Subject: Re: bug#7782: 24.0.50; 24.0.50: set-scroll-bar-mode missing under non-GUI environments

From: Tim Cross <[email-masked]>
Date: Sun, 16 Jan 2011 10:31:32 +1100

On Tue, Jan 11, 2011 at 9:58 AM, Glenn Morris <[email-masked]> wrote:

> Tim Cross wrote:
>
> > According to the documentation for scroll-bar-mode, the way to
> > set/change scroll-bar settings from within elisp code is to use the
> > set-scroll-bar-mode function. However, this function is only defined
> > when run under graphic capable environments, such as X, but not in other
> > environments such as the Linux console.
> >
> > This means that if you don't want your elisp or .emacs to raise an
> > error, you also need to wrap calls to this function inside something
> > like (when display-graphic-p ...). This is not required for other
> > display related functions that depend on an environment requiring
> > support for graphics i.e. tool-bar-mode.
>
> It's not clear to me whether you mean --without-x builds or --with-x
> builds started with -nw (or both), but in either case:
>
> In a with-x build:
> emacs -Q -nw
>
> C-h f tool-bar-mode
>  tool-bar-mode is an interactive compiled Lisp function in `tool-bar.el'.
>
> C-h f set-scroll-bar-mode
>  set-scroll-bar-mode is a compiled Lisp function in `scroll-bar.el'.
>
> (tool-bar-mode 1)             ; no error
>
> (set-scroll-bar-mode 'left)   ; no error
>
>
> In a without-x build, neither tool-bar-mode nor set-scroll-bar-mode is
> defined.
>
> Thus, I see no inconsistency here and don't understand your request.
>

OK, I just tried to re-create the error I was getting and now it isn't
occurring. I have updated emacs since logging the report, but cannot see
anything obvious in the change log that would explain the difference, so not
sure. For the record, here is what I did originally and which does not
repeat the problem now.

1. Built emacs under X with the GTK libs (emacs from bzr 24.0.50).
2. Login under the Linux console and run emacs --debug-init

Originally, I got a backtrace with a void function error for
set-scroll-bar-mode. Fixed this by putting the call inside a when block
which tested for a window-syste of X. However, noticed that this was not an
issue with tool-bar-mode. I could place a direct top-level call to
tool-bar-mode in my .emacs without needing to wrap it in a test. This was
the original inconsistency I observed. i.e. tool-bar-mode was defined but
set-scroll-bar-mode was not when running an emacs built with X under a Linux
console (not an xterm or X console).

C-h f tool-bar-mode returns docs on that function as would be expected.
C-h f set-scroll-bar-mode fails saying the function is not defined.

After removing the when block from my .emacs and just having a top level
call to set-scrolll-bar-mode and restarting emacs just now, I no longer get
the error and backtrace. C-h f returns info on both functions.

I cannot see anything in the change log which would explain why it was not
working and now is, so I guess I must have screwed up somewhere. Sorry for
the noise.

The main reason for the report was I figured we should have consistency -
either *all* graphics display related functions are always defined i.e. as
tool-bar-mode appears to be or *all* of them are defined only for
environments where they maie sense, such as X, but above all, avoid
situations where some appear to be defined and some do not.
Personally, I think they should all be defined regardless of the
environment, even if in many environments, they are just function stubs that
don't actually do anything. This avoids having to remember to put such code
inside tests and to somehow know which such functions are defined in which
environments. For the envrionments I've tested, this does not appear to be
the case for tool-bar-mode and set-scroll-bar-mode, so all appears to be
fine for at least these two cases.

thanks,

Tim