Support simple generic types

.gitignore

@@ -1,2 +1,3 @@
 eth2.0-spec-tests
-*.tar.gz
+*.tar.gz
+.idea

sszgen/generator/generator.go

@@ -518,12 +518,13 @@ func appendObjSignature(str string, v *Value) string {
 }
 
 type astStruct struct {
-	name     string
-	obj      *ast.StructType
-	packName string
-	typ      ast.Expr
-	implFunc bool
-	isRef    bool
+	name       string
+	obj        *ast.StructType
+	packName   string
+	typ        ast.Expr
+	implFunc   bool
+	isRef      bool
+	paramTypes map[string]int
 }
 
 func (a *astStruct) isAlias() bool {
@@ -565,6 +566,14 @@ func decodeASTStruct(file *ast.File) *astResult {
 					if ok {
 						// type is a struct
 						obj.obj = structType
+
+						// process the type params if there is any
+						if typeSpec.TypeParams != nil && len(typeSpec.TypeParams.List) > 0 {
+							obj.paramTypes = map[string]int{}
+							for i, typ := range typeSpec.TypeParams.List {
+								obj.paramTypes[typ.Names[0].Name] = i
+							}
+						}
 					} else {
 						if _, ok := typeSpec.Type.(*ast.InterfaceType); !ok {
 							// type is an alias (skip interfaces)
@@ -922,8 +931,8 @@ func (e *env) parseASTStructType(name string) (*Value, error) {
 
 	visited := map[string]struct{}{}
 
-	var getFields func(subName string) ([]*ast.Field, error)
-	getFields = func(subName string) ([]*ast.Field, error) {
+	var getFields func(subName string, genericTypes []string) ([]*ast.Field, error)
+	getFields = func(subName string, genericTypes []string) ([]*ast.Field, error) {
 		if _, ok := visited[subName]; ok {
 			return nil, fmt.Errorf("loop in embed types %s", subName)
 		}
@@ -946,24 +955,57 @@ func (e *env) parseASTStructType(name string) (*Value, error) {
 					// skip protobuf methods
 					continue
 				}
+				if itype, ok := f.Type.(*ast.Ident); ok {
+					if genericIndex, ok := item.paramTypes[itype.Name]; ok {
+						f.Type.(*ast.Ident).Name = genericTypes[genericIndex]
+					}
+				}
+
 				fields = append(fields, f)
 			} else if len(f.Names) == 0 {
-				// embed item in the same package, resolve it recursively
-				ident, ok := f.Type.(*ast.Ident)
-				if !ok {
-					return nil, fmt.Errorf("embed type expects a typed object in same package but %s found", reflect.TypeOf(f.Type))
-				}
-				subFields, err := getFields(ident.Name)
-				if err != nil {
-					return nil, err
+				switch tp := f.Type.(type) {
+				case *ast.Ident:
+					// embed item in the same package, resolve it recursively
+					subFields, err := getFields(tp.Name, nil)
+					if err != nil {
+						return nil, err
+					}
+					fields = append(fields, subFields...)
+				case *ast.IndexExpr:
+					// embed item is a generic type with one parameter
+					genericType, ok := tp.Index.(*ast.Ident)
+					if !ok {
+						return nil, fmt.Errorf("embed type expects a typed object but %s found", reflect.TypeOf(tp.Index))
+					}
+					subFields, err := getFields(tp.X.(*ast.Ident).Name, []string{genericType.Name})
+					if err != nil {
+						return nil, err
+					}
+					fields = append(fields, subFields...)
+				case *ast.IndexListExpr:
+					// embed item is a generic type with two or more parameters
+					var typeList []string
+					for _, index := range tp.Indices {
+						genericType, ok := index.(*ast.Ident)
+						if !ok {
+							return nil, fmt.Errorf("embed type expects a typed object but %s found", reflect.TypeOf(index))
+						}
+						typeList = append(typeList, genericType.Name)
+					}
+					subFields, err := getFields(tp.X.(*ast.Ident).Name, typeList)
+					if err != nil {
+						return nil, err
+					}
+					fields = append(fields, subFields...)
+				default:
+					return nil, fmt.Errorf("unknwon embed type %s found", reflect.TypeOf(f.Type))
 				}
-				fields = append(fields, subFields...)
 			}
 		}
 		return fields, nil
 	}
 
-	fields, err := getFields(name)
+	fields, err := getFields(name, nil)
 	if err != nil {
 		return nil, err
 	}

sszgen/testcases/generics.go

@@ -0,0 +1,28 @@
+package testcases
+
+//go:generate go run ../main.go --path generics.go --objs Test1,Test2
+
+type Generic[T comparable] struct {
+	Value T
+}
+
+type Wrapper struct {
+	Generic[uint64]
+}
+
+type Test1 struct {
+	G Wrapper
+}
+
+type Generic2[T any, F any] struct {
+	Value1 T
+	Value2 F
+}
+
+type Wrapper2 struct {
+	Generic2[uint64, uint16]
+}
+
+type Test2 struct {
+	G Wrapper2
+}