internal/fwserver: Ensure computed dynamic values are marked as dynam…

…ic type during plan modification (#970)

* internal/fwserver: Ensure computed dynamic values are marked as dynamic type during plan modification

* Update .changes/unreleased/BUG FIXES-20240325-101108.yaml

Co-authored-by: Brian Flad <bflad417@gmail.com>

---------

Co-authored-by: Brian Flad <bflad417@gmail.com>

.changes/unreleased/BUG FIXES-20240325-101108.yaml

@@ -0,0 +1,6 @@
+kind: BUG FIXES
+body: 'resource: Ensured computed-only dynamic attributes will not cause `wrong final
+  value type` errors during planning'
+time: 2024-03-25T10:11:08.813527-04:00
+custom:
+  Issue: "969"

internal/fwserver/server_planresourcechange.go

@@ -20,6 +20,7 @@ import (
 	"github.com/hashicorp/terraform-plugin-framework/path"
 	"github.com/hashicorp/terraform-plugin-framework/resource"
 	"github.com/hashicorp/terraform-plugin-framework/tfsdk"
+	"github.com/hashicorp/terraform-plugin-framework/types/basetypes"
 )
 
 // PlanResourceChangeRequest is the framework server request for the
@@ -406,9 +407,19 @@ func MarkComputedNilsAsUnknown(ctx context.Context, config tftypes.Value, resour
 			}
 		}
 
+		// Value type from planned state to create unknown with
+		newValueType := val.Type()
+
+		// If the attribute is dynamic then we can't use the planned state value to create an unknown, as it may be a concrete type.
+		// This logic explicitly sets the unknown value type to dynamic so the type can be determined during apply.
+		_, isDynamic := attribute.GetType().(basetypes.DynamicTypable)
+		if isDynamic {
+			newValueType = tftypes.DynamicPseudoType
+		}
+
 		logging.FrameworkDebug(ctx, "marking computed attribute that is null in the config as unknown")
 
-		return tftypes.NewValue(val.Type(), tftypes.UnknownValue), nil
+		return tftypes.NewValue(newValueType, tftypes.UnknownValue), nil
 	}
 }
 

internal/fwserver/server_planresourcechange_test.go

@@ -78,7 +78,7 @@ func TestMarkComputedNilsAsUnknown(t *testing.T) {
 			"dynamic-nil-computed": schema.DynamicAttribute{
 				Computed: true,
 			},
-			// underlying nil computed values should be turned into unknown, preserving the original type
+			// underlying nil computed values should be turned into unknown, this should not preserve the original type
 			"dynamic-underlying-string-nil-computed": schema.DynamicAttribute{
 				Computed: true,
 			},
@@ -274,7 +274,7 @@ func TestMarkComputedNilsAsUnknown(t *testing.T) {
 		"dynamic-value":                          tftypes.NewValue(tftypes.String, "hello, world"),
 		"dynamic-nil":                            tftypes.NewValue(tftypes.DynamicPseudoType, nil),
 		"dynamic-nil-computed":                   tftypes.NewValue(tftypes.DynamicPseudoType, tftypes.UnknownValue),
-		"dynamic-underlying-string-nil-computed": tftypes.NewValue(tftypes.String, tftypes.UnknownValue), // Preserves the underlying string type
+		"dynamic-underlying-string-nil-computed": tftypes.NewValue(tftypes.DynamicPseudoType, tftypes.UnknownValue), // doesn't preserve original type
 		"dynamic-nil-optional-computed":          tftypes.NewValue(tftypes.DynamicPseudoType, tftypes.UnknownValue),
 		"dynamic-value-optional-computed":        tftypes.NewValue(tftypes.String, "hello, world"),
 		"dynamic-value-with-underlying-list-optional-computed": tftypes.NewValue(