Wrap XML data into QString to fix encoding

[ba32107]

Fix encoding problem when exporting the database into XML format.

Type of change

• ✅ Bug fix (non-breaking change which fixes an issue)

Description and Context

Fixes #3900
Root case explained here: https://stackoverflow.com/questions/40318671/streaming-utf-8-literals-into-qtextstream
Disclaimer: I do not consider my change a proper fix. It works (correct XML is outputted), but I suspect the proper fix would be to overwrite the << operator of the TextStream class, and wrap the output into a QString there. However, I am not 100% sure about the implications of this change, so I just did this small workaround to highlight the problem for you. It fixes the original issue that was raised, but does not address the underlying problem (explained in the stack overflow article).

Testing strategy

• Manual test

Checklist:

• ✅ I have read the CONTRIBUTING document. [REQUIRED]
• ✅ My code follows the code style of this project. [REQUIRED]
• ✅ All new and existing tests passed. [REQUIRED]
• ✅ I have compiled and verified my code with -DWITH_ASAN=ON. [REQUIRED]

[droidmonkey]

The QTextStream should be setup to output in UTF-8 encoding.

[phoerious]

It outputs whatever your locale encoding is. On Linux that's usually utf-8.

[droidmonkey]

That would imply that the issue originator does not have UTF-8 as their locale?

[phoerious]

Possibly. We had similar issues with the password generator on Windows, which I fixed a while ago by forcing the console encoding to Unicode instead of cp850. L

Edit: in this specific case, it seems to be a problem with the << operator, which is supposedly fixed on Qt6. Since we are feeding constData() into the TextStream, it's const char*, not a QString. So the problem is not the output of the TextStream, but its input

[ba32107]

Edit: in this specific case, it seems to be a problem with the << operator, which is supposedly fixed on Qt6. Since we are feeding constData() into the TextStream, it's const char*, not a QString. So the problem is not the output of the TextStream, but its input

Yes indeed - that's why I said that I think the proper fix is to overwrite the << operator of TextStream and wrap every input into a QString.

[droidmonkey]

Why not just use write(..) function instead of the operator

[phoerious]

TBH, I don't like this write method. The << operator is the common idiom used everywhere and would not be clear why sometimes we use one and sometimes the other. I would prefer overloading <<. The distinction between C strings and Qt strings is bad enough as it is, we don't need to reinforce it.

[ba32107]

It seems like I reached the end of my C++ abilities - I'm unable to overwrite the << operator properly. I tried the below, but it doesn't work. Feel free to make changes to this PR.

In TextStream.h:

template<typename T>
TextStream &operator<<(T const& t);
TextStream &operator<<(const char *c);

In TextStream.cpp:

template<typename T>
TextStream &TextStream::operator<<(const T& t)
{
    return static_cast<TextStream&>(static_cast<QTextStream&>(*this) << t);
}

TextStream &TextStream::operator<<(const char* str)
{
    return static_cast<TextStream&>(*this << str);
}

[droidmonkey]

Add a comment above this line explaining that this is a workaround for a Qt issue that is resolved in Qt 6.x.

[ba32107]

Done.