Re: When is an xterm's t_Co detected?

On 2015-12-31, Bram Moolenaar wrote:
> Gary Johnson wrote:
>
> > I recently learned that Vim can query an xterm directly for the
> > number of colors it supports. (This is not necessarily the same
> > value reported by terminfo. Otherwise, it wouldn't be very useful.)
> > Vim then sets t_Co to this number. I would like to use that value
> > to affect other color settings, but I can't figure out when to do
> > that. I captured the value of &t_Co at the start and end of my
> > ~/.vimrc and upon these autocommand events,
> >
> > BufWinEnter
> > ColorScheme
> > FileType
> > OptionSet
> > TermResponse
> > VimEnter
> >
> > but the value was always 8. By the time I queried the value from
> > Vim's command line, though, the value was 256.
> >
> > What event do I need to wait for to determine that t_Co may have
> > changed to 256?
>
> Can't think of something. We do have the OptionSet autocommand event,
> but it's not triggered in this case. Perhaps we should make a change
> for that. The code is near the end of set_num_option().

That seems like the right thing to do. I'm trying to think of what
could go wrong. I'm concerned about this statement under ":help
OptionsSet":

Note: It's a bad idea to reset an option
during this autocommand, this may break a
plugin. You can always use `:noa` to prevent
triggering this autocommand.

I was considering having this autocommand execute a :colorscheme
{name} command. That would often set 'background'. And if "nested"
was used, it would trigger a ColorScheme event.

That all seems OK. I'll look at creating a patch.

Regards,
Gary

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