digest function capability check does not consider all available ExecutionCapabilities.DigestFunctions

[werkt]

remote-apis-sdks' capabilities verification test only observes the ExecutionCapabilities.DigestFunction response to capabilities for compatibility, which reclient relies upon.

This prevents servers which indicate multiple DigestFunctions in the same record from using reclient (and other remote-api-sdks consumers) with any of the available DigestFunctions.

https://github.com/bazelbuild/remote-apis-sdks/blob/master/go/pkg/digest/digest.go#L182

This should be testing for the specified digest function presence in DigestFunctions, and using it, likely ignoring the legacy digest_function field. See the comments around these fields and their evolution here: https://github.com/bazelbuild/remote-apis/blob/main/build/bazel/remote/execution/v2/remote_execution.proto#L2062-L2091

[mrahs]

Thank you for surfacing this limitation. It looks like the remote execution API has been updated after the implementation in this SDK. I'd be happy to review a PR to support the newer API.