Error No matching toolchains found for types @@bazel_tools//tools/jdk:runtime_toolchain_type. about examples HOT 7 OPEN

I'll take a look today

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@katre Is #398 related to this?

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There are two problems, lack of a CC toolchain and lack of a runtime Java toolchain

1. There's no android_ndk_repository, which means there are no Android CC toolchains available. Possibly this worked in the past but currently every Android project needs CC toolchains
2. The version of Android rules in use is v0.1.1, which is from 2018, and so is slightly out of date with Bazel at head.

I can create a PR to fix these issues.

I'm not sure when the requirement for a runtime Java toolchain was added, and I'm not sure where that should even come from. (pinging @ahumesky for advice).

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v0.1.1 of rules_android is just thin wrappers around the native android rules, so it's possible that something elsewhere within bazel changed to require this --

This is where we get the java toolchains in the starlark rules:
https://github.com/bazelbuild/rules_android/blob/5f6cc061249f8ea750f221da1ee0916cba61563f/MODULE.bazel#L8-L11

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Okay, debugged a bit further: rules_java adds runtime toolchains for various processors, including aarch64, but not for the Android OS constraint, so those aren't used. (These are created from the remote JDKs defined in rules_java/MODULE.bazel, where the target constraints are determined based on the actual name. There are no JDKs loaded for "android_aarch64", so none exist).

The JDK toolchain (not runtime) is fine, because it doesn't define any target constraints (cpu or os) (see https://github.com/bazelbuild/rules_java/blob/9cd25f0f7edc5184c4f1a10c4772ac4127f7322e/toolchains/default_java_toolchain.bzl#L181).

@ahumesky: Does the Android SDK contain a JDK for the different Android cpu flavors (in which case we just need to add the relevant toolchain configs), or do we need to download and configure a new one?

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Does the Android SDK contain a JDK for the different Android cpu flavors

I'm not sure that's what we want? There aren't JDKs for Android cpu flavors. I wonder if that what we want here is to be able to run things like robolectric tests, which exercise code built targeting a particular Android flavour on a JVM.

The approach we take for that in google3 is:

toolchain(
    name = "jdk-runtime-fake-android",
    target_compatible_with = [
        "//third_party/bazel_platforms/os:android",
    ],
    toolchain = ... # A JDK for the platform that the robolectric test executes on, e.g. linux k8
    toolchain_type = ":runtime_toolchain_type",
)

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That's a great question: all I know is "bazel thinks it wants a runtime JDK that targets android_aarch64", I haven't dug into why it wants that.

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