(resending now that I’ve subscribed to cmake-developers)
Hello CMake-Developers,
I’m a contributor to the LLVM project working on improving our CMake-based
build process, and I had a request I wanted to discuss with your community.
This is related to a feature request I filed
(http://public.kitware.com/Bug/view.php?id=15679
<http://public.kitware.com/Bug/view.php?id=15679>), and one of the efforts I’ve
been driving in the LLVM community
(http://lists.llvm.org/pipermail/llvm-dev/2015-July/088751.html
<http://lists.llvm.org/pipermail/llvm-dev/2015-July/088751.html>).
The complication for us is that because we’re building a compiler, and we can
be targeting multiple operating systems and architectures within the same
build, we want to be able to leverage CMake’s ability to detect the toolchain
and target capabilities, which means invoking CMake multiple times.
One of our common uses is building clang. When we build clang it is built with
the ability to target a set of architectures. We then need to use the
just-built clang to build the runtime libraries for each of the supported
targets (which may not match the host operating system or architecture).
Today we do this in a pretty horrible manner by circumventing CMake’s built-in
checks and writing custom rules for compile steps; we’re looking to improve it.
One of our big goals is that we eventually want a way to generate a single
build.ninja file that can drive a full build (including all the cross-compiled
targets). Our idea on how this would work was based on extending the
ExternalProject support in CMake.
We specifically are looking for three extensions:
(1) ExternalProject needs to prefix all the rules and targets in the ninja file
it generates so that they don't conflict with the parent project's rules or
targets
(2) ExternalProject calls to CMake need to be marked as Generator rules in
Ninja so that Ninja will re-exec itself after running CMake
(3) ExternalProject needs to generate Ninja includes in the parent project.
Doing this would allow ExternalProjects that are CMake to generate targets that
could be imported back into the parent ninja build.
Brad commented in the bug that using ExternalProject probably isn’t the best
way to accomplish this, and we’re very open to suggestions.
Thanks,
-Chris
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