User provided platform constraints

[nickjmeyer]

Hello,

Using this repo, I currently have a tool chain set up to build for target Linux x86_64 and Linux aarch64 all on a host Linux x86_64 machine. I have a third platform I need to support that is another Linux aarch64 target. Is there a way to provide additional platform constraints to enable defining multiple platforms with the same target arch / os? From reading through the repository, it appears not given the exec_compatible_with attribute is set to only specify os and arch.

If not supported, any code pointers as to how you'd extend it to do so?

[fmeum]

This could be wired up in a similar way to target_settings defined here: https://github.com/bazel-contrib/toolchains_llvm/blob/e3c57fc322e684daa656444cbc01435fa0884707/toolchain/internal/repo.bzl#L240

The LLVM extension could receive new tag_classes for, say, extra_target_compatible_with and extra_exec_compatible_with that are similar to the ones defined here (just taking an attr.label_list instead of an attr.label: https://github.com/bazel-contrib/toolchains_llvm/blob/e3c57fc322e684daa656444cbc01435fa0884707/toolchain/extensions/llvm.bzl#L82-L89

[jkurland-roku]

I've opened an MR with an implementation of this here (https://github.com/bazel-contrib/toolchains_llvm/pull/371).

[nickjmeyer]

Thanks for the pointers!