fix build with Qt5.14

[korli]

Resolves: https://musescore.org/en/node/299162

(short description of the changes and the motivation to make the changes)

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[Jojo-Schmitz]

You'd need to sign the CLA, else there's no chance for getting this PR merged, as far as I know.

This seems related to https://musescore.org/en/node/299162, right?

[t-bltg]

I can confirm that this PR solves https://musescore.org/en/node/299162 on a linux OS.
Thanks

[Jojo-Schmitz]

Interesting, QString::null is deprecated snce Qt 5.9 apparently, from qstring.h (from Qt 5.9.9 and 5.12.6):

#if QT_DEPRECATED_SINCE(5, 9)
    struct Null { };
    QT_DEPRECATED_X("use QString()")
    static const Null null;
    inline QString(const Null &): d(Data::sharedNull()) {}
    inline QString &operator=(const Null &) { *this = QString(); return *this; }
#endif

But why doesn't it lead to warnings using Qt 5.9 or 5.12? Anyway, that change seems to be OK

[t-bltg]

@Jojo-Schmitz It seems that one has to define QT_DEPRECATED_WARNINGS in order to throw compiler warnings.
E.g. adding to CMakeLists.txt

add_compile_definitions(QT_DEPRECATED_WARNINGS)

However, QT_DEPRECATED_WARNINGS has no effect since Qt 5.13
Source: https://doc.qt.io/qt-5/qtglobal.html#QT_DEPRECATED_WARNINGS

[Jojo-Schmitz]

Strange then how @korli found those warnings? Or did they get enabled again and possible even by default for Qt 5.14.0?

[korli]

see https://doc.qt.io/qt-5/qtglobal.html#QT_NO_DEPRECATED_WARNINGS

[Jojo-Schmitz]

So QT_DEPRECATED_WARNINGS got changed to have no effect, but at the same time QT_NO_DEPRECATED_WARNINGS got introduced to surpress those? Confusing...

[korli]

You'd need to sign the CLA, else there's no chance for getting this PR merged, as far as I know.

Done!

This seems related to https://musescore.org/en/node/299162, right?

It seems so.

[korli]

So QT_DEPRECATED_WARNINGS got changed to have no effect, but at the same time QT_NO_DEPRECATED_WARNINGS got introduced to surpress those? Confusing...

I understand that deprecation warnings become default.

[Jojo-Schmitz]

You'd need to sign the CLA, else there's no chance for getting this PR merged, as far as I know.

Done!

Thanks!

This seems related to https://musescore.org/en/node/299162, right?

It seems so.

You could use that link in the PR description under "Resolves: (direct link to the issue)", even if it is not an issue but a forum article

[korli]

You could use that link in the PR description under "Resolves: (direct link to the issue)", even if it is not an issue but a forum article

Thanks for the tip!

[dmitrio95]

Did these templates prevent MuseScore from compiling? Could you please post the error message then?

[Jojo-Schmitz]

See https://musescore.org/en/node/299162

[dmitrio95]

So this seems to be because of these lines which were added in Qt 5.14:
https://github.com/qt/qtbase/blob/5.14.0/src/corelib/serialization/qdatastream.h#L387-L395

Actually Qt implementation of these operators seems to do the same but maybe it is indeed better to be explicit here.

[korli]

Yes, Qt implementation of these operators seems to do the same but actually differs: the build fails with it. This would need investigation but changes would be more involved.