Define an empty string in CMAKE_<LANG>_STANDARD_DEFAULT to mean that
the toolchain has no notion of lanuage standard levels. In this case
the <LANG>_STANDARD[_REQUIRED] properties will have no effect.
Update the RunCMake.CompileFeatures test to exclude the
LinkImplementationFeatureCycle test when there is no standard default.
It can never fail because no use of specific features will adjust the
CXX_STANDARD level required for any target since the standard levels
have no meaning in this case.
We require that the $<$<COMPILE_FEATURES:cxx_feature>:empty2> generates
a '1' when CXX11 is enabled. GNU 4.4 does not support cxx_nullptr, but
does support cxx_auto_type.
The second hunk of commit 07d1f6fc (Features: Properly evaluate if the
compiler supports cxx_final, 2014-12-31) was a workaround for a bug in
the COMPILE_FEATURES generator expression that caused it never to return
0. Revert the workaround so we can fix the bug instead.
Revert commits:
2d738ce3 Help: Add notes for topic 'feature_record_msvc'
f73718c9 Features: Enable writing of MSVC compiler feature header.
64c30bdc Features: Record for MSVC C++ 2015 and MSVC C 2010-2015.
225c0ef8 Features: Record for MSVC 2010-2013.
This topic was merged to master prematurely, so remove it.
Notes:
VS2015 and above are the only MSVC versions to support cxx_final, so remove
usages from the tests, and instead only test for cxx_override.
VS2012 and above to conform to cxx_decltype_incomplete_return_types
proposal, but without support for auto return types the dcl.type.simple
example in the proposal doesn't compile.
VS2013 and above to conform to the updated cxx_contextual_conversions proposal,
but VS2010 and above pass the test.
Compilers such as MSVC have no explicit flags to enable C++11 mode,
it just is always on. So only run the link tests with compilers that require
a flag to specify the language version.
Previously we expanded HAVE_FINAL to determine what the copied_file number
would be, but when we don't have cxx_final than HAVE_FINAL is not defined.
What we really want is to use expected_result.
Mark the generated source file with the GENERATED property explicitly
since it is not marked automatically as the output of any custom
command. Mark both the 0 and 1 variants so it works no matter the
outcome of the generator expression.
Allow setting build properties based on the features available
for a target. The availability of features is determined at
generate-time by evaluating the link implementation.
Ensure that the <LANG>_STANDARD determined while evaluating
COMPILE_FEATURES in the link implementation is not lower than that
provided by the INTERFACE of the link implementation. This is
similar to handling of transitive properties such as
POSITION_INDEPENDENT_CODE.
Add properties and variables corresponding to CXX equivalents.
Add features for c_function_prototypes (C90), c_restrict (C99),
c_variadic_macros (C99) and c_static_assert (C11). This feature
set can be extended later.
Add a <PREFIX>_RESTRICT symbol define to WriteCompilerDetectionHeader
to conditionally represent the c_restrict feature.
Users of the new target_compile_features command are expected to
check the existence of the CMAKE_CXX_COMPILE_FEATURES variable before
attempting to use it to require features.
This can be used to set the compiler features required by particular
targets. An error is issued at CMake time if the compiler does not
support the required feature. If a language dialect flag is required
by the features used, that will be added automatically.
Base the target_compile_features command on cmTargetPropCommandBase. This
gives us 'free' handling of IMPORTED, ALIAS, INTERFACE, non-compilable
and missing targets.
Extend the interface of the target_compile_features command with
PUBLIC and INTERFACE keywords. Populate the INTERFACE_COMPILER_FEATURES
target property if they are set. Consume the INTERFACE_COMPILER_FEATURES
target property from linked dependent targets to determine the final
required compiler features and the compile flag, if needed.
Use the same pattern of origin-debugging which is used for other
build properties.
Record the availability of this feature for GNU 4.8 on (UNIX AND
NOT APPLE) only. In the future, availability can be recorded for
earlier GNU, for other platforms and for other compilers. Initially
the affected configurations are as restricted as possible to allow
for easy testing while extending the features vector in only one
dimension.
The error message when using the set_property API directly is not
very good, but follow up commits will provide origin debugging of
the property and a target_compile_features command which will
provide a configure-time backtrace when possible.
Stephen Kelly
Brad King
Robert Maynard