window config override for harfbuzz_features doesn't work if font already specifies them

[LunarLambda]

What Operating System(s) are you seeing this problem on?

Linux X11

Which Wayland compositor or X11 Window manager(s) are you using?

GNOME

WezTerm version

wezterm 20240513-184050-44b61d7e

Did you try the latest nightly build to see if the issue is better (or worse!) than your current version?

Yes, and I updated the version box above to show the version of the nightly that I tried

Describe the bug

Following the advice of #5403 (comment), I tried to set a window config override for harfbuzz_features, however it does not take precedence over the harfbuzz features described in my config's font setting.

Also, the toggle-ligature example here doesn't work if the font specifies harfbuzz_features already.

The issue is that I have multiple fonts with different harfbuzz_features set:

    -- These both had 'calt=0' previously
    font = w.font_with_fallback {
        {
            family = 'Berkeley Mono',
        },
        {
            family = 'FiraCode Retina',
            harfbuzz_features = { 'ss03', 'ss05' }
        },
    },

And I would simply like to add/remove calt=0 from the list for all of them, and keep the remaining features as specified.

To Reproduce

No response

Configuration

My config:

local w = require 'wezterm'

w.on('update-status', function(window, pane)
    local wo = window:get_config_overrides() or {}

    if pane:is_alt_screen_active() then
        wo.harfbuzz_features = { 'calt=1' }
    else
        wo.harfbuzz_features = { 'calt=0' }
    end

    window:set_config_overrides(wo)
end)

return {
    font = w.font_with_fallback {
        {
            family = 'Berkeley Mono',
        },
        {
            family = 'FiraCode Retina',
            harfbuzz_features = { 'ss03', 'ss05' }
        },
    },
    font_size = 15,
    freetype_load_target = 'Light',
    freetype_render_target = 'HorizontalLcd',
}

Repro using the example from documentation:

local wezterm = require 'wezterm'

wezterm.on('toggle-ligature', function(window, pane)
  local overrides = window:get_config_overrides() or {}
  if not overrides.harfbuzz_features then
    -- If we haven't overridden it yet, then override with ligatures disabled
    overrides.harfbuzz_features = { 'calt=0', 'clig=0', 'liga=0' }
  else
    -- else we did already, and we should disable out override now
    overrides.harfbuzz_features = nil
  end
  window:set_config_overrides(overrides)
end)

return {
  keys = {
    {
      key = 'E',
      mods = 'CTRL',
      action = wezterm.action.EmitEvent 'toggle-ligature',
    },
   font = w.font { family = 'FiraCode Retina', harfbuzz_features = { 'ss03', 'ss05' } },
  },
}

When removing harfbuzz_features from font, it works. Else it does not.

Expected Behavior

window config override harfbuzz_features should be appended/merged with harfbuzz_features set by the current font.

I want to avoid duplicating my font configuration in multiple places, and manually adding/removing elements from the harfbuzz_features table for each font or determining which font is currently being used seems difficult given the APIs provided by wezterm.

Logs

14:01:27.304 INFO wezterm_gui > Spawned your command via the existing GUI instance. Use wezterm start --always-new-process if you do not want this behavior. Result=SpawnResponse { tab_id: 2, pane_id: 2, window_id: 2, size: TerminalSize { rows: 24, cols: 80, pixel_width: 640, pixel_height: 384, dpi: 0 } }

Anything else?

No response