A crashing character joiner brings down the whole terminal

[Eugeny]

In particular, opentype.js cannot parse the updated Monaco font file in macOS Monterey (No valid cmap sub-tables found.), rendering xterm unusable when the ligature addon is active.

[Tyriar]

Easy repro is probably to throw in the registerCharacterJoiner callback

[jerch]

On a sidenote - the particular issue might be fixed in opentype.js v0.9.0 (see opentypejs/opentype.js#348), while font-ligatures still uses v0.8.0.

[Eugeny]

It's not unfortunately - I've tried forcibly upgrading ot.js to their latest release

[jerch]

Ah ok. Well even if it was fixed, the character joiner should not tear down the whole terminal in the first place.

[LabhanshAgrawal]

What if we create an anonymous function to try catch the handler (which returns empty array on catch) and use that instead of the actual handler at

xterm.js/src/browser/services/CharacterJoinerService.ts

Lines 71 to 74 in 2014151

	const joiner: ICharacterJoiner = {
	id: this._nextCharacterJoinerId++,
	handler
	};

Does this seem ok?

[Tyriar]

I think we just need to catch and handle exceptions here:

xterm.js/src/browser/services/CharacterJoinerService.ts

Lines 179 to 182 in 2014151

	const joinedRanges: [number, number][] = this._characterJoiners[0].handler(text);
	for (let i = 1; i < this._characterJoiners.length; i++) {
	// We merge any overlapping ranges across the different joiners
	const joinerRanges = this._characterJoiners[i].handler(text);

[LabhanshAgrawal]

Yeah, that's the only place it's called at right now, so we can update there.
I was suggesting wrapping it, so that we don't have to worry about it later, in case it's called from other places. But that might not be necessary.

Should I go ahead and open a pr for this?

[Tyriar]

@LabhanshAgrawal I think that's the only place and probably won't change. That would be great!