Generated empty messages without proto.Clone.

[chhsia0]

This PR partially fixes #27.

The resource.Quantity proto message is generated from a go struct through the go-to-protobuf k8s tool. This creates two problems:

• The Quantity go struct has unexported fields, which is not cloneable through reflection, but skycfg uses proto.Clone to create empty messages. This problem is fixed in this PR by creating empty messages through reflect.New instead.
• The Quantity go struct doesn’t have any protobuf tag, but skycfg uses tags to extract field names. As a result, skycfg doesn’t not recognize resource.Quantity(string = "1000m"). To resolve this, you'll need to replace k8s.io/apimachinery in go.mod with my fork, which adds protobuf tags to the Quantity go struct:

replace k8s.io/apimachinery => github.com/chhsia0/apimachinery <k8s_version>-quantity-tag

where k8s_version can be 1.14, 1.15, 1.16 or 1.17. I'll post a PR to upstream this change.

[jmillikin-stripe]

Please file a bug against Kubernetes, asking them to use valid Protobuf implementations instead of doing their own half-baked thing. Skycfg is designed to operate on Protobuf messages, not arbitrary Go structs, and we don't have plans to support Go structs that falsely claim to be Protobuf messages.

Note that the Kubernetes code may break anyway once golang/protobuf#364 lands in upstream go-protobuf. And it will definitely not work once support for dynamic messages is implemented in go-protobuf, since at that point a message type might not be backed by any concrete Go type at all.

You may be able to work around this by updating your build workflow to generate Go source from the Kubernetes .proto files using the standard Protobuf tooling. This is what we (Stripe) do, using Bazel as our build tool. Other build tools -- Make, Rake, CMake, basically anything that can run commands -- should also be usable in this role.

[dilyevsky]

fwiw, we wrapped this thing with a special helper in Isopod (https://github.com/cruise-automation/isopod/blob/19a7f547c270318529df74a59f47bc5684837ec8/pkg/kube/util.go#L29) and never had any issues.

Examples usage:

... = corev1.ResourceRequirements(requests = {"cpu": kube.resource_quantity("1000m")})

[jbarrick-mesosphere]

Thank you @dilyevsky !