocess

* src/w32.h (register_aux_fd): New function declaration.
* src/w32.c (register_aux_fd): New function.
* src/process.h (struct Lisp_Process): New member stderrproc.
* src/process.c (PIPECONN_P): New macro.
(PIPECONN1_P): New macro.
(Fdelete_process, Fprocess_status, Fset_process_buffer)
(Fset_process_filter, Fset_process_sentinel, Fstop_process)
(Fcontinue_process): Handle pipe process specially.
(create_process): Respect p->stderrproc.
(Fmake_pipe_process): New function.
(Fmake_process): Add new keyword argument :stderr.
(wait_reading_process_output): Specially handle a pipe process when
it gets an EOF.
(syms_of_process): Register Qpipe and Smake_pipe_process.

* doc/lispref/processes.texi (Asynchronous Processes): Document
`make-pipe-process' and `:stderr' keyword of `make-process'.

* lisp/subr.el (start-process): Suggest to use `make-process' handle
standard error separately.

* test/automated/process-tests.el (process-test-stderr-buffer)
(process-test-stderr-filter): New tests.

* etc/NEWS: Mention new process type `pipe' and its usage with the
`:stderr' keyword of `make-process'.

1 files changed, 20 insertions, 0 deletions

diff --git a/src/w32.c b/src/w32.c
index 6f16704909c..8721ed919fc 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -9473,6 +9473,26 @@ serial_configure (struct Lisp_Process *p, Lisp_Object contact)
   pset_childp (p, childp2);
 }
 
+/* For make-pipe-process */
+void
+register_aux_fd (int infd)
+{
+  child_process *cp;
+
+  cp = new_child ();
+  if (!cp)
+    error ("Could not create child process");
+  cp->fd = infd;
+  cp->status = STATUS_READ_ACKNOWLEDGED;
+
+  if (fd_info[ infd ].cp != NULL)
+    {
+      error ("fd_info[fd = %d] is already in use", infd);
+    }
+  fd_info[ infd ].cp = cp;
+  fd_info[ infd ].hnd = (HANDLE) _get_osfhandle (infd);
+}
+
 #ifdef HAVE_GNUTLS
 
 ssize_t