interp: fix handling interface types in wrapped functions

The interpreter interface type was replaced by a reflect.Value in
objects passed or return to function wrappers, losing the ability
to retrieve methods.

The valueInterface is now preserved, and correctly accessed if
wrapped multiple times.

Fixes #977.

_test/interface47.go

@@ -0,0 +1,32 @@
+package main
+
+type Doer interface {
+	Do() error
+}
+
+type T struct {
+	Name string
+}
+
+func (t *T) Do() error { println("in do"); return nil }
+
+func f() (Doer, error) { return &T{"truc"}, nil }
+
+type Ev struct {
+	doer func() (Doer, error)
+}
+
+func (e *Ev) do() {
+	d, _ := e.doer()
+	d.Do()
+}
+
+func main() {
+	e := &Ev{f}
+	println(e != nil)
+	e.do()
+}
+
+// Output:
+// true
+// in do

interp/cfg.go

@@ -1878,8 +1878,15 @@ func compDefineX(sc *scope, n *node) error {
 		if err != nil {
 			return err
 		}
+		for funtype.cat == valueT && funtype.val != nil {
+			// Retrieve original interpreter type from a wrapped function.
+			// Struct fields of function types are always wrapped in valueT to ensure
+			// their possible use in runtime. In that case, the val field retains the
+			// original interpreter type, which is used now.
+			funtype = funtype.val
+		}
 		if funtype.cat == valueT {
-			// Handle functions imported from runtime
+			// Handle functions imported from runtime.
 			for i := 0; i < funtype.rtype.NumOut(); i++ {
 				types = append(types, &itype{cat: valueT, rtype: funtype.rtype.Out(i)})
 			}

interp/run.go

@@ -386,6 +386,7 @@ func typeAssert(n *node, withResult, withOk bool) {
 				}
 				return next
 			}
+			v = valueInterfaceValue(v)
 			ok = canAssertTypes(v.Type(), rtype)
 			if !ok {
 				if !withOk {
@@ -887,11 +888,6 @@ func genFunctionWrapper(n *node) func(*frame) reflect.Value {
 				if v, ok := r.Interface().(*node); ok {
 					result[i] = genFunctionWrapper(v)(f)
 				}
-				if def.typ.ret[i].cat == interfaceT {
-					x := result[i].Interface().(valueInterface).value
-					result[i] = reflect.New(reflect.TypeOf((*interface{})(nil)).Elem()).Elem()
-					result[i].Set(x)
-				}
 			}
 			return result
 		})
@@ -1271,13 +1267,13 @@ func callBin(n *node) {
 			numOut := c.child[0].typ.rtype.NumOut()
 			for j := 0; j < numOut; j++ {
 				ind := c.findex + j
-				values = append(values, func(f *frame) reflect.Value { return f.data[ind] })
+				values = append(values, func(f *frame) reflect.Value { return valueInterfaceValue(f.data[ind]) })
 			}
 		case isRegularCall(c):
 			// Handle nested function calls: pass returned values as arguments
 			for j := range c.child[0].typ.ret {
 				ind := c.findex + j
-				values = append(values, func(f *frame) reflect.Value { return f.data[ind] })
+				values = append(values, func(f *frame) reflect.Value { return valueInterfaceValue(f.data[ind]) })
 			}
 		default:
 			if c.kind == basicLit || c.rval.IsValid() {
@@ -1371,7 +1367,11 @@ func callBin(n *node) {
 			for i := range rvalues {
 				c := n.anc.child[i]
 				if c.ident != "_" {
-					rvalues[i] = genValue(c)
+					if c.typ.cat == interfaceT {
+						rvalues[i] = genValueInterfaceValue(c)
+					} else {
+						rvalues[i] = genValue(c)
+					}
 				}
 			}
 			n.exec = func(f *frame) bltn {
@@ -1714,6 +1714,13 @@ func getMethodByName(n *node) {
 
 	n.exec = func(f *frame) bltn {
 		val := value0(f).Interface().(valueInterface)
+		for {
+			v, ok := val.value.Interface().(valueInterface)
+			if !ok {
+				break
+			}
+			val = v
+		}
 		typ := val.node.typ
 		if typ.node == nil && typ.cat == valueT {
 			// happens with a var of empty interface type, that has value of concrete type

interp/value.go

@@ -297,6 +297,17 @@ func genValueOutput(n *node, t reflect.Type) func(*frame) reflect.Value {
 	return value
 }
 
+func valueInterfaceValue(v reflect.Value) reflect.Value {
+	for {
+		vv, ok := v.Interface().(valueInterface)
+		if !ok {
+			break
+		}
+		v = vv.value
+	}
+	return v
+}
+
 func genValueInterfaceValue(n *node) func(*frame) reflect.Value {
 	value := genValue(n)
 
@@ -307,7 +318,7 @@ func genValueInterfaceValue(n *node) func(*frame) reflect.Value {
 			v.Set(zeroInterfaceValue())
 			v = value(f)
 		}
-		return v.Interface().(valueInterface).value
+		return valueInterfaceValue(v)
 	}
 }