Le lun. 17 déc. 2018 à 22:04, Eric Noulard <eric.noul...@gmail.com> a écrit :
> Hi Kyle, > > Is your proposal a follow-up on the initial bunch of ideas launched in > this thread launch by Eike in November > https://cmake.org/pipermail/cmake-developers/2018-November/030913.html > with follow-up ideas in in december: > https://cmake.org/pipermail/cmake-developers/2018-December/030920.html > > or is it somehow unrelated? > > > Le lun. 17 déc. 2018 à 21:18, Kyle Edwards via cmake-developers < > cmake-developers@cmake.org> a écrit : > >> Hello everyone, >> >> One of the things that's long been requested of CMake is the ability to >> have multiple toolchains - for instance, one host toolchain and one >> cross toolchain, so that "utilities" needed for build can be built with >> the host toolchain and then the "real" software can be built with the >> cross toolchain. >> >> To solve this problem, I would like to propose the creation of a new >> first-class object type, the "toolchain" type, which would replace the >> current variable-based system, similar to how imported targets replaced >> variable-based usage requirements. >> >> Every project would automatically receive one toolchain, the "DEFAULT" >> toolchain, which would be either automatically configured or configured >> based on CMAKE_TOOLCHAIN_FILE, just like the current system. New >> toolchains could be added with the add_toolchain() command: >> >> add_toolchain(CrossToolchain FILE /path/to/toolchain/file.cmake) >> > > This has some common design issue as my proposal: > enable_cross_target(...) > for which Eike has valuable doubt: > https://cmake.org/pipermail/cmake-developers/2018-November/030919.html > > >> Then, executables and libraries could have a toolchain specified: >> >> add_executable(BuildUtility TOOLCHAIN DEFAULT ...) >> add_library(MyLibrary TOOLCHAIN CrossToolchain ...) >> >> Note that the TOOLCHAIN argument is optional, and if omitted, the >> DEFAULT toolchain is used. >> > > So if you want to build both for host and cross toolchain you'll have to > explicitely > add_executable/library(MyLibrary TOOLCHAIN DEFAULT) > add_executable/library(MyLibrary TOOLCHAIN CrossToolchain) > > If you follow the previously referred discussion you cannot assume that > one lib/exe > built for a toolchain is not built for another toolchain as well. > > How do you envision the cross-toolchain target dependency which was > a question raised several time. > > >> If a project uses multiple toolchains, we could have the option to >> rename the default toolchain with an alternative add_toolchain() >> syntax: >> >> add_toolchain(HostToolchain DEFAULT) >> >> Rather than adding a new toolchain, this would simply rename the >> "DEFAULT" toolchain to "HostToolchain". Then the toolchain >> specification for each target could look like this: >> >> add_executable(BuildUtility TOOLCHAIN HostToolchain ...) >> add_library(MyLibrary TOOLCHAIN CrossToolchain ...) >> >> Two new global read-only properties would be added: TOOLCHAINS and >> DEFAULT_TOOLCHAIN. TOOLCHAINS would be a semicolon-separated list of >> all registered toolchains, and DEFAULT_TOOLCHAIN would be the name of >> the DEFAULT toolchain (which could be changed with the alternative >> add_toolchain() syntax.) >> >> The CMAKE_TOOLCHAIN_FILE format would be changed so that rather than >> setting variables: >> >> set(CMAKE_C_COMPILER /usr/bin/gcc) >> set(CMAKE_C_COMPILER_ID gnu) >> # etc. >> >> it would instead set properties on the selected toolchain: >> >> set_property(TOOLCHAIN ${CMAKE_SELECTED_TOOLCHAIN} PROPERTY C_COMPILER >> /usr/bin/gcc) >> set_property(TOOLCHAIN ${CMAKE_SELECTED_TOOLCHAIN} PROPERTY >> C_COMPILER_ID gnu) >> # etc. >> > > I don't see why we should change the syntax of current toolchain file, I > don't see the benefit. > CMake already knows when (and which) toolchain file is loaded and it could > perfectly automatically > ... sorry wrong key pressed... CMake could perfectly automatically create the new "TOOLCHAIN" object by loading the very same toolchain file as we have today. We could simple add a new variable CMAKE_TOOLCHAIN_NAME in that file so that CMake (and the user) can name them as he wants. When there is no CMAKE_TOOLCHAIN_NAME this would be the default toolchain. -- Eric
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