Background mode (was: Diff mode faces)

[Juri Linkov]

>> I see there is a bug not caused by my patch:
>> 
>>   emacs -q -nw -rv
>> 
>> sets the background mode to light on xterm.  But since -rv switches
>> foreground and background, it should switch the background mode too
>> from light to dark on xterm.
>
> I think this is a bug.

There are also other ways to reproduce this bug, for example, running
Emacs without -rv option on xterm and evaluating (invert-face 'default).
Every time it evaluated, it switches the background mode to a
reversed value: with real black background it sets the light
background mode; with white background - to dark mode.  That's because
xterm presence is checked only once in startup.el (with setting the
mode to light), but any subsequent call of `frame-set-background-mode'
ignores the fact that Emacs runs on xterm.  On rxvt (invert-face 'default)
doesn't change the background mode at all because rxvt.el sets the
value of `frame-background-mode' permanently.

-- 
Juri Linkov
http://www.jurta.org/emacs/