fix: correct handling of func in struct fields (#99)

Wrap functions in struct fields in `reflect.Value` to have a consistent
representation of function inside and outside the interpreter.

Teach assign to wrap a function node if destination is reflect.Value

The same needs to be done for composite literal, in a next commit.

interp/cfg.go

@@ -951,8 +951,14 @@ func (interp *Interpreter) Cfg(root *Node) ([]*Node, error) {
 					n.typ = n.typ.fieldSeq(ti)
 					n.gen = getPtrIndexSeq
 				default:
-					n.typ = n.typ.fieldSeq(ti)
 					n.gen = getIndexSeq
+					n.typ = n.typ.fieldSeq(ti)
+					if n.typ.cat == FuncT {
+						// function in a struct field is always wrapped in reflect.Value
+						rtype := n.typ.TypeOf()
+						n.typ = &Type{cat: ValueT, rtype: rtype}
+						n.fsize = rtype.NumOut()
+					}
 				}
 			} else {
 				err = n.cfgError("undefined selector: %s", n.child[1].ident)

interp/interp_eval_test.go

@@ -1,6 +1,7 @@
 package interp_test
 
 import (
+	"log"
 	"reflect"
 	"testing"
 
@@ -98,6 +99,55 @@ func TestEvalNil2(t *testing.T) {
 	}
 }
 
+func TestEvalStruct0(t *testing.T) {
+	i := interp.New(interp.Opt{})
+	evalCheck(t, i, `
+type Fromage struct {
+	Name string
+	Call func(string) string
+}
+
+func f() string {
+	a := Fromage{}
+	a.Name = "test"
+	a.Call = func(s string) string { return s }
+
+	return a.Call(a.Name)
+}
+`)
+
+	v := evalCheck(t, i, `f()`)
+	if v.Interface().(string) != "test" {
+		t.Fatalf("expected test, got %v", v)
+	}
+}
+
+func TestEvalStruct1(t *testing.T) {
+	t.Skip("not yet implemented")
+	log.SetFlags(log.Lshortfile)
+	i := interp.New(interp.Opt{})
+	evalCheck(t, i, `
+type Fromage struct {
+	Name string
+	Call func(string) string
+}
+
+func f() string {
+	a := Fromage{
+		"test",
+		func(s string) string { return s },
+	}
+
+	return a.Call(a.Name)
+}
+`)
+
+	v := evalCheck(t, i, `f()`)
+	if v.Interface().(string) != "test" {
+		t.Fatalf("expected test, got %v", v)
+	}
+}
+
 func TestEvalComposite0(t *testing.T) {
 	i := interp.New(interp.Opt{})
 	evalCheck(t, i, `

interp/run.go

@@ -192,7 +192,6 @@ func assignX(n *Node) {
 
 // assign implements single value assignment
 func assign(n *Node) {
-	value := genValue(n)
 	next := getExec(n.tnext)
 
 	if n.child[0].typ.cat == InterfaceT {
@@ -203,7 +202,14 @@ func assign(n *Node) {
 			return next
 		}
 	} else {
-		value1 := genValue(n.lastChild())
+		value := genValue(n)
+		dest, src := n.child[0], n.lastChild()
+		var value1 func(*Frame) reflect.Value
+		if dest.typ.cat == ValueT && src.typ.cat == FuncT {
+			value1 = genNodeWrapper(src)
+		} else {
+			value1 = genValue(src)
+		}
 		n.exec = func(f *Frame) Builtin {
 			value(f).Set(value1(f))
 			return next