Write only PlanModifier RequiresReplace is never executed

[yottta]

Module version

github.com/hashicorp/terraform-plugin-framework v1.16.0

Relevant provider source code

    resp.Schema = schema.Schema{
		Attributes: map[string]schema.Attribute{
			"secret_string": schema.StringAttribute{
				Optional:      true,
				WriteOnly:     true,
				PlanModifiers: []planmodifier.String{stringplanmodifier.RequiresReplace()},
			},
		},
	}

Terraform Configuration Files

terraform {
  required_providers {
    provs = {
      source = "edu/provs"
    }
  }
}

provider "provs" {
  path = "/var/tmp/custom_tf_provider"
}

resource "provs_secret" "test" {
  description = "test secret"
  secret_string = "val"
}

Expected Behavior

To satisfy this specification from the docs:

Actual Behavior

When PlanModifiers are specified for write only attributes, even if there is a configuration for the attribute, the replace of the resource does not happen which contradicts with the public docs.

Steps to Reproduce

Provider setup

1. Clone the testing provider from here.
2. Run go run ./... -debug=true
3. Save the returned TF_REATTACH_PROVIDERS to use it later

Configuration setup

With the configuration shared above, do the following:

1. Run TF_REATTACH_PROVIDERS='...' terraform apply (to create the resource)
2. Run TF_REATTACH_PROVIDERS='...' terraform apply (to see if the replace is executed which it is not)

[yottta]

The root cause is this particular condition.
Since, by design, write-only attributes have null values in the plan and also in the state, this condition will always be true, rendering the plan modifier unusable.

Provided a fix in #1227. For those who want to test this out: in the testing provider, just uncomment the replace directive from go.mod and run again the provider: go run ./... -debug=true