Add Resource Plan Validation Funcion `ValidatePlan`

[zliang-akamai]

The framework only support ValidateConfig function for now, and in some cases, a non-computed attributes may still be an unknown value in the config value during validation time.

Having a ValidatePlan function may solve this problem.

[austinvalle]

Hey there @zliang-akamai 👋🏻 ,

It's true that validation in Terraform can receive configuration values that are unknown (for example, if you're running terraform validate and referencing a new resource's attribute that is computed). However, Terraform guarantees to eventually call validation with a fully known config before applying the resource.

So if you were running terraform apply on a configuration that had unknowns values, you should expect to see multiple executions of ValidateConfig, where the final execution has a fully known config. That's why we typically recommend validation logic not error when encountering unknown values, because it's guaranteed to eventually be known: https://developer.hashicorp.com/terraform/plugin/framework/validation

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Are you observing different behavior then what I mentioned above? If so, this might be a bug.

[zliang-akamai]

Hi @austinvalle, thanks for the information! I think this is a good solution for the problem.