Capella import fails for any file containing a rest (isFullBarRest reads voice before beat is added)

[jhoevelmanns-lab]

Bug description

Loading any Capella file (.capx / CapXML) that contains a rest fails with No compatible importer found for file.

With debug logging the Capella importer gets as far as Start Parsing score.xml, then gives up. The underlying exception is:

TypeError: Cannot read properties of undefined (reading 'beats')
    at get isFullBarRest
    at Beat._calculateDuration
    at Beat.updateDurations
    at CapellaParser._parseVoice
    at CapellaParser._parseVoices

Cause

In CapellaParser._parseVoice, the rest case calls restBeat.updateDurations() before this._currentVoice.addBeat(restBeat). updateDurations() → _calculateDuration() reads isFullBarRest, which accesses this.voice.beats — but voice is not set yet, because the beat has not been added to a voice. (The chord case does the same, but there isRest is false, so the getter short-circuits before touching voice.)

case "rest":
    const restBeat = this._parseRestDurations(c.findChildElement("duration"));
    if (restBeat) {
        this._initFromPreviousBeat(restBeat, this._currentVoice);
        restBeat.updateDurations();          // <- voice is still undefined here
        this._currentVoiceState.currentPosition += restBeat.playbackDuration;
        this._currentVoice.addBeat(restBeat);

Possible fix

Either call addBeat before updateDurations for rests, or make the getter tolerant:

get isFullBarRest() {
    return this.isRest && !!this.voice && this.voice.beats.length === 1 && this.duration === Duration.Whole;
}

With the guarded getter (applied as a runtime patch on our side) the affected file loads and renders completely (26 bars).

Environment

• alphaTab 1.8.4 (npm @coderline/alphatab), browser (Chrome), useWorkers: false
• File: saved with capella 10 (<score xmlns="http://www.capella.de/CapXML/5.4">), a simple single-staff melody with eighth/quarter rests. I can't attach the original (copyrighted melody), but any CapXML file with a <rest> inside <noteObjects> should reproduce it.

Thanks for alphaTab — it's great to work with!

[github-actions]

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