I get some compiler warnings when I compile SQLite. Isn't this a problem?
    Doesn't it indicate poor code quality?

    Quality assurance in SQLite is done using full-coverage testing, not by
    compiler warnings or other static code analysis tools. In other words, we
    verify that SQLite actually gets the correct answer, not that it merely
    satisfies stylistic constraints. Most of the SQLite code base is devoted
    purely to testing. The SQLite test suite runs tens of thousands of separate
    test cases and many of those test cases are parameterized so that hundreds
    of millions of tests involving billions of SQL statements are run and
    evaluated for correctness prior to every release. The developers use code
    coverage tools to verify that all paths through the code are tested.
    Whenever a bug is found in SQLite, new test cases are written to exhibit
    the bug so that the bug cannot recur undetected in the future.

    During testing, the SQLite library is compiled with special instrumentation
    that allows the test scripts to simulate a wide variety of failures in
    order to verify that SQLite recovers correctly. Memory allocation is
    carefully tracked and no memory leaks occur, even following memory
    allocation failures. A custom VFS layer is used to simulate operating
    system crashes and power failures in order to ensure that transactions are
    atomic across these events. A mechanism for deliberately injecting I/O
    errors shows that SQLite is resilient to such malfunctions. (As an
    experiment, try inducing these kinds of errors on other SQL database
    engines and see what happens!)

    We also run SQLite using Valgrind on Linux and verify that it detects no
    problems.

    Some people say that we should eliminate all warnings because benign
    warnings mask real warnings that might arise in future changes. This is
    true enough. But in reply, the developers observe that all warnings have
    already been fixed in the builds used for SQLite development (various
    versions of GCC, MSVC, and clang). Compiler warnings usually only arise
    from compilers or compile-time options that the SQLite developers do not
    use themselves.

https://www.sqlite.org/faq.html#q17

Thanks for posting that, very interesting. I don't think it's entirely fair. No one should care about warnings about style (spacing, case, etc), but much more commonly warnings about correctness are important.

SQLite is indeed nothing short of amazing with regard to the testing they have.