[cmake-developers] Idea for Multi-Toolchain Support

[Kyle Edwards]

Eric,
Thanks for the feedback. See comments below.
On Mon, 2018-12-17 at 22:06 +0100, Eric Noulard wrote:
> > 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.h
> > tml 
If you're talking about the issue of specifying multiple toolchain
files on the command line, I'm imagining a design like this:
add_toolchain(TargetToolchain FILE ${CMAKE_TOOLCHAIN_FILE_TARGET})
and then specify it on the command line with:
cmake ../src -DCMAKE_TOOLCHAIN_FILE=/path/to/host/toolchain.cmake
-DCMAKE_TOOLCHAIN_FILE_TARGET=/path/to/target/toolchain.cmake
> > 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.
If you want to build the same target with multiple toolchains then I
think you're better off declaring them as different targets, with
different TOOLCHAINs but the same source files, etc.
> > ... 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.
> 

My vision for this feature is that the project specifies the names of
the toolchains that it's expecting, and the toolchain file is agnostic
of this - it simply sets the properties of the toolchain named
${CMAKE_SELECTED_TOOLCHAIN}.
If you want to have a variable number of toolchains, you could do
something like this:
set(PROJECT_TARGET_TOOLCHAIN_NAMES "" CACHE STRING "Names of
toolchains")
foreach(i ${PROJECT_TARGET_TOOLCHAIN_NAMES})
  add_toolchain(${i} FILE ${CMAKE_TOOLCHAIN_FILE_${i}})
  add_executable(foo-${i} TOOLCHAIN ${i} ...) # Build a copy of foo for
each target platform
endforeach()
Kyle
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://cmake.org/pipermail/cmake-developers/attachments/20181217/b5745570/attachment.html>