Add rules_foreign_cc example

[keith]

No description provided.

[keith]

this is failing on macOS, which I lightly started debugging, not sure what the issue is, but there's clearly a mismatch in toolchain selection or something so the cmake invocation is getting macOS args

[keith]

related bazel-contrib/rules_foreign_cc#289, but I don't know why this works fine with the bazel core NDK infra and not this repo

[ahumesky]

this is failing on macOS, which I lightly started debugging, not sure what the issue is, but there's clearly a mismatch in toolchain selection or something so the cmake invocation is getting macOS args

I'll see if anyone might have an idea of what's going on

[keith]

thanks that's where I'm surprised that something changed here, but I haven't dug super deep. I imagine someone more familiar with these toolchain setups would know the issue off the top of their head

[keith]

@ahumesky you hear any useful tips?

[ahumesky]

Let me follow up on some threads.
I took a quick look at the errors, and yeah I'm not sure where -search_paths_first is coming from, it's not part of rules_android_ndk, and I didn't find it in bazel's codebase either

[keith]

cmake default https://github.com/Kitware/CMake/blob/239beca1e3743ec693643869621cd0e41ed10a16/Modules/Platform/Darwin.cmake#L60 added since it's picking the wrong platform for sure

[ahumesky]

and you're not able to repro this locally i assume right?

[keith]

oh i think it repros locally too yea. it's definitely a difference in the toolchain configuration somewhere

[ahumesky]

ah ok that's good -- much harder if it just repros on CI

[ahumesky]

I think the problem basically comes down to this:
https://github.com/Kitware/CMake/blob/239beca1e3743ec693643869621cd0e41ed10a16/Modules/Platform/Darwin.cmake#L31-L38

rules_foreign_cc / cmake / cmake() is just going to evaluate that and add the flag based on just the version of the OS. There's nothing connecting that to the fact that this is actually an android build with a different compiler. Is there a way to define HAVE_FLAG_SEARCH_PATHS_FIRST with a value of 0 in the cmake() target?

[keith]

it's not just about that flag though, you can see it's adding many macOS specific flags like -isysroot /Applications/Xcode13.0.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.3.sdk too. I think the general problem is that rules_foreign_cc tries to use something from the toolchain to indicate the platform and whatever that is differs with this vs the native one

[ahumesky]

oh i didn't realize there were more problematic values in there.

the cmake() rule is grabbing the cpp toolchain:
https://github.com/bazelbuild/rules_foreign_cc/blob/2c6262f8f487cd3481db27e2c509d9e6d30bfe53/foreign_cc/private/framework.bzl#L464

and I believe this is all going through the legacy toolchain resolution (especially with --noincompatible_enable_cc_toolchain_resolution still being used here) -- which I think ends up using --crosstool_top, can you try setting that in addition to --android_crosstool_top? (you may also then have to set --host_crosstool_top so that the host tools don't try to use the android crosstool as well)

[ahumesky]

hmm, although, there's a split transition on android_binary which should have translated --android_crosstool_top to --crosstool_top for its dependencies -- including the cmake() target... so even if setting --crosstool_top makes this work, then there's still more to discover here

[keith]

yea avoiding with crosstool_top doesn't work and actually seems to cause more issues:

% bazel build //java/com/app:app --crosstool_top=@androidndk//:toolchain --host_crosstool_top=@bazel_tools//tools/cpp:toolchain
ERROR: /private/var/tmp/_bazel_ksmiley/55ec32113415a74e2950047844b9eb9d/external/androidndk/toolchains/llvm/prebuilt/darwin-x86_64/BUILD:20:19: in cc_toolchain_suite rule @androidndk//toolchains/llvm/prebuilt/darwin-x86_64:cc_toolchain_suite: cc_toolchain_suite '@androidndk//toolchains/llvm/prebuilt/darwin-x86_64:cc_toolchain_suite' does not contain a toolchain for cpu 'darwin_arm64'
ERROR: /private/var/tmp/_bazel_ksmiley/55ec32113415a74e2950047844b9eb9d/external/androidndk/toolchains/llvm/prebuilt/darwin-x86_64/BUILD:20:19: Analysis of target '@androidndk//toolchains/llvm/prebuilt/darwin-x86_64:cc_toolchain_suite' failed
ERROR: Analysis of target '//java/com/app:app' failed; build aborted:
INFO: Elapsed time: 0.099s
INFO: 0 processes.
FAILED: Build did NOT complete successfully (0 packages loaded, 0 targets configured)

[keith]

Ok actually I think this is just a rules_foreign_cc issue that wasn't a huge deal before but was uncovered because of switching to lld in the NDK. Tracking here bazel-contrib/rules_foreign_cc#289

[keith]

@ahumesky can you review this one?