DiffSuppressFunc alternative?

[amalavet]

Module version

v1.11.0

Use-cases

To keep our plans less verbose, we'd like to be able to obscure/shorten the diff for some of our attributes on our resources.

Attempted Solutions

1. Setting sensitive obscures the diff, but we want to obscure non-sensitive fields as well
2. I have attempted to use a plan modifier, but this impacts the value that gets applied to the state as well.

"my_field": schema.StringAttribute{
	...
        Sensitive: true,
},

type suppressFieldValue struct{}

func (m suppressFieldValue) Description(_ context.Context) string {
	return "Suppresses the value within the plan"
}

func (m suppressFieldValue) MarkdownDescription(_ context.Context) string {
	return "Suppresses the value within the plan"
}

func (m suppressFieldValue) PlanModifyString(
	_ context.Context,
	req planmodifier.StringRequest,
	resp *planmodifier.StringResponse,
) {
	resp.PlanValue = types.StringValue("<<SUPPRESSED>>")
}

Proposal

We could have an optional value that, if set, overrides the diff of the attribute within the plan?

... 
func (m suppressFieldValue) PlanModifyString(
	_ context.Context,
	req planmodifier.StringRequest,
	resp *planmodifier.StringResponse,
) {
	resp.PlanDiffValue = types.StringValue("<<SUPPRESSED>>")
}

or just do something like: DiffSuppressFunc from sdkv2

References

• CustomizeDiff functionality in framework #859
• https://discuss.hashicorp.com/t/diffsuppressfunc-alternative-in-terraform-framework/52578/5
• https://developer.hashicorp.com/terraform/plugin/framework/resources/plan-modification#creating-attribute-plan-modifiers
• https://developer.hashicorp.com/terraform/plugin/sdkv2/schemas/schema-behaviors#diffsuppressfunc

[austinvalle]

Hey there @amalavet 👋🏻!

The valid use-cases of DiffSuppressFunc were replaced by framework with custom type semantic equality, although I believe what you're describing would be considered invalid to Terraform from a data consistency perspective. The general rules for managed resource plan/apply are fully described here: https://github.com/hashicorp/terraform/blob/main/docs/resource-instance-change-lifecycle.md.

For apply, we'd end up breaking this rule:

Any attribute that had a known value in the Final Planned State must have an identical value in the new state.

If we plan a suppressed/different value then it is required by the Terraform provider to return this exact value in state as well.

If the attribute you're describing is a configuration value, you also are not able to plan a value that does not exactly match configuration or the prior state value:

Any attribute that was non-null in the configuration must either preserve the exact configuration value or return the corresponding attribute value from the prior state.

---

DiffSuppressFunc is able to do what you've described because data consistency rules are not applied to SDKv2 for compatibility reasons: https://developer.hashicorp.com/terraform/plugin/sdkv2/resources/data-consistency-errors