bug#62237: 28.1 or higher: 24-bit true color breaks colours in Emacsen built without X under GNU Screen

[Robert Pluim]

>>>>> On Sat, 18 Mar 2023 10:34:10 +0000, Sebastian Tennant <sdt@sebyte.me> 
>>>>> said:

    Sebastian> Quoth Eli Zaretskii <eliz@gnu.org>
    Sebastian> on Sat, 18 Mar 2023 11:09:10 +0200:
    >>>>> […] machines you are able to do a rlogin and still keep the
    >>>>> correct termcap/terminfo entry.  The terminal name is put in the
    >>>>> $TERM variable of all new windows.  Screen also sets the $TERMCAP
    >>>>> variable reflecting the capabilities of the virtual terminal
    >>>>> emulated. Notice that, however, on machines using the terminfo
    >>>>> database this variable has no effect.  Furthermore, the variable
    >>>>> $WINDOW is set to the window number of each window.
    >>>>> 
    >>>> This seems to tell how 'screen' figures out the terminal name, not
    >>>> how it sets TERM.  I asked who and why sets TERM to
    >>>> screen.SOMETHING.
    >>>> 
    >>> screen does: "The terminal name is put in the $TERM variable of all
    >>> new windows."
    >>> 
    >> So how did Emacs ever succeed to work inside screen, then?  AFAIK,
    >> we never supported this form of TERM's value.

    Sebastian> If you discard the ‘screen.’ prefix by explicitly setting TERM 
in your
    Sebastian> .screenrc; for example:

    Sebastian>  term xterm-256color

    Sebastian> it makes no difference, i.e. colours are still broken (when 
COLORTERM
    Sebastian> is set to ‘truecolour’).

Hmm, I get 24-bit colour in that case. Presumably because screen +
gnome-terminal supports it.

Robert
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