Rename to UseStateForUnknown.

.changelog/204.txt

@@ -1,3 +1,3 @@
 ```release-note:feature
-Added `tfsdk.PreserveState()` as a built-in plan modifier, which will automatically replace an unknown value in the plan with the value from the state. This mimics the behavior of computed and optional+computed values in Terraform Plugin SDK versions 1 and 2. Provider developers will likely want to use it for "write-once" attributes that never change once they're set in state.
+Added `tfsdk.UseStateForUnknown()` as a built-in plan modifier, which will automatically replace an unknown value in the plan with the value from the state. This mimics the behavior of computed and optional+computed values in Terraform Plugin SDK versions 1 and 2. Provider developers will likely want to use it for "write-once" attributes that never change once they're set in state.
 ```

tfsdk/attribute_plan_modification.go

@@ -119,24 +119,24 @@ func (r RequiresReplaceIfModifier) MarkdownDescription(ctx context.Context) stri
 	return r.markdownDescription
 }
 
-// PreserveState returns a PreserveStateModifier.
-func PreserveState() AttributePlanModifier {
-	return PreserveStateModifier{}
+// UseStateForUnknown returns a UseStateForUnknownModifier.
+func UseStateForUnknown() AttributePlanModifier {
+	return UseStateForUnknownModifier{}
 }
 
-// PreserveStateModifier is an AttributePlanModifier that copies the prior state
+// UseStateForUnknownModifier is an AttributePlanModifier that copies the prior state
 // value for an attribute into that attribute's plan, if that state is non-null.
 //
-// Computed attributes without the PreserveState attribute plan modifier will
+// Computed attributes without the UseStateForUnknown attribute plan modifier will
 // have their value set to Unknown in the plan, so their value always will be
 // displayed as "(known after apply)" in the CLI plan output.
 // If this plan modifier is used, the prior state value will be displayed in
 // the plan instead unless a prior plan modifier adjusts the value.
-type PreserveStateModifier struct{}
+type UseStateForUnknownModifier struct{}
 
 // Modify copies the attribute's prior state to the attribute plan if the prior
 // state value is not null.
-func (r PreserveStateModifier) Modify(ctx context.Context, req ModifyAttributePlanRequest, resp *ModifyAttributePlanResponse) {
+func (r UseStateForUnknownModifier) Modify(ctx context.Context, req ModifyAttributePlanRequest, resp *ModifyAttributePlanResponse) {
 	if req.AttributeState == nil || resp.AttributePlan == nil || req.AttributeConfig == nil {
 		return
 	}
@@ -189,12 +189,12 @@ func (r PreserveStateModifier) Modify(ctx context.Context, req ModifyAttributePl
 }
 
 // Description returns a human-readable description of the plan modifier.
-func (r PreserveStateModifier) Description(ctx context.Context) string {
+func (r UseStateForUnknownModifier) Description(ctx context.Context) string {
 	return "Once set, the value of this attribute in state will not change."
 }
 
 // MarkdownDescription returns a markdown description of the plan modifier.
-func (r PreserveStateModifier) MarkdownDescription(ctx context.Context) string {
+func (r UseStateForUnknownModifier) MarkdownDescription(ctx context.Context) string {
 	return "Once set, the value of this attribute in state will not change."
 }
 

tfsdk/attribute_plan_modification_test.go

@@ -10,7 +10,7 @@ import (
 	"github.com/hashicorp/terraform-plugin-go/tftypes"
 )
 
-func TestPreserveStateModifier(t *testing.T) {
+func TestUseStateForUnknownModifier(t *testing.T) {
 	t.Parallel()
 
 	type testCase struct {
@@ -148,7 +148,7 @@ func TestPreserveStateModifier(t *testing.T) {
 			resp := &ModifyAttributePlanResponse{
 				AttributePlan: req.AttributePlan,
 			}
-			modifier := PreserveState()
+			modifier := UseStateForUnknown()
 
 			modifier.Modify(context.Background(), req, resp)
 			if resp.Diagnostics.HasError() {