Comparing against the old value before setting matched the original
C implementation, but there is no reason to use this restriction. In
particular, this inhibits using OptionSet to determine when the option
was set. If users need to handle a case where the option _changed_, it
is easy to do so in an OptionSet autocommand using v:option_new and
v:option_old (and friends).
Enable 'termguicolors' automatically when Nvim can detect that truecolor
is supported by the host terminal.
If $COLORTERM is set to "truecolor" or "24bit", or the terminal's
terminfo entry contains capabilities for Tc, RGB, or setrgbf and
setrgbb, then we assume that the terminal supports truecolor. Otherwise,
the terminal is queried (using both XTGETTCAP and SGR + DECRQSS). If the
terminal's response to these queries (if any) indicates that it supports
truecolor, then 'termguicolors' is enabled.
The OptionSet autocommand does not fire until Vim has finished starting,
so setting 'background' before the VimEnter event would not fire the
OptionSet event. The prior implementation also waited until VimEnter to
set 'background', so this was a regression introduced when moving
background detection into Lua.
This fixes an error that can occur in certain pathological cases when
the autocommand fires at just the right time such that it attempts to
close the timer after the timer has already exited, but before the
scheduled callback has fired.
We now let the timer continue to run even when the autocommand deletes
itself to avoid having to repeat the cleanup code multiple times. There
is no harm in letting the timer execute if the autocommand does not
exist, as the pcall will catch the error.
