support undercurls for TERM=kitty (and TERM=xterm-kitty)

[gerion0]

• nvim --version: 0.4.3
• vim -u DEFAULTS (version: ) behaves differently? unknown, not relevant
• Operating system/version: Gentoo Linux
• Terminal name/version: Kitty 0.16.0
• $TERM: This is the source of the problem: "kitty" or "xterm-kitty"

Actual behaviour

When using Kitty as terminal, it has the extra feature of curly underlines. This is supported in neovim (#7479, #9052).

For terminal, it is benefitial that their terminfo files are in the ncurses database. This is the case for kitty, too. Ncurses includes kitty since quite a time but not as "xterm-kitty" but only as "kitty" (kitty bug, ncurses file). I have ncurses 6.1 from 2019.06.09 (gentoo package), that includes this file.

When I now switch from "xterm-kitty" the "kitty" as TERM variable the undercurls are gone, but replaced by underlines.

Expected behaviour

The undercurls are shown, regardless whether TERM is "kitty" or "xterm-kitty".

Addtional info

I tried to patch neovim:

diff --git a/src/nvim/tui/tui.c b/src/nvim/tui/tui.c
index 22f4501be..5440d743a 100644
--- a/src/nvim/tui/tui.c
+++ b/src/nvim/tui/tui.c
@@ -1523,7 +1523,8 @@ static void patch_terminfo_bugs(TUIData *data, const char *term,
   bool xterm = terminfo_is_term_family(term, "xterm")
     // Treat Terminal.app as generic xterm-like, for now.
     || nsterm;
-  bool kitty = terminfo_is_term_family(term, "xterm-kitty");
+  bool kitty = terminfo_is_term_family(term, "xterm-kitty")
+     || terminfo_is_term_family(term, "kitty");
   bool linuxvt = terminfo_is_term_family(term, "linux");
   bool bsdvt = terminfo_is_bsd_console(term);
   bool rxvt = terminfo_is_term_family(term, "rxvt");

However, this does not seem to affect the undercurl problem.

[teto]

I can confirm it's package under the kitty name with ncurses 6.1-20190112 too. Feel free to open up a PR, I will try locally.

[gerion0]

package? Do you mean fail?

I don't have a patch. The above mentioned patch does not work (this was also a wild guess, I grepped the source for "kitty", I don't know anything about the code base).

[blueyed]

Haven't investigated, but JFI: kitty itself $TERMINFO when installing it manually, and Arch Linux ships xterm-kitty in the kitty-terminfo package.

[blueyed]

@gerion0 check

neovim/src/nvim/tui/tui.c

Line 1943 in 78ec95c

int ext_bool_Su = unibi_find_ext_bool(ut, "Su"); // used by kitty

I.e. see if TERM=kitty infocmp -x contains Su - IIRC this is something that ncurses would not add, since it is a custom kitty extension.

[blueyed]

..it likely boils down to "kitty" in ncurses being different from "xterm-kitty" from Kitty itself?
(you can use infocmp to compare them, and/or diff the output from infocmp -x)

[gerion0]

..it likely boils down to "kitty" in ncurses being different from "xterm-kitty" from Kitty itself?

Yes, exactly that. The Su extension is not reported with TERM=kitty. Ok, so this is not a neovim but a ncurses problem.

Haven't investigated, but JFI: kitty itself $TERMINFO when installing it manually, and Arch Linux ships xterm-kitty in the kitty-terminfo package.

Yes, that is also mentioned in the kitty bug (see first post). In short: Kitty provides its own terminfo package and recommends it. However, on machines that you ssh into from a kitty terminal that don't have this extra terminfo package installed your terminal is broken. Therefore a (correct) entry in the ncurses database would be better.