Expect cxx_variadic_templates to implement N2555.
N2555 is essentially a bugfix and predates most compiler releases which
aimed to experimentally support variadic templates.
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.
Use the contents of it to upgrade the CXX_STANDARD target property,
if appropriate. This will have the effect of adding the -std=c++11
compile flag or other language specification on GNU when that is
needed for the feature.
Add a feature test using the compiler macros and the preprocessor to
determine available features.
Add a CMAKE_CXX_COMPILE_FEATURES variable which contains all features
known to the loaded compiler, and a CMAKE_CXX_KNOWN_FEATURES variable
containing all features known to CMake. Add language standard specific
variables for internal use to determine the standard-specific compile
flags to use.
This will be extended to other languages in the future. Follow-up
commits will add features which will be recorded by the feature test.
a4e6bf8e cmTarget: Make GetSourceFiles string overload private.
92e2fbe1 cmGeneratorTarget: Trace cmSourceFile objects instead of strings.
c5b26f3b cmTarget: Cache the cmSourceFiles in GetSourceFiles.
eb163f37 cmTarget: Extract a ProcessSourceItemCMP0049 method.
19b7c22d Ninja: Query custom commands once per target, not once per file.
This reverses the decision in commit d38423ec (cmTarget: Add a
method to obtain list of filenames for sources., 2014-03-17). The
cmSourceFile based API is preferred because that avoids creation of
many cmSourceFileLocation objects for matching strings, and the
result is cached by cmTarget.
Avoid calling GetSourceFiles with the same result container multiple
times when tracing target dependencies. The result from the previous
configuration is cached and used later otherwise.
Avoid calling AddSource for each src filename. That involves
checking each entry for uniqueness and creating a separate
generator expression for each one.
Instead, add a single entry for the list of sources. The source
files are passed through a uniqueness filter at generate-time, so
duplicates don't matter so much.
Stephen Kelly
Brad King
Kitware Robot