Fix #17796: Export correct system-distance

[rettinghaus]

Fixes #17796

[cbjeukendrup]

Looks good to me! It would be ideal if you could also add a test file for this.

[rettinghaus]

@cbjeukendrup I'm really willing to add a test, but I don't know how to get it working. Any help would be appreciated.

[cbjeukendrup]

@rettinghaus It looks like there are two options:

1. Use mxmlMscxExportTestRef. This requires a MuseScore file, and a reference XML file, i.e. testSystemDistance.mscx and testSystemDistance_ref.xml.
   • However, this method sets PREF_EXPORT_MUSICXML_EXPORTLAYOUT to false, while you want it to be true. Easiest solution might be to change the signature of mxmlMscxExportTestRef to

     void Musicxml_Tests::mxmlMscxExportTestRef(const char* file, bool exportLayout = false)

     and you can doubtlessly fill in the rest from there.
   • When saving a MSCX file in MuseScore 4, it will save a whole folder, but for the purpose of the test you can just take only the mscx file out of that folder.
2. Keep using mxmlIoTest, and make sure that the input file in the repo (i.e. testSystemDistance.xml) is exactly equal to the expected output file.
   • you can do this by looking at the diff at https://github.com/musescore/MuseScore/actions/runs/6311023321/job/17134178603?pr=19512#step:9:11130, but note that this diff is the wrong way around; contrary to what you might expect, the + lines are what's currently in the file, and the - lines are what it should be. (at least, that's my understanding right now...)

Since the purpose here is to test export, and not import/roundtrip, I think option 1 would make slightly more sense, do you agree?

[rettinghaus]

@cbjeukendrup Thanks for the tip! Works fine now.

[cbjeukendrup]

Thanks!