bug#29473: 25.3; 'background-mode is 'light on console with black background

[Noam Postavsky]

Tim Landscheidt <tim@tim-landscheidt.de> writes:

> With interspersed message calls, I could find out that kon-
> sole's response to the "Secondary Device Attributes (DA)"
> query in terminal-init-xterm ("\e[>0c") is "^[[>0;115;0c":
> 
> | [tim@passepartout ~/src/emacs]$ perl -we 'print "\e[>0c";'; sleep 1; echo
> | ^[[>0;115;0c
> | [tim@passepartout ~/src/emacs]$
> 
> This version number (115) falls short of the test
> "(>= version 242)" which would cause the background colour
> to be queried, and rightly so, because konsole does not re-
> spond to the query "\e]11;?\e\\":
>
> | [tim@passepartout ~/src/emacs]$ perl -we 'print "\e]11;?\e\\";'; sleep 1; 
> echo
>
> | [tim@passepartout ~/src/emacs]$

> (Sidenote: gnome-terminal reports back "^[[>1;4603;0c" and
> "^[]11;rgb:2323/2727/2929^[\" but the latter is never que-
> ried due to NUMBER1 being 1 and NUMBER2 being greater than
> 2000, so background-mode stills end up as 'light with gnome-
> terminal.)

Ah, interesting.  It seems the versions of gnome-terminal are rather
non-standard.  Which version of gnome-terminal is this, and does it
support the other xterm calls?

        ;; If version is 216 (the version when modifyOtherKeys was
        ;; introduced) or higher, initialize the
        ;; modifyOtherKeys support.
        (when (>= version 216)
          (xterm--init-modify-other-keys))
        ;; In version 203 support for accessing the X selection was
        ;; added.  Hterm reports itself as version 256 and supports it
        ;; as well.  gnome-terminal doesn't and is excluded by this
        ;; test.
        (when (>= version 203)
          ;; Most xterms seem to have it disabled by default, and if it's
          ;; disabled, C-y will incur a timeout, so we only use it if the user
          ;; explicitly requests it.
          ;;(xterm--init-activate-get-selection)
          (xterm--init-activate-set-selection))))))

> So then I tried to track down where background-mode's 'light
> is actually coming from, and it seems to originate in
> frame-set-background-mode's:
>
> |            (default-bg-mode
> |              (if (or (window-system frame)
> |                      (and tty-type
> |                           (string-match 
> "^\\(xterm\\|\\rxvt\\|dtterm\\|eterm\\)"
                                                         ^^ 
Hmm, those backslashes are a bug, I think.
> |                                         tty-type)))
> |                  'light
> |                'dark))
>
> with tty-type being "xterm-256color".

> My assumption now is that Emacs's detection mechanism cannot
> be "fixed" for konsole in Fedora 25 and I should manually
> set frame-background-mode to 'dark.

Yes, looks like there is no way for Emacs to detect it.

> But: In Fedora 26, konsole 17.04.1 (in contrast to Fedora
> 25's konsole 16.12.3) still returns "^[[>0;115;0c" as
> version number, /but/ "\^[]11;rgb:0000/0000/0000^G" for the
> background colour.

Thanks for tracking all these details down!

> So one possible improvement could be to query the background
> colour either unconditionally or also on "(= version 115)".
> This would increase the start-up time by (at most) two se-
> conds (xterm-query-timeout) for terminals that do not sup-
> port this query AFAIUI.

Hmm, I think 2 seconds is too much.  Is there no way to distinguish
between konsole versions?  Perhaps file a bug against konsole to ask
them to bump the reported version?