Generate empty repo when path is not set

[gferon]

Declare an empty repository with empty toolchains and an error message when the path to the NDK was missing.

Based on a comment from #61 (comment) and a very similar approach to what's done in the starlark version of rules_android.

[gferon]

Note: this doesn't exactly work yet as we'd like to, as it errors with the following message

While resolving toolchains for target @@bazel_tools//tools/cpp:current_cc_toolchain (2f4faa5): toolchain type @@bazel_tools//tools/cpp:toolchain_type resolved to target @@androidndk//:error_message, but that target does not provide ToolchainInfo

[ahumesky]

It would be great to also look at how to add a test for this. It would probably require a new task in .bazelci/presubmit.yml because all the tests will set ANDROID_NDK_HOME

[ahumesky]

Hi, any update on this change?

[gferon]

@ahumesky I finally took the time to make it work as I wanted to. It involves adding a dummy_cc_toolchain like it is done in rules_rust for wasm32 (which doesn't have any CC toolchain).

I added two tests in .bazelci/presubmit.yml but don't know how to make the job expect a failure (for the hello-world-android-without-ndk variant). Could you fix that for me?

A failure will look like this (when building for Android platforms only):

bazel build //:all --platforms=//
:arm64-v8a --incompatible_enable_android_toolchain_resol
ution
INFO: Invocation ID: 45bffac4-903c-4be0-aae1-1949130af331
WARNING: Build option --platforms has changed, discarding analysis cache (this can be expensive, see https://bazel.build/advanced/performance/iteration-speed).
INFO: Analyzed target //:hello-world (83 packages loaded, 426 targets configured).
ERROR: /Volumes/bazel-cache/981d0988d8cc33709e99b10fe2f0cc90/external/rules_android_ndk~~android_ndk_repository_extension~androidndk/BUILD.bazel:48:8: Executing genrule @@rules_android_ndk~~android_ndk_repository_extension~androidndk//:invalid_android_ndk_repository_error [for tool] failed: (Exit 1): bash failed: error executing Genrule command (from target @@rules_android_ndk~~android_ndk_repository_extension~androidndk//:invalid_android_ndk_repository_error) /bin/bash -c ... (remaining 1 argument skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging

rules_android_ndk was used without a valid Android NDK being set: either the path attribute of android_ndk_repository or the ANDROID_NDK_HOME environment variable must be set.

Target //:hello-world failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 0.342s, Critical Path: 0.02s
INFO: 3 processes: 3 internal.
ERROR: Build did NOT complete successfully

[ahumesky]

Hmm yes expecting a failure in a test like this is tricky, I'm not sure that bazelci is setup up for negative tests. The alternative is to refactor the tests into "bazel within bazel test" integration tests: https://github.com/bazel-contrib/rules_bazel_integration_test

I'm not a big fan of those because they tend to very fragile and somewhat slow, but unless bazelci can do this or that's added to bazelci, might be the only option.