ncurses terminfo has some issues

[jclulow]

There are a couple of issues with the terminfo.src in the current ncurses source.

First, the unfortunate reality is that lots of people use xterm and xterm-256color for terminals other than a strictly compliant xterm. The current database appears to include a rep capability, but many terminals don't implement this correctly. The graphical corruption is pretty obvious if you use something like ncdu which will make use of the repeating functionality, in a terminal like urxvt.

Ditching the rep capability from the xterm definition causes ncurses to fall back to something slightly less efficient, but widely supported: drawing the character multiple times. This seems a low risk, high value patch we could carry.

Second, tmux encourages users to use TERM=screen or screen-256color. A change was made just prior to the 6.2 release, it seems, that causes the old screen definition to be ditched in favour of one that inherits the ecma+index base:

# 2019-06-30
...
#       + use ecma+index in screen, st -TD?

This definition includes a rin capability that flat out doesn't work with tmux:

# ECMA-48 does not include the VT100 indexing and scroll-margins.  It has its
# own variation.
ecma+index|ECMA-48 scroll up/down,
        indn=\E[%p1%dS, rin=\E[%p1%dT,

(i.e., CSI n T does nothing)

In a subsequent version, this was apparently corrected:

20190803
...
        + amend the change to screen, because tmux relies upon that entry
          and does not support that feature (Debian #933572) -TD

Unfortunately I think we only get a new terminfo.src when we get a new ncurses release. I think it'd be a good idea for pkgsrc to contain a wholesale copy of terminfo.src which can be somewhat detached form the ncurses update process. We could also carry local modifications on the file. This is, I believe, what most distributions end up having to do, to manage the churn which is at times unhelpful.

What do you think?

[jperkin]

Both issues fixed in NetBSD@4a21729 and NetBSD@e8a4d5a.

For now I'm going to hold off on maintaining our own copy of terminfo.src as it's not without risk (it's likely we'd maintain it as a patch against upstream pkgsrc which would be inherently vulnerable to bit-rot), but if we see regressions again then we'll strongly consider it.

A fixed ncurses-6.2nb2 package will be available in the next trunk build, as well as our 2020Q1 release.

[jclulow]

Thanks!