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Clang: Record Clang 16.0 flags for our experimental C++ modules support

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LLVM/Clang 16.0 now contains official support for what CMake needs.
This commit is contained in:
Brad King
2023-03-03 12:26:36 -05:00
parent a8b1fb7976
commit 3fe8e33f27
3 changed files with 43 additions and 21 deletions
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11
.gitlab/ci/cxx_modules_rules_clang.cmake
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@@ -1,17 +1,6 @@
set(CMake_TEST_CXXModules_UUID "a246741c-d067-4019-a8fb-3d16b0c9d1d3")
set(CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP 1)
string(CONCAT CMAKE_EXPERIMENTAL_CXX_SCANDEP_SOURCE
"${CMAKE_CXX_COMPILER_CLANG_SCAN_DEPS}"
" -format=p1689"
" --"
" <CMAKE_CXX_COMPILER> <DEFINES> <INCLUDES> <FLAGS>"
" -x c++ <SOURCE> -c -o <OBJECT>"
" -MT <DYNDEP_FILE>"
" -MD -MF <DEP_FILE>"
" > <DYNDEP_FILE>")
set(CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FORMAT "clang")
set(CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FLAG "@<MODULE_MAP_FILE>")
# Default to C++ extensions being off. Clang's modules support have trouble
# with extensions right now.

39
Help/dev/experimental.rst
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@@ -57,17 +57,36 @@ dependency scanning. This is similar to the Fortran modules support, but
relies on external tools to scan C++20 translation units for module
dependencies. The approach is described by Kitware's `D1483r1`_ paper.
The ``CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP`` variable can be set to ``1``
in order to activate this undocumented experimental infrastructure. This
is **intended to make the functionality available to compiler writers** so
they can use it to develop and test their dependency scanning tool.
The ``CMAKE_EXPERIMENTAL_CXX_SCANDEP_SOURCE`` variable must also be set
to tell CMake how to invoke the C++20 module dependency scanning tool.
In order to activate CMake's experimental support for C++20 module
dependencies, set the following variables:
MSVC 19.34 (provided with Visual Studio 17.4) and above contains the support
that CMake needs and has these variables already set up as required and only
the UUID and the ``CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP`` variables need to be
set.
``CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API``
Set this to the UUID documented above.
``CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP``
Set this to ``1`` in order to activate this undocumented experimental
infrastructure. This is **intended to make the functionality available
to compiler writers** so they can use it to develop and test their
dependency scanning tool.
Some compilers already have support for module dependency scanning:
* MSVC 19.34 and newer (provided with Visual Studio 17.4 and newer)
* LLVM/Clang 16.0 and newer
For those, only the above variables need to be set by project code.
For compilers with in-development support, additional variables must
be set as follows.
``CMAKE_EXPERIMENTAL_CXX_SCANDEP_SOURCE``
Set this to tell CMake how to invoke the C++20 module dependency
scanning tool.
``CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FORMAT``
Set this for compilers that generate module maps. See below.
``CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FLAG``
Set this for compilers that generate module maps. See below.
For example, add code like the following to a test project:

14
Modules/Compiler/Clang-CXX.cmake
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@@ -29,3 +29,17 @@ if("x${CMAKE_CXX_COMPILER_FRONTEND_VARIANT}" STREQUAL "xMSVC")
set(CMAKE_CXX_DEPENDS_USE_COMPILER TRUE)
endif()
endif()
if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 16.0)
string(CONCAT CMAKE_EXPERIMENTAL_CXX_SCANDEP_SOURCE
"${CMAKE_CXX_COMPILER_CLANG_SCAN_DEPS}"
" -format=p1689"
" --"
" <CMAKE_CXX_COMPILER> <DEFINES> <INCLUDES> <FLAGS>"
" -x c++ <SOURCE> -c -o <OBJECT>"
" -MT <DYNDEP_FILE>"
" -MD -MF <DEP_FILE>"
" > <DYNDEP_FILE>")
set(CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FORMAT "clang")
set(CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FLAG "@<MODULE_MAP_FILE>")
endif ()