Re: [PATCH 0/1] Proper 24-bit TTY detection for Emacs 26.

[Rami Ylimäki]

> It's too late to make incompatible changes on the emacs-26 branch.
>
> I actually don't understand the motivation for the change.  Did the
> method we use now stop working in the recent versions of terminfo, and
> the "RGB" and "setaf"/"setab" replace "setf24"/"setb24" we use in the
> current code?  Or are the new attributes supported in addition to the
> old ones?  If the latter, why do we need to change anything?  And if
> the former, I think we want to support both, not just the new
> replacements.
The "set[bf]24" capabilities are only supported by Emacs, because 
traditionally Terminfo hasn't offered any way to detect direct color 
support. This workaround forces users to compile their own TERMs with 
these capabilities.

Latest Terminfo provides several TERMs with "-direct" suffix, such as 
"xterm-direct", that support "RGB" with "seta[bf]". We definitely want 
to support this.

I can open a bug about this and post a patch that supports both methods 
on Emacs 27, since it's too late for 26.

There might be some problems with Emacs 26 and TERM=xterm-direct, but I 
haven't properly investigated this yet. At least I already noticed some 
error messages from xterm.el:xterm-register-default-colors.