How to use "frameworks" for mac builds?

[miaoyipu]

Hi, new to the buck on Mac. I am adding "-framework SomeFramework" to the link flag on Mac (can be implemented by exported_link_flags). So I added the framework to the hello world, like

cxx_library(
    name = "print",
    srcs = glob(["**/*.cpp"]),
    exported_headers = glob(["**/*.hpp"]),
    visibility = ["PUBLIC"],
    frameworks = [
        '$SDKROOT/System/Library/CoreAudio.framework',
    ],
)

I am seeing missing apple toolchain error

4: Traceback (most recent call last):
         File <builtin>, in <module>
         * prelude/cxx/cxx.bzl:169, in cxx_library_impl
             output = cxx_library_parameterized(ctx, params)
         * prelude/cxx/cxx_library.bzl:427, in cxx_library_parameterized
             shared_links, link_group_map, link_execution_preference = _get_shared_library...
         * prelude/cxx/cxx_library.bzl:1067, in _get_shared_library_links
             return apple_build_link_args_with_deduped_flags(
         * prelude/apple/apple_frameworks.bzl:135, in apple_build_link_args_with_deduped_flags
             link_info = _link_info_from_linkables(ctx, [merged.frameworks[link_style], fr...
         * prelude/apple/apple_frameworks.bzl:194, in _link_info_from_linkables
             framework_link_args = _get_apple_frameworks_linker_flags(ctx, merge_framework...
         * prelude/apple/apple_frameworks.bzl:50, in _get_apple_frameworks_linker_flags
             expanded_frameworks_paths = _expand_sdk_framework_paths(ctx, linkable.unresol...
         * prelude/apple/apple_frameworks.bzl:92, in _expand_sdk_framework_paths
             return [_expand_sdk_framework_path(ctx, unresolved_framework_path) for unreso...
       error: Object of type `struct` has no attribute `_apple_toolchain`
         --> prelude/apple/apple_frameworks.bzl:95:28
          |
       95 |     apple_toolchain_info = ctx.attrs._apple_toolchain[AppleToolchainInfo]
          |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^
          |

How should I make this work and passing apple_toolchain ?

[zjturner]

I think you need to return one of these from your toolchain.

https://github.com/facebook/buck2/blob/56c1bcf08bb793a5314d7739b090b6d173314cde/prelude/apple/apple_toolchain_types.bzl#L8C1-L39

If you're using system_cxx_toolchain(), it doesn't do that so you would need to define a custom apple toolchain that does (or alternatively, patch system_cxx_toolchain()). The semantics of each of the fields isn't really documented, so it might take some work to figure out exactly what each field is supposed to do by looking for how each one is used. At least they are annotated with the intended type of the field.

This is the kind of thing that if you can figure out exactly how to use each field, upstreaming a patch to add comments to each fields describing how to use them would be super valuable.