Author: Jonas Toth Date: 2024-12-20T14:23:24+01:00 New Revision: a9034d0b7ff3b0bf90239f6b46ada7f3490b6904
URL: https://github.com/llvm/llvm-project/commit/a9034d0b7ff3b0bf90239f6b46ada7f3490b6904 DIFF: https://github.com/llvm/llvm-project/commit/a9034d0b7ff3b0bf90239f6b46ada7f3490b6904.diff LOG: [clang-tidy][docs] improve documentation on cppcoreguidelines-narrowing-conversions (#111510) (#118209) This PR improves the docs for this check to include an example of hidden narrowing conversions from the integer promotion rules in arithmetic. Added: Modified: clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst Removed: ################################################################################ diff --git a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst index 04260e75aa558f..7cc0b2809b4589 100644 --- a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst +++ b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst @@ -27,6 +27,40 @@ This check will flag: - All applications of binary operators with a narrowing conversions. For example: ``int i; i+= 0.1;``. +Arithmetic with smaller integer types than ``int`` trigger implicit conversions, +as explained under `"Integral Promotion" on cppreference.com +<https://en.cppreference.com/w/cpp/language/implicit_conversion>`_. +This check diagnoses more instances of narrowing than the compiler warning +`-Wconversion` does. The example below demonstrates this behavior. + +.. code-block:: c++ + + // The following function definition demonstrates usage of arithmetic with + // integer types smaller than `int` and how the narrowing conversion happens + // implicitly. + void computation(short argument1, short argument2) { + // Arithmetic written by humans: + short result = argument1 + argument2; + // Arithmetic actually performed by C++: + short result = static_cast<short>(static_cast<int>(argument1) + static_cast<int>(argument2)); + } + + void recommended_resolution(short argument1, short argument2) { + short result = argument1 + argument2; + // ^ warning: narrowing conversion from 'int' to signed type 'short' is implementation-defined + + // The cppcoreguidelines recommend to resolve this issue by using the GSL + // in one of two ways. Either by a cast that throws if a loss of precision + // would occur. + short result = gsl::narrow<short>(argument1 + argument2); + // Or it can be resolved without checking the result risking invalid results. + short result = gsl::narrow_cast<short>(argument1 + argument2); + + // A classical `static_cast` will silence the warning as well if the GSL + // is not available. + short result = static_cast<short>(argument1 + argument2); + } + Options ------- _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
