[native_toolchain_c] Consider ANDROID_HOME environment variable

[simolus3]

When searching for an NDK, this now considers:

• $ANDROID_HOME/ndk/*/ directories.
• If the environment variables ANDROID_NDK, ANROID_NDK_HOME, ANDROID_NDK_LATEST_HOME or ANDROID_NDK_ROOT are set (as they are in GitHub actions), those directories.

To make this testable (it's kind of odd there's no way to patch Platform.environment with IOOverrides), this replaces the logger passed to tool resolvers with a ToolResolvingContext class that allows mocking environment variables (well, kind of. Most resolvers shell out and we can't mock that yet).

Closes #2632.

[dcharkes]

• If the environment variables ANDROID_NDK, ANROID_NDK_HOME, ANDROID_NDK_LATEST_HOME or ANDROID_NDK_ROOT are set (as they are in GitHub actions), those directories.

Some of these are filtered out in the build hooks, so we'd need to add those there too.

Thanks @simolus3! 🚀

[github-actions]

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[simolus3]

It looks like the failing health checks may be an analyzer issue? Or at least I don't understand how these changes could cause the error from the logs.

[dcharkes]

It looks like the failing health checks may be an analyzer issue? Or at least I don't understand how these changes could cause the error from the logs.

I have filed dart-lang/sdk#61870. We're not using any dot-shorthands in the code yet, so it's kinda weird.

The new tests fail on Windows, backslashes. 🙃

[simolus3]

I believe the Linux tests are failing here because we arbitrarily pick one tool out of the list returned (CompilerResolver._tryLoadToolFromNativeToolchain picks the first). So now that we find additional NDK installations, we also find outdated ones which don't generate 16KB-aligned ELF segments, which then causes test failures.

I'm not sure what the best way to fix this would be, should _AndroidNdkResolver sort NDKs by descending version number?

[dcharkes]

I believe the Linux tests are failing here because we arbitrarily pick one tool out of the list returned (CompilerResolver._tryLoadToolFromNativeToolchain picks the first). So now that we find additional NDK installations, we also find outdated ones which don't generate 16KB-aligned ELF segments, which then causes test failures.

I'm not sure what the best way to fix this would be, should _AndroidNdkResolver sort NDKs by descending version number?

Yeah that seems reasonable.

Why is the order arbitrary? I believe we should avoid this, I'd like the resolvers to have deterministic behavior. If we do file listing, we should order alphabetically (or descending if we want newest). And if we have async code we should not call .add in racy ways but rather merge lists in a predictable order.

[simolus3]

Sorry, I meant arbitrary in the sense that we pick the first one instead of one that might make more sense semantically :D I don't think there's a race here, but I'll check versions to use the latest NDK consistently.