bug#62265: Underline does not work in Terminal Emacs

[Eli Zaretskii <eliz@gnu.org>]

> From: Mohsin Kaleem <mohkale@kisara.moe>
> Cc: jporterbugs@gmail.com, 62265@debbugs.gnu.org
> Date: Sun, 19 Mar 2023 11:51:45 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > However, what about the non-TERMINFO branch?  Do termcap databases
> > support this capability and tigetstr?  I wonder whether we should do
> > one of the following:
> >
> >   . support "smxx" only when TERMINFO is defined
> >   . support "smxx" regardless of whether TERMINFO is defined
> 
> The latter wouldn't be possible for those using terminfo because of the
> issue I described before. I'm okay with the former approach but I
> imagine the author of the original TTY strikethrough patch was building
> Emacs without terminfo and they described the patch as working for them
> so I'd have to conclude termcap does support this (in a non-compliant
> ncurses way). Switching to the former approach might break their
> workflow since if they build without terminfo they'd lose strikethrough
> altogether. I'm happy to test whether this would be the case but not
> sure how to. The difference between termcap and terminfo seem kinda
> arbitrary to me and I can't find any documentation describing the exact
> difference (except this sort of 2 letter restriction in termcap
> extensions).

If your hypothesis is correct, I'm fine with leaving the non-TERMINFO
branch using tgetstr.  But is it indeed correct?

Let's ask the author of that strikethrough patch.  Mike, can you tell
whether you tested the patch on a system with or without terminfo?
And what, if anything, can you tell about using tgetstr for
capabilities whose names are more than 2 characters -- is that
supported with the curses library you were using at the time?

Thanks.