How to use libs built with cc_common.compile(...) from cc_binary?

[magnus.a...@gmail.com]

Hi,

We have a custom Starlark rule that builds some static C libraries with cc_common.compile(...) and cc_common.create_linking_context_from_compilation_outputs(...). (There are reasons why we cannot build them with normal cc_library rules, but I think that these reasons are not important for this question.)

We want to add these libraries as deps to a cc_binary rule. How do we do this?

custom_rule_that_builds_two_libs_with_cc_common_compile(

    name ="libs",

    srcs = ["file1.c", "file2.c", ...],

    ...

)

cc_binary(

    name = "program",

    deps = ? # How do we add the libs from the custom rule above as deps?

)

BR,

Magnus

[Keith Smiley]

If your rule propagates the output of those actions you can add the target name directly to the `deps` like normal.

--
Keith Smiley

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[magnus.a...@gmail.com]

Thanks Keith! May I ask you to provide more details?

Let us say that the custom rule is implemented as below. What should we return, to be able to feed it to cc_binary(deps)?

def _custom_rule_that_builds_two_libs_with_cc_common_compile_impl(...):

    # Build library1

    (compilation_context1, compilation_outputs1) = cc_common.compile(...)

    (linking_context1, linking_outputs1) = cc_common.create_linking_context_from_compilation_outputs(...)

    # Build library2

    (compilation_context2, compilation_outputs2) = cc_common.compile(...)

    (linking_context2, linking_outputs2) = cc_common.create_linking_context_from_compilation_outputs(...)

    return ??? # What to return here?

[Keith Smiley]

I think you'll need to combine those using cc_common's merge related APIs https://docs.bazel.build/versions/main/skylark/lib/cc_common.html#merge_cc_infos and then return a CcInfo constructed from that https://docs.bazel.build/versions/main/skylark/lib/CcInfo.html#CcInfo

Here's an example in the starlark implementation of cc_library https://github.com/bazelbuild/bazel/blob/26abd97974554887e9a4d140bf9f4800e23f1da8/src/main/starlark/builtins_bzl/common/cc/cc_library.bzl#L305-L310

--
Keith Smiley

To view this discussion on the web visit https://groups.google.com/d/msgid/bazel-discuss/5a66a64c-e1f2-45fd-9512-05d6c1ad9849n%40googlegroups.com.

[magnus.a...@gmail.com]

Thanks, I see. The solution in this example is to return a CcInfo with the merged output of the libraries.

My example was a bit too simplified. Our rule builds some libraries but also links some binaries. The libraries will be used by some rules, but the binaries will be used by other rules. I suppose that we cannot return one single CcInfo. Is is possible to return multiple CcInfo instances and later filter out which CcInfo to use where?

def _custom_rule_that_builds_two_libs_with_cc_common_compile_impl(...):

    ...

    return [CcInfo(library_output), CcInfo(binary_output)]

cc_binary(

    name = "rule_that_needs_libs",

    deps = ??? # Use the library CcInfo from above rule

)

some_other_rule(

     name = "rule_that_needs_bins",

     deps = ??? # Use the binary CcInfo from above rule

)

BR,

Magnus

[Keith Smiley]

At the worst case you could use OutputGroupInfo and throw your individual providers in some different fields there, but you'd probably still need to propagate _some_ CcInfo by default if you want inclusion in cc_library to "just work"

--
Keith Smiley

To view this discussion on the web visit https://groups.google.com/d/msgid/bazel-discuss/6d6f9dfe-9f59-4b9f-a0ac-dd4dae99eabdn%40googlegroups.com.

[magnus.a...@gmail.com]

Hmm, I got stuck on this problem. May I ask for some more details on how to use OutputGroupInfo (or something else) to solve the problem in the my previous post?

[Konstantin]

    output_group_1= OutputGroupInfo(

        cc_info = CcInfo(...),

    )

    output_group_2= OutputGroupInfo(

        cc_info = CcInfo(...),

    )

...

return [

            output_group_1,

            output_group_2,

            CcInfo(), # default case.

        ]

After that you can use filegroup rule to filter "output_group_1" or "output_group_2" and make subsequent rules depend on those filtering filegroup rules.

Konstantin