manifest: add support for explicit elements in `computedFields`

[BBBmau]

Description

We only support computedFields attributes, if a user attempts to be explicit with computedFields they will get a vanished output:

│ Error: Provider produced inconsistent result after apply
│ 
│ When applying changes to kubernetes_manifest.deployment_resource_diff, provider
│ "provider[\"registry.terraform.io/hashicorp/kubernetes\"]" produced an unexpected new value:
│ .object.spec.template.spec.containers[0].resources.limits: element "cpu" has vanished.
│ 
│ This is a bug in the provider, which should be reported in the provider's own issue tracker.

What's the value in being able to support this? Of course the work around is to just set the attribute as computedFields where the element exists, though it also would be good to give users that option of being explicit also.

A related issue where a user brings this up, advice was to just set attributes to computedFields

https://github.com/hashicorp/terraform-provider-kubernetes/issues/1530

Potential Terraform Configuration

Any tfconfig will do where you attempt to set an element in computedFields

resource "kubernetes_manifest" "deployment_resource_diff" {
computed_fields = ["spec.template.spec.containers[0].resources.limits[\"cpu\"]"]
    manifest = {
        apiVersion = "apps/v1"
        kind       = "Deployment"

        metadata = {
            name = "deployment-resource-diff"
            namespace = "default"
        }

        spec = {
    replicas = 3

    selector = {
      matchLabels = {
        test = "MyExampleApp"
      }
    }

    template = {
      metadata= {
        labels = {
          test = "MyExampleApp"
        }
      }
      

      spec = {
        containers = [{
          image = "nginx:1.21.6"
          name  = "example"

          resources = {
            limits = {
              cpu    = "0.5"
              memory = "512Mi"
            }
            requests = {
              cpu    = "250m"
              memory = "50Mi"
            }
          }
        }]
      }
    }
  }
        }
    }

References

Community Note

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[theloneexplorerquest]

I am interested to work on this 😃

[theloneexplorerquest]

just some progress update: I have identified code block that causing this issue. I suspect the issue is in terraform-plugin-go, will do some further investigation.

[alexsomesan]

@theloneexplorerquest be advised that @BBBmau is also working on an improvement in this direction. It would be good to coordinate, to not waste effort.

[theloneexplorerquest]

@BBBmau @alexsomesan thanks for let me know, I try to get involved in OSS only on weekend (and I slack off sometimes 😅), so my pace is slow. Here is my investigation so far: The code call https://github.com/hashicorp/terraform-provider-kubernetes/blob/main/manifest/provider/apply.go#L198 leads to error out at https://github.com/hashicorp/terraform-plugin-go/blob/main/tftypes/value.go#L156 when the input path ap is spec.containers.0.resources.limits.cpu, note the last element is determined as ElementKeyString however the others are AttributeName it appears we cannot convert the corresponding value of cpu to val.Type().(Map) for some reason. If I change https://github.com/hashicorp/terraform-plugin-go/blob/main/tftypes/value.go#L156 to val.Type().(Object), everything starts to work again. So, my guess is either we pass the wrong parameter in tftypes.WalkAttributePath or there is a bug in terraform-plugin-go.

I will work on something else for now, let me know if you need further details. :blush: