accounts/abi: fix event unpack into slice

+ The event slice unpacker doesn't correctly extract element from the
slice. The indexed arguments are not ignored as they should be
(the data offset should not include the indexed arguments).

+ The `Elem()` call in the slice unpack doesn't work.
The Slice related tests fails because of that.

+ the check in the loop are suboptimal and have been extracted
out of the loop.

+ extracted common code from event and method tupleUnpack

accounts/abi/method.go

@@ -101,7 +101,11 @@ func (method Method) tupleUnpack(v interface{}, output []byte) error {
 	var (
 		value = valueOf.Elem()
 		typ   = value.Type()
+		kind  = value.Kind()
 	)
+	if err := requireUnpackKind(value, typ, kind, method.Outputs, false); err != nil {
+		return err
+	}
 
 	j := 0
 	for i := 0; i < len(method.Outputs); i++ {
@@ -117,7 +121,7 @@ func (method Method) tupleUnpack(v interface{}, output []byte) error {
 		}
 		reflectValue := reflect.ValueOf(marshalledValue)
 
-		switch value.Kind() {
+		switch kind {
 		case reflect.Struct:
 			for j := 0; j < typ.NumField(); j++ {
 				field := typ.Field(j)
@@ -129,19 +133,13 @@ func (method Method) tupleUnpack(v interface{}, output []byte) error {
 				}
 			}
 		case reflect.Slice, reflect.Array:
-			if value.Len() < i {
-				return fmt.Errorf("abi: insufficient number of arguments for unpack, want %d, got %d", len(method.Outputs), value.Len())
-			}
 			v := value.Index(i)
-			if v.Kind() != reflect.Ptr && v.Kind() != reflect.Interface {
-				return fmt.Errorf("abi: cannot unmarshal %v in to %v", v.Type(), reflectValue.Type())
+			if err := requireAssignable(v, reflectValue); err != nil {
+				return err
 			}
-			reflectValue := reflect.ValueOf(marshalledValue)
 			if err := set(v.Elem(), reflectValue, method.Outputs[i]); err != nil {
 				return err
 			}
-		default:
-			return fmt.Errorf("abi: cannot unmarshal tuple in to %v", typ)
 		}
 	}
 	return nil