Re: x-migrant.el - handle subprocesses over multiple X displays

[Stefan Monnier <address@hidden>]

> ;; This package advises the Emacs process startup functions, so that
> ;; they set up the DISPLAY environment variable correctly.  This is
> ;; very useful if you run the same Emacs session on multiple X
> ;; displays at once, and sometimes need to pop up an X application
> ;; from within Emacs.

Sounds cool.  Maybe this should be integrated directly in the C code.

> (defmacro current-x-display-name ()
>   "Return the name of the currently active X display, or nil for none."
>   (if xm-running-xemacs
>       '(if (eq (frame-type) 'x)
>         (device-connection))
>     '(frame-parameter nil 'display)))

Testing for `xemacs' is generally bad style.  How about:

   (if (fboundp 'device-connection)
       (defun current-x-display-name ()
         (if (eq (frame-type) 'x)
          (device-connection)))
     (defun current-x-display-name ()
       (frame-parameter nil 'display)))

or

   (defun current-x-display-name ()
     "Return the name of the currently active X display, or nil for none."
     (if (fboundp 'device-connection)
         (if (eq (frame-type) 'x)
           (device-connection))
       (frame-parameter nil 'display)))

> (defmacro with-current-x-display (&rest body)
>   "Evaluate BODY with the DISPLAY environment variable set correctly.
> In this case, we take 'correct' as being the display on which the
> frame that currently has the focus is showing."
>   (let ((dpy (gensym "dpy-")))

Better use `make-symbol' which is more efficient and doesn't require CL.

>           (process-environment
>            (if ,dpy
>                (mapcar (function (lambda (env)
>                                    (if (string-match "^DISPLAY=" env)
>                                        (concat "DISPLAY=" ,dpy)
>                                      env)))
>                        process-environment)
>              process-environment)))

You don't need to replace DISPLAY, you can simply add another one and it
will shadow any potential older one:

            (process-environment
             (if ,dpy
                 (cons (concat "DISPLAY=" ,dpy) process-environment)
               process-environment)))

> (if xm-running-xemacs

Better test for (fboundp 'start-process-internal)
and (fboundp 'call-process-internal).


        Stefan