compiler: reverse args in AppCall

Invoked contract is expecting first argument to be on top of the stack.
Change test to use non-commutative operation to catch this behaviour.

pkg/compiler/codegen.go

@@ -786,6 +786,9 @@ func (c *codegen) convertBuiltin(expr *ast.CallExpr) {
 	case "VerifySignature":
 		emit.Opcode(c.prog.BinWriter, opcode.VERIFY)
 	case "AppCall":
+		numArgs := len(expr.Args) - 1
+		c.emitReverse(numArgs)
+
 		emit.Opcode(c.prog.BinWriter, opcode.APPCALL)
 		buf := c.getByteArray(expr.Args[0])
 		if len(buf) != 20 {

pkg/compiler/interop_test.go

@@ -2,7 +2,6 @@ package compiler_test
 
 import (
 	"fmt"
-	"math/big"
 	"strings"
 	"testing"
 
@@ -55,8 +54,8 @@ func TestFromAddress(t *testing.T) {
 func TestAppCall(t *testing.T) {
 	srcInner := `
 	package foo
-	func Main(a int, b int) int {
+	func Main(a []byte, b []byte) []byte {
-		return a + b
+		return append(a, b...)
 	}
 	`
 
@@ -78,7 +77,7 @@ func TestAppCall(t *testing.T) {
 
 		require.NoError(t, v.Run())
 
-		assertResult(t, v, big.NewInt(42))
+		assertResult(t, v, []byte{1, 2, 3, 4})
 	})
 
 	t.Run("missing script", func(t *testing.T) {
@@ -104,11 +103,11 @@ func TestAppCall(t *testing.T) {
 		package foo
 		import "github.com/CityOfZion/neo-go/pkg/interop/engine"
 		const scriptHash = ` + fmt.Sprintf("%#v", string(ih.BytesBE())) + `
-		func Main() int {
+		func Main() []byte {
-			x := 13
+			x := []byte{1, 2}
-			y := 29
+			y := []byte{3, 4}
 			result := engine.AppCall([]byte(scriptHash), x, y)
-			return result.(int)
+			return result.([]byte)
 		}
 		`
 
@@ -117,7 +116,7 @@ func TestAppCall(t *testing.T) {
 
 		require.NoError(t, v.Run())
 
-		assertResult(t, v, big.NewInt(42))
+		assertResult(t, v, []byte{1, 2, 3, 4})
 	})
 }
 
@@ -125,11 +124,11 @@ func getAppCallScript(h string) string {
 	return `
 	package foo
 	import "github.com/CityOfZion/neo-go/pkg/interop/engine"
-	func Main() int {
+	func Main() []byte {
-		x := 13
+		x := []byte{1, 2}
-		y := 29
+		y := []byte{3, 4}
 		result := engine.AppCall(` + h + `, x, y)
-		return result.(int)
+		return result.([]byte)
 	}
 	`
 }