Reviewgen Greenfield Controller

Review guide for KCC Greenfield controller

Please respect the following review criteria and invariants when reviewing.

1. Proto Diffs and Field Masks

• Verify that common.CompareProtoMessage is used to calculate differences between the desired state (krm spec mapped to proto) and the actual state (actual proto returned from API).
• Verify that the resulting diff paths are used to populate an UpdateMask (e.g. &fieldmaskpb.FieldMask{Paths: sets.List(paths)}) in the Update operation if required by the API.

2. Structured Reporting

• Verify that structuredreporting.ReportDiff(ctx, report) is used in the Update method to report the exact diff to the user before submitting the update request to the GCP API.

3. Mandatory Status Updates

• Strict Rule: The controller MUST always update the KRM status at the end of Create and Update operations, even if there are no fields that need updating in the GCP resource. (e.g., a setStatus(u, status) call must be present and invoked, updating ObservedState, ExternalRef, etc.).

4. Wait for LROs

• Strict Rule: For operations that return a Long Running Operation (LRO) from the GCP client, the controller MUST wait for the LRO to finish before proceeding (e.g., calling op.Wait(ctx) after Create or Update).

5. Test Coverage (Minimal and Maximal, Edge Cases)

• Ensure that the pkg/test/resourcefixture/testdata/basic/ directory for this resource contains at minimum:
  • A minimal test case (create.yaml, etc.)
  • One or more maximal test cases containing all spec fields to ensure maximal branch coverage.
• Reference Example: A good example of minimal and maximal test suites can be found here: gkehubscope.
• Check for appropriate edge-case testing if any complex logic exists in the controller (e.g., dependencies on other resources, complex identity mapping).

6. General Controller Structure & Client Creation

• Client Creation Preference: Verify that the controller uses an official GAPIC Go client library REST constructor (e.g., cloud.google.com/go/<service>/apivX via NewFooRESTClient) instead of NewFooClient (gRPC) or manually calling grpc.Dial with raw protobuf client interfaces (pb.New...Client), unless REST is unavailable or fails.
• Do Not Change Default Controller: Verify that the PR does NOT switch the default controller to direct in pkg/controller/resourceconfig/static_config.go (or via the cnrm.cloud.google.com/default-controller=direct label comment in KRM type definitions) if the resource already has an existing Terraform or DCL controller. For brownfield migrations, the existing legacy controller must remain the DefaultController for now, and the direct controller should only be added to SupportedControllers to allow side-by-side testing.
• Reference Implementation: The canonical reference controller implementation is workerpool_controller.go (Note: it predates IdentityV2 and does not handle it correctly, so ensure new controllers implement IdentityV2 properly).
• The controller must implement the directbase.Model and directbase.Adapter interfaces.
• It should contain appropriate dependency resolution (resolveDependencies).

Review Comment Template

When proposing changes or stating LGTM, format the review description as follows:

### KCC Auto-Review Results
* **Trigger criteria matched**: [Yes/No]
* **Client Creation**: [Pass/Fail] - (List if raw pb/grpc.Dial is used instead of GAPIC go-client)
* **Default Reconciler Kept**: [Pass/Fail] - (Verify that the default controller is NOT switched to direct in static_config.go or type labels if there was an existing legacy controller)
* **Proto Diffs & Update Mask**: [Pass/Fail] - (List any issues with diff calculation)
* **Structured Reporting**: [Pass/Fail] - (List if structured reporting is missing)
* **KRM Status Updates**: [Pass/Fail] - (List if status update is skipped on no-op updates)
* **LRO Wait**: [Pass/Fail] - (List if LRO waits are missing)
* **Test Coverage**: [Pass/Fail] - (List missing minimal/maximal test cases)

#### Detailed Findings / Actions Required:
1. [Specify file, line number, and exact issue]