Cherry-picked Iosevka ligatures work in other terminals, but not Ghostty

[ferdinandrau]

The popular Iosevka font allows users to create a custom build to fine-tune the appearance. I used this to selectively enable only some of the ligatures it offers, as I only want "non intrusive" ligations (like connected arrows -->) and not those that obscure the individual characters (like the connected != that turns into a strikethrough-equals ≠). My custom build works fine in Kitty and iTerm, but running Ghostty, all ligatures the font offers show up, even the ones I disabled:

The image has Ghostty on the left and iTerm, behaving as expected, on the right.

I am aware that this may not be a Ghossty issue, since this project is pretty good with standards, and perhaps Iosevka is not following one of them. But the other terminals handle the custom-built font just fine and display what is expected. I sadly don't know much about fonts and thus can't really judge where to report this issue.

Ghostty version (running on macOS 15.2):

Ghostty 1.0.1

Version
  - version: 1.0.1
  - channel: stable
Build Config
  - Zig version: 0.13.0
  - build mode : builtin.OptimizeMode.ReleaseFast
  - app runtime: apprt.Runtime.none
  - font engine: font.main.Backend.coretext
  - renderer   : renderer.Metal
  - libxev     : main.Backend.kqueue

How to reproduce:

1. This is the private-build-plans.toml used to build the font:

   [buildPlans.Ioveska]
   family = "Ioveska"
   serifs = "sans"
   spacing = "term"
   exportGlyphNames = true
   noCvSs = true
   
   [buildPlans.Ioveska.widths.Normal]
   shape = 560
   menu = 5
   css = "normal"
   
   [buildPlans.Ioveska.weights.Regular]
   shape = 450
   menu = 400
   css = 400
   
   [buildPlans.Ioveska.weights.Bold]
   shape = 750
   menu = 700
   css = 700
   
   [buildPlans.Ioveska.variants.design]
   asterisk = "penta-low"
   percent = "rings-continuous-slash"
   lig-single-arrow-bar = "with-notch"
   lig-double-arrow-bar = "with-notch"
   
   [buildPlans.Ioveska.ligations]
   enables = [
     "arrow-l",
     "arrow-r",
     "arrow-lr",
     "lteq-separate",
     "gteq-separate",
     "kern-dotty",
     "kern-bars",
   ]

   I could probably distribute the finished files (it's 4 .ttfs) under the license if desired. https://fontdrop.info shows that all ligatures, even the disabled ones, are still present in the file (duh).

2. Install the font and set it as the default:

   # ~/.config/ghostty/config
   
   font-family = Ioveska
   font-size = 15

   For comparison, also configure another Terminal like iTerm to use "Ioveska".

3. Enter something like >=. In Ghostty, it becomes a connected symbol, whereas iTerm and Kitty show the individual characters.

[tombell]

I was having the same issue over the last day, since I wanted to disable the /* and */ ligatures because they made globs in the terminal look bad. So I made a custom Iosevka with the slash-asterisk ligation removed.

I noticed whatever I did to build the font, it would still show /* and */ ligatures, however I also tried iTerm to double check, but with ligatures enabled in that, it still rendered the /* and */ ligatures.

I then started playing around with font-feature settings in Ghostty, and found that if I did font-feature = -dlig it would keep the other ligatures, but disable the ones I had disabled in the Iosevka build plan. So my custom Iosevka is "working" enough for me.

So not entirely sure if I don't fully unstand how Iosevka build plans work or if it's an "issue" with Ghostty.

Just thought I'd share some things I discovered while trying to figure this out myself.

[ferdinandrau]

Thanks, I just disabled dlig (and left calt on) and now i only get the ligatures i specified! Like you I have no idea if this is a Iosevka or Ghostty issue... but at least something works now. Was not able to reproduce the iTerm behavior you mentioned, though, every other terminal handles my custom-built font fine by default.