Only some ligatures are being applied

[wezm]

Check for existing issues

• Completed

Possibly related to #11127 but that is specifically about the terminal.

Describe the bug / provide steps to reproduce it

I have enabled ligatures in my settings.json:

  "buffer_font_family": "PragmataPro Mono Liga",
  "buffer_font_features": {
    "calt": true
  },

However only some of the expected ligatures are being applied. For example if I type <!-- it ligates correctly, as does => but != should ligate to ≠ and -> to something like → but they do not.

These are documented in the font handbook as part of calt as well as shown in other editors.

Environment

Zed: v1.0.0 (Zed Dev 71a94c7)
OS: Linux 1.0.0 (X11)
Memory: 62.5 GiB
Architecture: x86_64

If applicable, add mockups / screenshots to help explain present your vision of the feature

These screenshots show the difference in rendering between Zed and JetBrains Rust Rover both using the same font with ligatures enabled.

Zed:

In this one => is ligating but ->, >> in read::<CmapSubtable<'_>>() and // are not.

Rust Rover:

Zed:

In this one it appears that [[ and ]] are ligating but != is not.

Rust Rover:

If applicable, attach your ~/Library/Logs/Zed/Zed.log file to this issue.

No response

[JunkuiZhang]

Linux implementation dose not support font features for now.

[wezm]

Linux implementation dose not support font features for now.

Ahh I see, well I guess this can act as a tracking issue for the implementation. Here's the TODO:

zed/crates/gpui/src/platform/cosmic_text/text_system.rs

Lines 198 to 204 in 3ec9469

	// todo(linux) handle `FontFeatures`
	#[profiling::function]
	fn load_family(
	&mut self,
	name: &str,
	_features: &FontFeatures,
	) -> Result<SmallVec<[FontId; 4]>> {

[peppidesu]

Seems like we need to wait for pop-os/cosmic-text#229 to be resolved

[veryshyjelly]

Same thing happening in windows

[JunkuiZhang]

Same thing happening in windows

It's a bug introduced by #13854 , and the changes have been reverted via #14045 .

[flyInRust]

Same thing happening in ubuntu 24.04 zed 0.143.6

[flyInRust]

Same thing happening in ubuntu 24.04 zed 0.143.6

[t9t]

I'm facing this issue as well on Arch Linux using Zed 0.144.3.

@JunkuiZhang and @peppidesu could you explain in short how you came to the conclusion that this is about missing font feature support?

I am asking because some ligatures work fine, while others do not. E.g. as @wezm noted (and as you can see in his screenshot), => works while != does not. Some more examples of working ligatures are ==, :=, <=, and >=. Not working are e.g. ->, -->.

calt is a default font feature, and if I understand https:/zed-industries/zed-fonts/blob/main/params/ligation-set.toml correctly, it should include the not-working != by default (through exeq; i.e. not dependent on font features). Though I may be misunderstanding how default font features work.

[JunkuiZhang]

@t9t I implemented font feature support on Windows and macOS. However, it is currently impossible to implement font features on Linux because it uses the cosmic text system, which does not support setting font features. See pop-os/cosmic-text#229

[JunkuiZhang]

Linux uses CosmicTextSystem:

zed/crates/gpui/src/platform/linux/platform.rs

Line 107 in 7d30175

let text_system = Arc::new(CosmicTextSystem::new());

You can see that FontFeatures is not used:

zed/crates/gpui/src/platform/cosmic_text/text_system.rs

Lines 202 to 208 in 7d30175

	// todo(linux) handle `FontFeatures`
	#[profiling::function]
	fn load_family(
	&mut self,
	name: &str,
	_features: &FontFeatures,
	) -> Result<SmallVec<[FontId; 4]>> {

[t9t]

Thanks a lot. Let me rephrase my question. I would like to understand how the lack of implementation of font features lead to some ligatures missing, while other ligatures work.

[JunkuiZhang]

I guess this is some kind of default behavior that cosmic text provides?

Sorry I know little about cosmic text.

[andre0xFF]

Also not seeing ligatures on Ubuntu 22.04.4 LTS zed 0.144.4

[ruskiiamov]

same issue
ubuntu 22.04.4
zed 0.147.2
font Fira Code