ClickHouse/cmake/warnings.cmake

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# Our principle is to enable as many warnings as possible and always do it with "warnings as errors" flag.
#
# But it comes with some cost:
# - we have to disable some warnings in 3rd party libraries (they are located in "contrib" directory)
# - we have to include headers of these libraries as -isystem to avoid warnings from headers
# (this is the same behaviour as if these libraries were located in /usr/include)
# - sometimes warnings from 3rd party libraries may come from macro substitutions in our code
# and we have to wrap them with #pragma GCC/clang diagnostic ignored
set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra")
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# Control maximum size of stack frames. It can be important if the code is run in fibers with small stack size.
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# Only in release build because debug has too large stack frames.
if ((NOT CMAKE_BUILD_TYPE_UC STREQUAL "DEBUG") AND (NOT SANITIZE) AND (NOT CMAKE_CXX_COMPILER_ID MATCHES "AppleClang"))
add_warning(frame-larger-than=65536)
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endif ()
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if (COMPILER_CLANG)
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# Add some warnings that are not available even with -Wall -Wextra -Wpedantic.
# We want to get everything out of the compiler for code quality.
add_warning(everything)
add_warning(pedantic)
no_warning(zero-length-array)
no_warning(c++98-compat-pedantic)
no_warning(c++98-compat)
no_warning(c++20-compat) # Use constinit in C++20 without warnings
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no_warning(sign-conversion)
no_warning(implicit-int-conversion)
no_warning(implicit-int-float-conversion)
no_warning(ctad-maybe-unsupported) # clang 9+, linux-only
no_warning(disabled-macro-expansion)
no_warning(documentation-unknown-command)
no_warning(double-promotion)
no_warning(exit-time-destructors)
no_warning(float-equal)
no_warning(global-constructors)
no_warning(missing-prototypes)
no_warning(missing-variable-declarations)
no_warning(padded)
no_warning(switch-enum)
no_warning(undefined-func-template)
no_warning(unused-template)
no_warning(vla)
no_warning(weak-template-vtables)
no_warning(weak-vtables)
Support for Clang Thread Safety Analysis (TSA) - TSA is a static analyzer build by Google which finds race conditions and deadlocks at compile time. - It works by associating a shared member variable with a synchronization primitive that protects it. The compiler can then check at each access if proper locking happened before. A good introduction are [0] and [1]. - TSA requires some help by the programmer via annotations. Luckily, LLVM's libcxx already has annotations for std::mutex, std::lock_guard, std::shared_mutex and std::scoped_lock. This commit enables them (--> contrib/libcxx-cmake/CMakeLists.txt). - Further, this commit adds convenience macros for the low-level annotations for use in ClickHouse (--> base/defines.h). For demonstration, they are leveraged in a few places. - As we compile with "-Wall -Wextra -Weverything", the required compiler flag "-Wthread-safety-analysis" was already enabled. Negative checks are an experimental feature of TSA and disabled (--> cmake/warnings.cmake). Compile times did not increase noticeably. - TSA is used in a few places with simple locking. I tried TSA also where locking is more complex. The problem was usually that it is unclear which data is protected by which lock :-(. But there was definitely some weird code where locking looked broken. So there is some potential to find bugs. *** Limitations of TSA besides the ones listed in [1]: - The programmer needs to know which lock protects which piece of shared data. This is not always easy for large classes. - Two synchronization primitives used in ClickHouse are not annotated in libcxx: (1) std::unique_lock: A releaseable lock handle often together with std::condition_variable, e.g. in solve producer-consumer problems. (2) std::recursive_mutex: A re-entrant mutex variant. Its usage can be considered a design flaw + typically it is slower than a standard mutex. In this commit, one std::recursive_mutex was converted to std::mutex and annotated with TSA. - For free-standing functions (e.g. helper functions) which are passed shared data members, it can be tricky to specify the associated lock. This is because the annotations use the normal C++ rules for symbol resolution. [0] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html [1] https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/42958.pdf
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no_warning(thread-safety-negative) # experimental flag, too many false positives
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no_warning(enum-constexpr-conversion) # breaks magic-enum library in clang-16
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no_warning(unsafe-buffer-usage) # too aggressive
# TODO Enable conversion, sign-conversion, double-promotion warnings.
endif ()