vm: implement Array <-> Struct conversion

Reference VM implementation supports convertation from
Struct to Array via NEWARRAY and vice versa.
https://github.com/neo-project/neo-vm/pull/91

pkg/vm/vm.go

@@ -569,14 +569,34 @@ func (v *VM) execute(ctx *Context, op Instruction) {
 
 	// Object operations.
 	case NEWARRAY:
-		n := v.estack.Pop().BigInt().Int64()
-		items := make([]StackItem, n)
-		v.estack.PushVal(&ArrayItem{items})
+		item := v.estack.Pop()
+		switch t := item.value.(type) {
+		case *BigIntegerItem:
+			n := t.value.Int64()
+			items := make([]StackItem, n)
+			v.estack.PushVal(&ArrayItem{items})
+		case *StructItem:
+			v.estack.PushVal(&ArrayItem{t.value})
+		case *ArrayItem:
+			v.estack.PushVal(t)
+		default:
+			panic("NEWARRAY: invalid operand")
+		}
 
 	case NEWSTRUCT:
-		n := v.estack.Pop().BigInt().Int64()
-		items := make([]StackItem, n)
-		v.estack.PushVal(&StructItem{items})
+		item := v.estack.Pop()
+		switch t := item.value.(type) {
+		case *BigIntegerItem:
+			n := t.value.Int64()
+			items := make([]StackItem, n)
+			v.estack.PushVal(&StructItem{items})
+		case *ArrayItem:
+			v.estack.PushVal(&StructItem{t.value})
+		case *StructItem:
+			v.estack.PushVal(t)
+		default:
+			panic("NEWSTRUCT: invalid operand")
+		}
 
 	case APPEND:
 		itemElem := v.estack.Pop()

pkg/vm/vm_test.go

@@ -216,6 +216,86 @@ func TestINC(t *testing.T) {
 	assert.Equal(t, big.NewInt(2), vm.estack.Pop().BigInt())
 }
 
+func TestNEWARRAYInteger(t *testing.T) {
+	prog := makeProgram(NEWARRAY)
+	vm := load(prog)
+	vm.estack.PushVal(1)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, &ArrayItem{make([]StackItem, 1)}, vm.estack.Pop().value)
+}
+
+func TestNEWARRAYStruct(t *testing.T) {
+	prog := makeProgram(NEWARRAY)
+	vm := load(prog)
+	arr := []StackItem{makeStackItem(42)}
+	vm.estack.Push(&Element{value: &StructItem{arr}})
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, &ArrayItem{arr}, vm.estack.Pop().value)
+}
+
+func TestNEWARRAYArray(t *testing.T) {
+	prog := makeProgram(NEWARRAY)
+	vm := load(prog)
+	arr := []StackItem{makeStackItem(42)}
+	vm.estack.Push(&Element{value: &ArrayItem{arr}})
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, &ArrayItem{arr}, vm.estack.Pop().value)
+}
+
+func TestNEWARRAYWrongType(t *testing.T) {
+	prog := makeProgram(NEWARRAY)
+	vm := load(prog)
+	vm.estack.Push(NewElement([]byte{}))
+	vm.Run()
+	assert.Equal(t, true, vm.state.HasFlag(faultState))
+}
+
+func TestNEWSTRUCTInteger(t *testing.T) {
+	prog := makeProgram(NEWSTRUCT)
+	vm := load(prog)
+	vm.estack.PushVal(1)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, &StructItem{make([]StackItem, 1)}, vm.estack.Pop().value)
+}
+
+func TestNEWSTRUCTArray(t *testing.T) {
+	prog := makeProgram(NEWSTRUCT)
+	vm := load(prog)
+	arr := []StackItem{makeStackItem(42)}
+	vm.estack.Push(&Element{value: &ArrayItem{arr}})
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, &StructItem{arr}, vm.estack.Pop().value)
+}
+
+func TestNEWSTRUCTStruct(t *testing.T) {
+	prog := makeProgram(NEWSTRUCT)
+	vm := load(prog)
+	arr := []StackItem{makeStackItem(42)}
+	vm.estack.Push(&Element{value: &StructItem{arr}})
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, &StructItem{arr}, vm.estack.Pop().value)
+}
+
+func TestNEWSTRUCTWrongType(t *testing.T) {
+	prog := makeProgram(NEWSTRUCT)
+	vm := load(prog)
+	vm.estack.Push(NewElement([]byte{}))
+	vm.Run()
+	assert.Equal(t, true, vm.state.HasFlag(faultState))
+}
+
 func TestAppCall(t *testing.T) {
 	prog := []byte{byte(APPCALL)}
 	hash := util.Uint160{}