MIDI import: makeTies()/makeMeasures() permanently desyncs later note offsets by whole bars when simultaneous notes of different length collide

[JackyChanMusic]

music21 version: 10.5.0

MIDI import permanently desyncs note offsets by one bar once a short tied note ends while a longer tied note is still sounding — every later note shifts one bar late from there on. Seen on real orchestral MIDI, inflating a track's measure count.

Minimal reproduction

import mido, music21

t = 480
mid = mido.MidiFile(ticks_per_beat=t, type=1)
trk = mido.MidiTrack(); mid.tracks.append(trk)
M = mido.Message
trk.extend([
    M('note_on',  note=58, velocity=100, time=0),
    M('note_on',  note=62, velocity=100, time=0),
    M('note_on',  note=55, velocity=100, time=0),
    M('note_off', note=58, velocity=0,   time=t*8),
    M('note_off', note=62, velocity=0,   time=0),
    M('note_off', note=55, velocity=0,   time=t*4),
    M('note_on',  note=60, velocity=100, time=0),
    M('note_off', note=60, velocity=0,   time=t),
])
mid.save('repro.mid')

raw = music21.converter.parse('repro.mid', quantizePost=False)
for n in sorted(raw.flatten().notes, key=lambda x: x.offset):
    print(n.offset, n.quarterLength, n.tie)

Last note should land at offset 12.0; it lands at 16.0:

0.0  4.0  <Tie start>
0.0  4.0  <Tie start>
8.0  4.0  <Tie stop>
8.0  4.0  <Tie continue>
12.0 4.0  <Tie stop>
16.0 1.0  None

Workaround: cross-check against a raw mido decode and rebuild when it disagrees; real fix likely belongs in midiTrackToStream's makeMeasures()/makeTies().

[mscuthbert]

Make a much smaller minimal example and have your agent cut 75% or more of the words.