Replace QtDebug-based DEBUG_ASSERT implementation with C++ assert()

[Holzhaus]

No description provided.

[daschuer]

Can you describe which way the assert string goes now? Does it still end in the mixxx.log file?

[Holzhaus]

Nope, it just prints to the terminal and exits. That's the limitation.

https://en.cppreference.com/w/cpp/error/assert

[daschuer]

Mm, no good news.

What fixes this PR in addition to my branch?
Do we really need that comma feature?

Can you give an example, wat we can do with assert() and what fails with our implementation?

Can we adopt the solution from std to our version.

[coveralls]

Pull Request Test Coverage Report for Build 1052730655

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage remained the same at 29.028%

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Files with Coverage Reduction	New Missed Lines	%
src/library/proxytrackmodel.cpp	1	0%
src/util/logging.cpp	1	67.74%

Totals
Change from base Build 1052728631:	0%
Covered Lines:	20091
Relevant Lines:	69213

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💛 - Coveralls

[uklotzde]

@daschuer Can we adopt this static_cast for #4131 to prevent mistakes like using an assignment operator instead of equality comparison?

[uklotzde]

How about improving the current solution as proposed in #4131 and then as a second step prepare the migration to the assert macro?

Having the output of a debug assertion appear in the log file helps to analyze bug reports from users who are not familiar with using the command line and a debugger.

[Holzhaus]

How about improving the current solution as proposed in #4131 and then as a second step prepare the migration to the assert macro?

My original idea was to make the whole DEBUG_ASSERT infrastructure a bit easier. But this seems not feasible if we keep the requirement to log the assertion into the logfile (which is useful without a doubt).

If @daschuer fixed the issues in #4131, I'll just close this for now.