internal/privatestate: Handle terraform-plugin-sdk private state in NewData

.changelog/452.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+resource: Prevented `Error Decoding Private State` errors on resources previously managed by terraform-plugin-sdk
+```

internal/privatestate/data.go

@@ -10,6 +10,7 @@ import (
 	"github.com/hashicorp/terraform-plugin-log/tflog"
 
 	"github.com/hashicorp/terraform-plugin-framework/diag"
+	"github.com/hashicorp/terraform-plugin-framework/internal/logging"
 )
 
 // Data contains private state data for the framework and providers.
@@ -113,6 +114,20 @@ func NewData(ctx context.Context, data []byte) (*Data, diag.Diagnostics) {
 
 	err := json.Unmarshal(data, &dataMap)
 	if err != nil {
+		// terraform-plugin-sdk stored private state by marshalling its data
+		// as map[string]any, which is slightly incompatible with trying to
+		// unmarshal it as map[string][]byte. If unmarshalling with
+		// map[string]any works, we can ignore it for now, as provider
+		// developers did not have access to managing the private state data.
+		//
+		// TODO: We can extract the terraform-plugin-sdk resource timeouts key
+		// here to extract its prior data, if necessary.
+		// Reference: https://github.com/hashicorp/terraform-plugin-framework/issues/400
+		if anyErr := json.Unmarshal(data, new(map[string]any)); anyErr == nil {
+			logging.FrameworkWarn(ctx, "Discarding incompatible resource private state data", map[string]any{logging.KeyError: err.Error()})
+			return nil, nil
+		}
+
 		diags.AddError(
 			"Error Decoding Private State",
 			fmt.Sprintf("An error was encountered when decoding private state: %s.\n\n"+

internal/privatestate/data_test.go

@@ -2,6 +2,7 @@ package privatestate
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"testing"
 
@@ -281,6 +282,14 @@ func TestNewData(t *testing.T) {
 		"providerKeyTwo":   []byte(`{"pKeyTwo": {"k2": "two", "k3": 3}}`),
 	})
 
+	sdkJSON, err := json.Marshal(map[string]any{
+		"schema_version": "2",
+	})
+
+	if err != nil {
+		t.Fatalf("unexpected error marshaling SDK JSON: %s", err)
+	}
+
 	testCases := map[string]struct {
 		data          []byte
 		expected      *Data
@@ -410,6 +419,10 @@ func TestNewData(t *testing.T) {
 				},
 			},
 		},
+		"sdk-ignore": {
+			data:     sdkJSON,
+			expected: nil,
+		},
 	}
 
 	for name, testCase := range testCases {