Update go_toolchain to use execution transitons.

[katre]

No description provided.

[jayconrod]

Is cfg = "host" being renamed to cfg = "exec"? What is the minimum Bazel version that supports that?

The current minimum Bazel version for rules_go is 0.23.0, but we'll make 1.1.0 the minimum somewhat soon.

[katre]

Host and exec behave differently. Host is the current host transition: there's only one, it depends on the default flag values, and is set for building tools to be invoked on Host. The execution transition, on the other hand, allows for multiple different execution platforms and is more flexible.

Eventually I want to move everything to use the execution transition and get rid of the host, but that's not feasible anytime soon.

The execution transition was added before 1.0, but I would need to search to see what version exactly.

This draft PR was just created to run the tests and see if there are obvious failures. Do you have a way to run downstream projects with a release candidate?

[jayconrod]

Ah, interesting. My understanding was that cfg = "host" actually meant the execution platform (a misnomer from way back). So anywhere that appears in rules_go, cfg = "exec" is what's actually intended.

This draft PR was just created to run the tests and see if there are obvious failures. Do you have a way to run downstream projects with a release candidate?

I'm afraid not. Kubernetes is the biggest open source client but they're not using the most recent version. Most other clients are closed-source.

[katre]

Thanks for the additional commit. If you're fine with this change let's go ahead and commit (it should be a no-op until the actual toolchain transition changes land).

[katre]

Is there a way to kick off tests again?

[jayconrod]

Ran the tests again through BuildKite. Looks good. Thanks for sending this.

(I resurrected this since the rules_go minimum version of Bazel is now 1.2.0).

[steeve]

For the record, I ran into problems with the exec transition on my custom rules (it would fail to detect Android toolchain).
Not sure how the reason, I'll try again and report back here if I run into issues.

[jayconrod]

@steeve Interesting, please do open an issue if you're able to reproduce that.

I'm hoping to get a rules_go release out today with this, but we can do a point release if it causes problems.

[katre]

If you see an exec transition failure, please open a bug and let me know.

The change here is a no-op: toolchains are always in the host transition currently (until bazelbuild/bazel#10523 is done), and the host transition is terminal, so these cfg changes don't change anything.

[steeve]

Reviving this issue.

Having a go_binary -> cc_import -> android_binary breaks with cfg = "exec" with the following:

ERROR: /private/var/tmp/_bazel_steeve/8c5731f383ec5885e1a8afb0f4a77ff6/external/androidndk/BUILD.bazel:41:1: in cc_toolchain_suite rule @androidndk//:toolchain-libcpp: cc_toolchain_suite '@androidndk//:toolchain-libcpp' does not contain a toolchain for cpu 'darwin'

I bisected the problem down to 88bc72a. Hence me here :)

@katre do you want me to open an issue on bazel itself ?

[katre]

@steeve Can you please file an issue on Bazel with detailed reproduction steps? I'll look at is as soon as I can.

[steeve]

Sure thing!