[MU4 Issue] A plugin's `readScore()`, `closeScore()` and `writeScore()` fails

[Jojo-Schmitz]

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Describe the bug A plugin's readScore() fails, returning a nullptr

Same goes for closeScore() and writeScore(), they are all not yet implemented

To Reproduce Steps to reproduce the behavior:

1. Try running the Batch Convert plugin

Expected behavior Same as in MuseScore 3: read, write, close the score

Screenshots n/a

Platform information

• OS: Windows, but unlikely to be restricted to just that

Additional context See also #13162/#13582 and #8859

[johentsch]

If anyone needs a workaround for batch conversion to MuseScore 4, I wrote one which you can use by installing ms3 in your Python 3.10 environment (pip install ms3) and then calling ms3 convert -d [source_dir] -o [target_dir] -m [musescore4executable] --format mscz.

[Jojo-Schmitz]

It is not just Batch Convert that would need this, but also ABC Import.

[Jojo-Schmitz]

Is anything going to happen with this?

[jeetee]

I'm expecting a bit of the single-instance vs multi-instance logic will likely need addressing first (at least for readScore).

[Daniel63656]

Will it be possible to access all classes? In the 3.0 version Beams or Octavation lines are not exposed to the API for example

[dmitrio95]

I have created a pull request which partially restores these functions: #20822. This implementation is limited and mostly operates only on the currently opened score and the current window, but I think even such limited implementation may be useful for some import/export plugins (at least it is useful for me).