[DRAFT] Implement GenerateResourceConfig RPC and existing Terraform default logic

.changes/unreleased/NOTES-20260304-134617.yaml

@@ -0,0 +1,6 @@
+kind: NOTES
+body: 'This release moves the [resource configuration generation](https://developer.hashicorp.com/terraform/language/import/generating-configuration) logic for the `-generate-config-out` flag from 
+Terraform Core to the SDKv2. There should be no functionality changes for resource configuration generation in this release.'
+time: 2026-03-04T13:46:17.250227-05:00
+custom:
+    Issue: "1559"

go.mod

@@ -16,7 +16,7 @@ require (
 	github.com/hashicorp/logutils v1.0.0
 	github.com/hashicorp/terraform-exec v0.25.0
 	github.com/hashicorp/terraform-json v0.27.2
-	github.com/hashicorp/terraform-plugin-go v0.30.0
+	github.com/hashicorp/terraform-plugin-go v0.30.1-0.20260224203057-7d789423e31f
 	github.com/hashicorp/terraform-plugin-log v0.10.0
 	github.com/mitchellh/copystructure v1.2.0
 	github.com/mitchellh/go-testing-interface v1.14.1

go.sum

@@ -86,6 +86,8 @@ github.com/hashicorp/terraform-json v0.27.2 h1:BwGuzM6iUPqf9JYM/Z4AF1OJ5VVJEEzoK
 github.com/hashicorp/terraform-json v0.27.2/go.mod h1:GzPLJ1PLdUG5xL6xn1OXWIjteQRT2CNT9o/6A9mi9hE=
 github.com/hashicorp/terraform-plugin-go v0.30.0 h1:VmEiD0n/ewxbvV5VI/bYwNtlSEAXtHaZlSnyUUuQK6k=
 github.com/hashicorp/terraform-plugin-go v0.30.0/go.mod h1:8d523ORAW8OHgA9e8JKg0ezL3XUO84H0A25o4NY/jRo=
+github.com/hashicorp/terraform-plugin-go v0.30.1-0.20260224203057-7d789423e31f h1:Gn9urczv0KsRi0YrjI7kdzHNUT2zQ/HLi5lfiLY6oxY=
+github.com/hashicorp/terraform-plugin-go v0.30.1-0.20260224203057-7d789423e31f/go.mod h1:8d523ORAW8OHgA9e8JKg0ezL3XUO84H0A25o4NY/jRo=
 github.com/hashicorp/terraform-plugin-log v0.10.0 h1:eu2kW6/QBVdN4P3Ju2WiB2W3ObjkAsyfBsL3Wh1fj3g=
 github.com/hashicorp/terraform-plugin-log v0.10.0/go.mod h1:/9RR5Cv2aAbrqcTSdNmY1NRHP4E3ekrXRGjqORpXyB0=
 github.com/hashicorp/terraform-registry-address v0.4.0 h1:S1yCGomj30Sao4l5BMPjTGZmCNzuv7/GDTDX99E9gTk=

helper/schema/grpc_provider.go

@@ -76,6 +76,7 @@ func (s *GRPCProviderServer) StopContext(ctx context.Context) context.Context {
 func (s *GRPCProviderServer) serverCapabilities() *tfprotov5.ServerCapabilities {
 	return &tfprotov5.ServerCapabilities{
 		GetProviderSchemaOptional: true,
+		GenerateResourceConfig:    true,
 	}
 }
 
@@ -1785,6 +1786,109 @@ func (s *GRPCProviderServer) ImportResourceState(ctx context.Context, req *tfpro
 	return resp, nil
 }
 
+func (s *GRPCProviderServer) GenerateResourceConfig(ctx context.Context, req *tfprotov5.GenerateResourceConfigRequest) (*tfprotov5.GenerateResourceConfigResponse, error) {
+	ctx = logging.InitContext(ctx)
+
+	resp := &tfprotov5.GenerateResourceConfigResponse{}
+
+	schemaBlock := s.getResourceSchemaBlock(req.TypeName)
+
+	stateVal, err := msgpack.Unmarshal(req.State.MsgPack, schemaBlock.ImpliedType())
+	if err != nil {
+		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, err)
+		return resp, nil
+	}
+
+	if stateVal.IsNull() {
+		resp.Diagnostics = []*tfprotov5.Diagnostic{
+			{
+				Severity: tfprotov5.DiagnosticSeverityError,
+				Summary:  "Unexpected Generate Config Request",
+				Detail: "An unexpected error was encountered when generating resource configuration. The current state was missing.\n\n" +
+					"This is always a problem with Terraform or terraform-plugin-sdk. Please report this to the provider developer.",
+			},
+		}
+
+	}
+
+	newConfigVal := stateVal
+
+	// Handle top level attributes and defaults
+	newConfigVal, err = cty.Transform(newConfigVal, func(path cty.Path, val cty.Value) (cty.Value, error) {
+		if val.IsNull() {
+			return val, nil
+		}
+
+		if len(path) == 0 {
+			return val, nil
+		}
+
+		ty := val.Type()
+		null := cty.NullVal(ty)
+
+		// find the attribute or block schema representing the value
+		attr := schemaBlock.AttributeByPath(path)
+		block := schemaBlock.BlockByPath(path)
+		switch {
+		case attr != nil:
+			// deprecated attributes
+			if attr.Deprecated {
+				return null, nil
+			}
+
+			// read-only attributes are not written in the configuration
+			if attr.Computed && !attr.Optional {
+				return null, nil
+			}
+
+			// The legacy SDK adds an Optional+Computed "id" attribute to the
+			// resource schema even if not defined in provider code.
+			// During validation, however, the presence of an extraneous "id"
+			// attribute in config will cause an error.
+			// Remove this attribute so we do not generate an "id" attribute
+			// where there is a risk that it is not in the real resource schema.
+			if path.Equals(cty.GetAttrPath("id")) && attr.Computed && attr.Optional {
+				return null, nil
+			}
+
+			// If we have "" for an optional value, assume it is actually null
+			// due to the legacy SDK.
+			if ty == cty.String {
+				if !val.IsNull() && attr.Optional && len(val.AsString()) == 0 {
+					return null, nil
+				}
+			}
+			return val, nil
+
+		case block != nil:
+			if block.Deprecated {
+				return null, nil
+			}
+		}
+
+		return val, nil
+	})
+	if err != nil {
+		configErr := fmt.Errorf("An unexpected error occurred while trying to generate resource configuration. "+
+			"This is an error in terraform-plugin-sdk used by the provider. "+
+			"Please report the following to the provider developers.\n\n"+
+			"Original Error: %s", err.Error())
+		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, configErr)
+		return resp, nil
+	}
+
+	newConfigMP, err := msgpack.Marshal(newConfigVal, schemaBlock.ImpliedType())
+	if err != nil {
+		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, err)
+		return resp, nil
+	}
+	resp.Config = &tfprotov5.DynamicValue{
+		MsgPack: newConfigMP,
+	}
+
+	return resp, nil
+}
+
 func (s *GRPCProviderServer) MoveResourceState(ctx context.Context, req *tfprotov5.MoveResourceStateRequest) (*tfprotov5.MoveResourceStateResponse, error) {
 	if req == nil {
 		return nil, fmt.Errorf("MoveResourceState request is nil")