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Diffstat (limited to 'Help/manual/cmake-developer.7.rst')
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diff --git a/Help/manual/cmake-developer.7.rst b/Help/manual/cmake-developer.7.rst index 7f31970..4ab9786 100644 --- a/Help/manual/cmake-developer.7.rst +++ b/Help/manual/cmake-developer.7.rst @@ -197,6 +197,51 @@ Templates Some template code is permitted, but with some limitations. Member templates may not be used, and template friends may not be used. +Adding Compile Features +======================= + +CMake reports an error if a compiler whose features are known does not report +support for a particular requested feature. A compiler is considered to have +known features if it reports support for at least one feature. + +When adding a new compile feature to CMake, it is therefore necessary to list +support for the feature for all CompilerIds which already have one or more +feature supported, if the new feature is available for any version of the +compiler. + +When adding the first supported feature to a particular CompilerId, it is +necessary to list support for all features known to cmake (See +:variable:`CMAKE_C_COMPILE_FEATURES` and +:variable:`CMAKE_CXX_COMPILE_FEATURES` as appropriate), where available for +the compiler. + +It is sensible to record the features for the most recent version of a +particular CompilerId first, and then work backwards. It is sensible to +try to create a continuous range of versions of feature releases of the +compiler. Gaps in the range indicate incorrect features recorded for +intermediate releases. + +Generally, features are made available for a particular version if the +compiler vendor documents availability of the feature with that +version. Note that sometimes partially implemented features appear to +be functional in previous releases (such as ``cxx_constexpr`` in GNU 4.6, +though availability is documented in GNU 4.7), and sometimes compiler vendors +document availability of features, though supporting infrastructure is +not available (such as ``__has_feature(cxx_generic_lambdas)`` indicating +non-availability in Clang 3.4, though it is documented as available, and +fixed in Clang 3.5). Similar cases for other compilers and versions +need to be investigated when extending CMake to support them. + +When a vendor releases a new version of a known compiler which supports +a previously unsupported feature, and there are already known features for +that compiler, the feature should be listed as supported in CMake for +that version of the compiler as soon as reasonably possible. + +Standard-specific/compiler-specific variables such +``CMAKE_CXX98_COMPILE_FEATURES`` are deliberately not documented. They +only exist for the compiler-specific implementation of adding the ``-std`` +compile flag for compilers which need that. + Help ==== |