[DRAFT] Implement GenerateResourceConfig RPC and existing Terraform default logic

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/resource/testcase_providers.go

@@ -20,26 +20,26 @@ func (c TestCase) providerConfig(_ context.Context, skipProviderBlock bool) stri
 	//      is being used and not the others, but leaving it here just in case
 	//      it does have a special purpose that wasn't being unit tested prior.
 	for name := range c.Providers {
-		providerBlocks.WriteString(fmt.Sprintf("provider %q {}\n", name))
+		fmt.Fprintf(&providerBlocks, "provider %q {}\n", name)
 	}
 
 	for name, externalProvider := range c.ExternalProviders {
 		if !skipProviderBlock {
-			providerBlocks.WriteString(fmt.Sprintf("provider %q {}\n", name))
+			fmt.Fprintf(&providerBlocks, "provider %q {}\n", name)
 		}
 
 		if externalProvider.Source == "" && externalProvider.VersionConstraint == "" {
 			continue
 		}
 
-		requiredProviderBlocks.WriteString(fmt.Sprintf("    %s = {\n", name))
+		fmt.Fprintf(&requiredProviderBlocks, "    %s = {\n", name)
 
 		if externalProvider.Source != "" {
-			requiredProviderBlocks.WriteString(fmt.Sprintf("      source = %q\n", externalProvider.Source))
+			fmt.Fprintf(&requiredProviderBlocks, "      source = %q\n", externalProvider.Source)
 		}
 
 		if externalProvider.VersionConstraint != "" {
-			requiredProviderBlocks.WriteString(fmt.Sprintf("      version = %q\n", externalProvider.VersionConstraint))
+			fmt.Fprintf(&requiredProviderBlocks, "      version = %q\n", externalProvider.VersionConstraint)
 		}
 
 		requiredProviderBlocks.WriteString("    }\n")

helper/resource/teststep_providers.go

@@ -61,21 +61,21 @@ func (s TestStep) providerConfig(_ context.Context, skipProviderBlock bool) stri
 
 	for name, externalProvider := range s.ExternalProviders {
 		if !skipProviderBlock {
-			providerBlocks.WriteString(fmt.Sprintf("provider %q {}\n", name))
+			fmt.Fprintf(&providerBlocks, "provider %q {}\n", name)
 		}
 
 		if externalProvider.Source == "" && externalProvider.VersionConstraint == "" {
 			continue
 		}
 
-		requiredProviderBlocks.WriteString(fmt.Sprintf("    %s = {\n", name))
+		fmt.Fprintf(&requiredProviderBlocks, "    %s = {\n", name)
 
 		if externalProvider.Source != "" {
-			requiredProviderBlocks.WriteString(fmt.Sprintf("      source = %q\n", externalProvider.Source))
+			fmt.Fprintf(&requiredProviderBlocks, "      source = %q\n", externalProvider.Source)
 		}
 
 		if externalProvider.VersionConstraint != "" {
-			requiredProviderBlocks.WriteString(fmt.Sprintf("      version = %q\n", externalProvider.VersionConstraint))
+			fmt.Fprintf(&requiredProviderBlocks, "      version = %q\n", externalProvider.VersionConstraint)
 		}
 
 		requiredProviderBlocks.WriteString("    }\n")

helper/schema/field_reader_config_test.go

@@ -461,8 +461,8 @@ func TestConfigFieldReader_computedComplexSet(t *testing.T) {
 	hashfunc := func(v interface{}) int {
 		var buf bytes.Buffer
 		m := v.(map[string]interface{})
-		buf.WriteString(fmt.Sprintf("%s-", m["name"].(string)))
-		buf.WriteString(fmt.Sprintf("%s-", m["vhd_uri"].(string)))
+		fmt.Fprintf(&buf, "%s-", m["name"].(string))
+		fmt.Fprintf(&buf, "%s-", m["vhd_uri"].(string))
 		return hashcode.String(buf.String())
 	}
 

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 +1786,93 @@ 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
+	}
+
+	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 {
+		resp.Diagnostics = convert.AppendProtoDiag(ctx, resp.Diagnostics, err)
+		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")