Cut/Copy/Paste multi-measure trill lines makes score with parts crash on opening

[mercuree]

Issue type

Crash or freeze

Bug description

Tested with Musescore 4.1.1 and 4.2.0 master 9bff4c6
There are two bugs related to cut/copy/paste multi-measure trill lines:

1. Without parts - if you just cut/copy/paste trill line from one note to another. It will be lost after save and reopening score.
2. With parts - if you do the same, Musescore crashes when you try to open saved musescore file with such trill line.

Steps to reproduce

Crash on opening saved score:

1. create new score (from template Treble Clef)
2. open Parts and open Piano part
3. Go back to Main score
4. enter two quarter notes, on the second note put trill line (I tested with Ornaments-> Prallprall line)
5. Extend trill line to the next measure
6. Copy/Cut trill line and paste into first note.
7. Save score.
8. Open score again
9. Crash

Trill line is missing after save and reopen:

1. create new score (from template Treble Clef)
2. enter two quarter notes, on the second note put trill line (Ornaments-> Prallprall line)
3. Extend trill line to the next measure
4. Copy/Cut trill line and paste into first note.
5. Save score.
6. Open score again
7. Trill line is missing.

Screenshots/Screen recordings

Crash on opening saved score:

trill_multimeasure_parts_crash2.mp4

Trill line is missing after save and reopen:

trill_multimeasure_lost.mp4

MuseScore Version

OS: Windows 10 Version 2009 or later, Arch.: x86_64, MuseScore version (64-bit): 4.2.0-232222302, revision: github-musescore-musescore-9bff4c6

Regression

I don't know

Operating system

OS: Windows 10 Version 2009

Additional context

Based on report https://musescore.org/en/node/353514
and score https://musescore.org/sites/musescore.org/files/2023-08/NO%20-%20Rich%20Man%27s%20Frug.mscz

[zacjansheski]

Diagnostic files for crash and MuseScore File

TrillCrash.zip

TrillCrashTest.mscz.zip

[mercuree]

Another file was reported and probably related to this issue. Multi-measure trill lines widely used here
report: https://musescore.org/en/node/356321
file: https://musescore.org/sites/musescore.org/files/2023-11/string%20quartet.mscz

report: https://musescore.org/en/node/356537
file: https://musescore.org/sites/musescore.org/files/2023-11/Nightmare%20Before%20Christmas%20Selection.mscz

[mike-spa]

Just to clarify: the crash can be fixed, and is fixed by my linked PR. However, the fact that the trill disappears can not be fixed until we properly tackle the anchors problem, which is a whole new feature expected at some point in the near future.

Also, the fact that spanners can disappear when they don't have a proper start or end element, such in this case, is a problem that dates back to probably well before Musescore 3. It's definitely not a recent regression, so I don't consider it part of the P0.

[oktophonie]

Can confirm (happily) that the PR fixes the crash with each of the scores mentioned above.

[MarcSabatella]

@mike-spa A somewhat new wrinkle here is for tempo change lines in particular, which didn't exist in MU3. Now it's easy to get into a situation where you add a rallentando or whatever starting on a given note of the top staff of a score, but that beat position doesn't contain any note or rest in another staff, as in this recent example from the forum:

The result is that the line disappears in the second part on save/reload. It's possible that at least some of the reports associatied with #19852 are due to this

In MU3, it was possible to create this sort of scenario by adding a "system line", but it wouldn't have been nearly as common a thing to do since there was no specific use case for it.

I don't know how far off a general solution to the underlying anchor problem might be, but FWIW, a workaround here is to add a secondary invisible annotation (eg, system text) on that beat. That seems to be enough to force the existence of the segment in the part, and then the line has something to attach to. So, if a real solution is still a long way off, perhaps a quick fix would be to automatically save a special invisible system text along with the line (and remove it on open). It's a hack, but from a user perspective it beats hard-to-diagnose disappearing-line bugs.