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Genex: Enable COMPILE_LANGUAGE for COMPILE_DEFINITIONS with VS and Xcode

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The set of compile flags used for a target's C and C++ sources is based
on the linker language.  By default this is always the C++ flags if any
C++ sources appear in the target, and otherwise the C flags.  Therefore
we can define the `COMPILE_LANGUAGE` generator expression in
`COMPILE_DEFINITIONS` to match the selected language.

This is not exactly the same as for other generators, but is the best VS
and Xcode can do.  It is also sufficient for many use cases since the
set of definitions for C and C++ is frequently similar but may be
distinct from those for other languages like CUDA.

Issue: #17435
This commit is contained in:
Brad King
2018-01-11 11:23:06 -05:00
parent 0795d25b78
commit c2f79c9867
24 changed files with 107 additions and 115 deletions
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27
Help/manual/cmake-generator-expressions.7.rst
View File

@@ -97,10 +97,9 @@ Available logical expressions are:
compile features and a list of supported compilers.
``$<COMPILE_LANGUAGE:lang>``
``1`` when the language used for compilation unit matches ``lang``,
otherwise ``0``. This expression may be used to specify compile options for
source files of a particular language in a target. For example, to specify
the use of the ``-fno-exceptions`` compile option (compiler id checks
elided):
otherwise ``0``. This expression may be used to specify compile options
and compile definitions for source files of a
particular language in a target. For example:
.. code-block:: cmake
@@ -108,10 +107,20 @@ Available logical expressions are:
target_compile_options(myapp
PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-fno-exceptions>
)
target_compile_definitions(myapp
PRIVATE $<$<COMPILE_LANGUAGE:CXX>:COMPILING_CXX>
)
Note that with :ref:`Visual Studio Generators` there is no way to represent
This specifies the use of the ``-fno-exceptions`` compile option
and ``COMPILING_CXX`` compile definition for C++ only
(compiler id checks elided).
Note that with :ref:`Visual Studio Generators` and :generator:`Xcode` there
is no way to represent target-wide compile definitions separately for
``C`` and ``CXX`` languages.
Also, with :ref:`Visual Studio Generators` there is no way to represent
target-wide flags separately for ``C`` and ``CXX`` languages. Under these
generators, target-wide flags for both C and C++ sources will be evaluated
generators, expressions for both C and C++ sources will be evaluated
using ``CXX`` if there are any C++ sources and otherwise using ``C``.
A workaround is to create separate libraries for each source file language
instead:
@@ -125,15 +134,11 @@ Available logical expressions are:
target_link_libraries(myapp myapp_c myapp_cxx)
The ``Makefile`` and ``Ninja`` based generators can also use this
expression to specify compile-language specific compile definitions
and include directories:
expression to specify compile-language specific include directories:
.. code-block:: cmake
add_executable(myapp main.cpp foo.c bar.cpp)
target_compile_definitions(myapp
PRIVATE $<$<COMPILE_LANGUAGE:CXX>:COMPILING_CXX>
)
target_include_directories(myapp
PRIVATE $<$<COMPILE_LANGUAGE:CXX>:/opt/foo/cxx_headers>
)

14
Help/release/dev/extend-compile-language-genex.rst
View File

@@ -1,7 +1,13 @@
extend-compile-language-genex
-----------------------------
* The ``COMPILE_LANGUAGE`` :manual:`generator expression
<cmake-generator-expressions(7)>` may now be used with
:ref:`Visual Studio Generators` in :prop_tgt:`COMPILE_OPTIONS`
and :command:`file(GENERATE)`.
* :ref:`Visual Studio Generators` learned to support the ``COMPILE_LANGUAGE``
:manual:`generator expression <cmake-generator-expressions(7)>` in
target-wide :prop_tgt:`COMPILE_DEFINITIONS`,
:prop_tgt:`COMPILE_OPTIONS`, and :command:`file(GENERATE)`.
* The :generator:`Xcode` generator learned to support the ``COMPILE_LANGUAGE``
:manual:`generator expression <cmake-generator-expressions(7)>` in
target-wide :prop_tgt:`COMPILE_DEFINITIONS`.
It previously supported only :prop_tgt:`COMPILE_OPTIONS` and
:command:`file(GENERATE)`.