feat: Add support for named types with underlying basic types

rlp/rlpgen/gen.go

@@ -373,6 +373,29 @@ func (op uint256Op) genDecode(ctx *genContext) (string, string) {
 	return result, b.String()
 }
 
+func (bctx *buildContext) makeNamedBasicOp(named *types.Named) (op, error) {
+	underlying := named.Underlying()
+	basic, ok := underlying.(*types.Basic)
+	if !ok {
+		return nil, fmt.Errorf("expected basic type, got %T", underlying)
+	}
+
+	// Use the existing makeBasicOp function to get the base operation
+	baseOp, err := bctx.makeBasicOp(basic)
+	if err != nil {
+		return nil, err
+	}
+
+	// Cast to basicOp and modify the typ field to use the named type
+	op, ok := baseOp.(basicOp)
+	if !ok {
+		return nil, fmt.Errorf("expected basicOp, got %T", baseOp)
+	}
+	op.typ = named // Use the named type as the main type instead of the underlying basic type
+
+	return op, nil
+}
+
 // encoderDecoderOp handles rlp.Encoder and rlp.Decoder.
 // In order to be used with this, the type must implement both interfaces.
 // This restriction may be lifted in the future by creating separate ops for
@@ -684,6 +707,9 @@ func (bctx *buildContext) makeOp(name *types.Named, typ types.Type, tags rlpstru
 		if typ == bctx.rawValueType {
 			return bctx.makeRawValueOp(), nil
 		}
+		if isNamedWithBasicUnderlying(typ) {
+			return bctx.makeNamedBasicOp(typ)
+		}
 		if bctx.isDecoder(typ) {
 			return nil, fmt.Errorf("type %v implements rlp.Decoder with non-pointer receiver", typ)
 		}

rlp/rlpgen/gen_test.go

@@ -47,7 +47,7 @@ func init() {
 	}
 }
 
-var tests = []string{"uints", "nil", "rawvalue", "optional", "bigint", "uint256", "alias"}
+var tests = []string{"uints", "nil", "rawvalue", "optional", "bigint", "uint256", "alias", "named"}
 
 func TestOutput(t *testing.T) {
 	for _, test := range tests {
@@ -66,7 +66,7 @@ func TestOutput(t *testing.T) {
 
 			// Set this environment variable to regenerate the test outputs.
 			if os.Getenv("WRITE_TEST_FILES") != "" {
-				os.WriteFile(outputFile, output, 0644)
+				os.WriteFile(outputFile, output, 0o644)
 			}
 
 			// Check if output matches.

rlp/rlpgen/testdata/named.in.txt

@@ -0,0 +1,15 @@
+// -*- mode: go -*-
+
+package test
+
+type (
+    BoolT   bool
+    Uint64T uint64
+    StringT string
+)
+
+type Test struct {
+    BoolNewT BoolT
+    Uint64NewT Uint64T
+    StringNewT StringT
+}

rlp/rlpgen/testdata/named.out.txt

@@ -0,0 +1,49 @@
+package test
+
+import "github.com/ava-labs/libevm/rlp"
+import "io"
+
+func (obj *Test) EncodeRLP(_w io.Writer) error {
+	w := rlp.NewEncoderBuffer(_w)
+	_tmp0 := w.List()
+	w.WriteBool(bool(obj.BoolNewT))
+	w.WriteUint64(uint64(obj.Uint64NewT))
+	w.WriteString(string(obj.StringNewT))
+	w.ListEnd(_tmp0)
+	return w.Flush()
+}
+
+func (obj *Test) DecodeRLP(dec *rlp.Stream) error {
+	var _tmp0 Test
+	{
+		if _, err := dec.List(); err != nil {
+			return err
+		}
+		// BoolNewT:
+		_tmp1, err := dec.Bool()
+		if err != nil {
+			return err
+		}
+		_tmp2 := BoolT(_tmp1)
+		_tmp0.BoolNewT = _tmp2
+		// Uint64NewT:
+		_tmp3, err := dec.Uint64()
+		if err != nil {
+			return err
+		}
+		_tmp4 := Uint64T(_tmp3)
+		_tmp0.Uint64NewT = _tmp4
+		// StringNewT:
+		_tmp5, err := dec.String()
+		if err != nil {
+			return err
+		}
+		_tmp6 := StringT(_tmp5)
+		_tmp0.StringNewT = _tmp6
+		if err := dec.ListEnd(); err != nil {
+			return err
+		}
+	}
+	*obj = _tmp0
+	return nil
+}

rlp/rlpgen/types.go

@@ -113,6 +113,16 @@ func isByte(typ types.Type) bool {
 	return ok && basic.Kind() == types.Uint8
 }
 
+// isNamedWithBasicUnderlying checks whether 'typ' is a named type with an underlying basic type.
+func isNamedWithBasicUnderlying(typ types.Type) bool {
+	named, ok := typ.(*types.Named)
+	if !ok {
+		return false
+	}
+	_, ok = named.Underlying().(*types.Basic)
+	return ok
+}
+
 func resolveUnderlying(typ types.Type) types.Type {
 	for {
 		t := typ.Underlying()