Conan: [feature] Add a way to not apply a build requirement to other build requirements

[theodelrieu]

Hello,

After making some changes to a cross-build toolchain of mine, I wanted to try compiling the whole dependency graph locally, before pushing the changes upstream.

Therefore I went to the top-level directory and ran conan install -pr myprofile --build.
The problem is that the cross-build toolchain exposes environment flags such as CXXFLAGS.

It does work as expected for requirements, but it fails with other build requirements!

For instance, boost/1.71 from CCI build requires b2/4.0, and passing --build triggers a build of b2, which is being built with the CXXFLAGS exposed in the cross-build toolchain...

After browsing the docs about build requirements declared in profiles, it seems there is no way to express the following:

Apply this package to all consumers BUT other build requirements

And I think it should be added 😄

• [x] I've read the CONTRIBUTING guide.

[Minimonium]

Wouldn't it be better related to the https://github.com/conan-io/conan/projects/4 ?

[theodelrieu]

I guess, but it's a long road from now

[jgsogo]

PRs related to xbuild are getting traction again 😉

https://github.com/conan-io/conan/pull/5592