[Bug] Certain CJK fonts on NixOS causing crash in getRequiredFeature

[dweymouth]

Some users of my Fyne app have reported a crash on NixOS when the app tries to render CJK characters. I have no idea what font it is looking up and I haven't reproduced it myself since I do not have a Nix system, so unfortunately I don't have too much useful info, but the stack trace is:

panic: runtime error: index out of range [0] with length 0

goroutine 170 [running]:
github.com/go-text/typesetting/harfbuzz.getRequiredFeature(...)
	github.com/go-text/[email protected]/harfbuzz/ot_layout.go:247
github.com/go-text/typesetting/harfbuzz.(*otMapBuilder).compile(0x468616e69?, 0xe2b820?, {0xffffffffffffffff, 0xffffffffffffffff})
	github.com/go-text/[email protected]/harfbuzz/ot_map.go:146 +0x12f5
github.com/go-text/typesetting/harfbuzz.(*otShapePlanner).compile(0xc0027bc000, 0xc0027b6710, {0xffffffffffffffff, 0xffffffffffffffff})
	github.com/go-text/[email protected]/harfbuzz/ot_shaper.go:64 +0xaa
github.com/go-text/typesetting/harfbuzz.(*otShapePlan).init0(0xc0027b6710, 0x0?, {{0x0?, 0x0?}, 0x16c4080?, 0xc0?}, {0x0, 0x0, 0x0}, {0xffffffffffffffff, ...})
	github.com/go-text/[email protected]/harfbuzz/ot_shaper.go:173 +0x7d
github.com/go-text/typesetting/harfbuzz.(*shaperOpentype).compile(...)
	github.com/go-text/[email protected]/harfbuzz/ot_shaper.go:777
github.com/go-text/typesetting/harfbuzz.newShapePlan(0xc00279e050, {{0x0?, 0x0?}, 0x13532e8?, 0xc0?}, {0x0, 0x0, 0x0}, {0x0, 0x0, ...})
	github.com/go-text/[email protected]/harfbuzz/shape.go:109 +0x145
github.com/go-text/typesetting/harfbuzz.(*Buffer).newShapePlanCached(0xc0020b6750, 0xc00279e050, {{0x0?, 0xafe497?}, 0xdde760?, 0x0?}, {0x0, 0x0, 0x0}, {0x0, ...})
	github.com/go-text/[email protected]/harfbuzz/shape.go:146 +0x369
github.com/go-text/typesetting/harfbuzz.(*Buffer).Shape(0xc0020b6750, 0xc00279e050, {0x0, 0x0, 0x0})
	github.com/go-text/[email protected]/harfbuzz/shape.go:30 +0x7f
github.com/go-text/typesetting/shaping.(*HarfbuzzShaper).Shape(0xc00135da00, {{0xc0020843c0, 0x28, 0x28}, 0x0, 0x4, 0x0, 0xc001952000, {0x0, 0x0, ...}, ...})
	github.com/go-text/[email protected]/shaping/shaping.go:113 +0x44e
fyne.io/fyne/v2/internal/painter.shapeCallback({0x1067fe0?, 0xc00135da00?}, {{0xc0020843c0, 0x28, 0x28}, 0x0, 0x4, 0x0, 0xc001952000, {0x0, ...}, ...}, ...)
	fyne.io/fyne/[email protected]/internal/painter/font.go:303 +0x7d
fyne.io/fyne/v2/internal/painter.walkString({0x1068ec0, 0xc0003f95c0}, {0xc002c361e0?, 0x0?}, 0x380, {0x1, 0x0, 0x0, 0x0, 0x0, ...}, ...)
	fyne.io/fyne/[email protected]/internal/painter/font.go:294 +0x325
fyne.io/fyne/v2/internal/painter.MeasureString({0x1068ec0?, 0xc0003f95c0?}, {0xc002c361e0?, 0x0?}, 0x0?, {0x1, 0x0, 0x0, 0x0, 0x0, ...})
	fyne.io/fyne/[email protected]/internal/painter/font.go:208 +0x6f
fyne.io/fyne/v2/internal/painter.measureText({0xc002c361e0, 0x54}, 0x41600000, {0x1, 0x0, 0x0, 0x0, 0x0, 0x0}, {0x0, ...})
	fyne.io/fyne/[email protected]/internal/painter/font.go:234 +0xb1
fyne.io/fyne/v2/internal/painter.RenderedTextSize({0xc002c361e0, 0x54}, 0x41600000, {0x1, 0x0, 0x0, 0x0, 0x0, 0x0}, {0x0, ...})
	fyne.io/fyne/[email protected]/internal/painter/font.go:219 +0xfd
fyne.io/fyne/v2/internal/driver/glfw.(*gLDriver).RenderedTextSize(0xc002839f80?, {0xc002c361e0?, 0xb9b7f1?}, 0x71a060?, {0x1, 0x0, 0x0, 0x0, 0x0, 0x0}, ...)
	fyne.io/fyne/[email protected]/internal/driver/glfw/driver.go:72 +0x8b
fyne.io/fyne/v2.MeasureText({0xc002c361e0, 0x54}, 0x41600000, {0x1, 0x0, 0x0, 0x0, 0x0, 0x0})
	fyne.io/fyne/[email protected]/text.go:72 +0x98
fyne.io/fyne/v2/widget.(*Hyperlink).syncSegments(0xc0003450e0)
	fyne.io/fyne/[email protected]/widget/hyperlink.go:296 +0x2e9
fyne.io/fyne/v2/widget.(*Hyperlink).SetText(0xc0003450e0, {0xc002c361e0, 0x54})
	fyne.io/fyne/[email protected]/widget/hyperlink.go:196 +0x8f
...

[whereswaldon]

Hmm, I guess we need a bounds check on https://github.com/go-text/typesetting/blob/v0.2.1/harfbuzz/ot_layout.go#L247

What do you think @benoitkugler? Is this another instance of a corrupt font breaking us?

[benoitkugler]

This bug seems really similar to #140.
From what I understand, the fix (#142) should also apply here, meaning upgrading the version of go-text/typesetting (at least to v0.1.1) should resolve the issue.

[andydotxyz]

Can you check if using Fyne v2.5.3 fixes the issue in your app @dweymouth ? We upgraded a couple of releases ago.

[dweymouth]

I'd have to wait for my user(s) to report back since I don't have NixOS (and I don't really intend to set up a new VM). I'll close this assuming it will have been solved, and re-open it if needed