fix: PUSH([]T{}) is noop for empty slice (#33)

pushlabels_test.go

@@ -142,6 +142,34 @@ func TestPUSHLabels(t *testing.T) {
 	// t.Logf("want: %d %#x", len(want), want)
 }
 
+func TestPUSHNoLabels(t *testing.T) {
+	// Arbitrary boundaries to surround the empty push; MUST have no effect on
+	// the stack otherwise compilation will fail.
+	const (
+		before = MSIZE
+		after  = GAS
+	)
+
+	code := Code{
+		before,
+		PUSH([]JUMPDEST{}),
+		PUSH([]Label{}),
+		PUSH([]string{}),
+		after,
+	}
+	want := asBytes(before, after)
+
+	t.Logf("%T = {%s, PUSH([]JUMPDEST{}, []Label{}, []string), %s}", code, before, after)
+
+	got, err := code.Compile()
+	if err != nil {
+		t.Fatalf("%T.Compile() error %v", code, err)
+	}
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Errorf("%T.Compile() diff (-want +got):\n%s", code, diff)
+	}
+}
+
 type opCode interface {
 	vm.OpCode | types.OpCode
 }

specops.go

@@ -13,6 +13,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"math/bits"
+	"reflect"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
@@ -87,6 +88,10 @@ func PUSH[P interface {
 ) types.Bytecoder {
 	pToB := types.BytecoderFromStackPusher
 
+	if val := reflect.ValueOf(v); val.Kind() == reflect.Slice && val.Len() == 0 {
+		return Raw{}
+	}
+
 	switch v := any(v).(type) {
 	case int:
 		if v < 0 {