interp: fix calling of variadic binary methods

Fixes #1046.

interp/interp_export_test.go

@@ -66,3 +66,26 @@ func NewMyInt(i int) wrap.Wrap {
 	w := NewMyInt(4)
 	Hi(w)
 }
+
+type T struct{}
+
+func (t T) Bar(s ...string) {}
+
+func TestCallBinVariadicMethod(t *testing.T) {
+	i := interp.New(interp.Options{})
+	i.Use(interp.Exports{
+		"mypkg/mypkg": {
+			"T": reflect.ValueOf((*T)(nil)),
+		},
+	})
+	eval(t, i, `
+package p
+
+import "mypkg"
+
+func Foo(x mypkg.T) { x.Bar("s") }
+`)
+	v := eval(t, i, "p.Foo")
+	bar := v.Interface().(func(t T))
+	bar(T{})
+}

interp/run.go

@@ -1350,7 +1350,7 @@ func callBin(n *node) {
 
 	for i, c := range child {
 		var defType reflect.Type
-		if variadic >= 0 && i >= variadic {
+		if variadic >= 0 && i+rcvrOffset >= variadic {
 			defType = funcType.In(variadic)
 		} else {
 			defType = funcType.In(rcvrOffset + i)
@@ -1374,7 +1374,7 @@ func callBin(n *node) {
 			if c.kind == basicLit || c.rval.IsValid() {
 				// Convert literal value (untyped) to function argument type (if not an interface{})
 				var argType reflect.Type
-				if variadic >= 0 && i >= variadic {
+				if variadic >= 0 && i+rcvrOffset >= variadic {
 					argType = funcType.In(variadic).Elem()
 				} else {
 					argType = funcType.In(i + rcvrOffset)