TTY frames parameters

TTY frames parameters

[Eli Zaretskii]

There's a strange subtle difference between the first tty frame
created on a default terminal and all the other frames: the first one
has its `tty' association with nil cdr, while the rest have
"/dev/tty".  Is that a bug?

To reproduce:

  emacs -Q -nw
  M-: (frame-parameter (selected-frame) 'tty) RET => nil
  C-x 5 b foo
  M-: (frame-parameter (selected-frame) 'tty) RET => "/dev/tty"

You will also see that in the initial frame, (frame-parameters)
returns an alist that contains `(tty)', not `(tty . "/dev/tty")' as in
the other frames.

Re: TTY frames parameters

[Alan Mackenzie]

Hi, Eli,

On Sun, Aug 24, 2008 at 11:39:37PM +0300, Eli Zaretskii wrote:
> There's a strange subtle difference between the first tty frame
> created on a default terminal and all the other frames: the first one
> has its `tty' association with nil cdr, while the rest have
> "/dev/tty".  Is that a bug?

What does the frame parameter tty mean?  I couldn't find it described in
the Elisp manual.  Surely _that_ is a bug.

> To reproduce:

>   emacs -Q -nw
>   M-: (frame-parameter (selected-frame) 'tty) RET => nil
>   C-x 5 b foo
>   M-: (frame-parameter (selected-frame) 'tty) RET => "/dev/tty"

On Emacs 22, there doesn't seem to be a frame-parameter called tty.  On
Emacs 23, (running as emacs -Q on a Linux tty), I get the same symptoms
as you do.

> You will also see that in the initial frame, (frame-parameters)
> returns an alist that contains `(tty)', not `(tty . "/dev/tty")' as in
> the other frames.

-- 
Alan Mackenzie (Nuremberg, Germany).

Re: TTY frames parameters

[Eli Zaretskii]

> Date: Sun, 24 Aug 2008 21:54:35 +0000
> Cc: emacs-devel@gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> On Sun, Aug 24, 2008 at 11:39:37PM +0300, Eli Zaretskii wrote:
> > There's a strange subtle difference between the first tty frame
> > created on a default terminal and all the other frames: the first one
> > has its `tty' association with nil cdr, while the rest have
> > "/dev/tty".  Is that a bug?
> 
> What does the frame parameter tty mean?

It's a device on which the terminal frame is displayed.  More
specifically, the calls to fwrite Emacs does to write glyphs as part
of the frame's display go to a FILE stream open on this device.

> I couldn't find it described in the Elisp manual.  Surely _that_ is
> a bug.

This parameter was introduced by the mult-tty feature.  None of that
is documented yet, except very minimally in etc/NEWS.

> On Emacs 22, there doesn't seem to be a frame-parameter called tty.  On
> Emacs 23, (running as emacs -Q on a Linux tty), I get the same symptoms
> as you do.

Thanks for testing.  I hope someone will be able to answer my
question.

Re: TTY frames parameters

[Eli Zaretskii]

> Date: Sun, 24 Aug 2008 23:39:37 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> There's a strange subtle difference between the first tty frame
> created on a default terminal and all the other frames: the first one
> has its `tty' association with nil cdr, while the rest have
> "/dev/tty".  Is that a bug?
> 
> To reproduce:
> 
>   emacs -Q -nw
>   M-: (frame-parameter (selected-frame) 'tty) RET => nil
>   C-x 5 b foo
>   M-: (frame-parameter (selected-frame) 'tty) RET => "/dev/tty"
> 
> You will also see that in the initial frame, (frame-parameters)
> returns an alist that contains `(tty)', not `(tty . "/dev/tty")' as in
> the other frames.

Since no one responded, I made a change in dispnew.c to have a non-nil
cdr in `tty's association on the initial frame as well.  Please holler
if I did something wrong.

Re: TTY frames parameters

[Stefan Monnier]

> Since no one responded, I made a change in dispnew.c to have a non-nil
> cdr in `tty's association on the initial frame as well.  Please holler
> if I did something wrong.

Thanks,


        Stefan