fix: compositeSparse handles fields of interface kind

Fixes #776.

_test/issue-776.go

@@ -0,0 +1,39 @@
+package main
+
+import "fmt"
+
+// Filter is a filter
+type Filter interface {
+	Foo()
+}
+
+// GIFT is a gift
+type GIFT struct {
+	Filters []Filter
+}
+
+// New is a new filter list
+func New(filters ...Filter) *GIFT {
+	return &GIFT{
+		Filters: filters,
+	}
+}
+
+// List lists filters
+func (g *GIFT) List() {
+	fmt.Printf("Hello from List!\n")
+}
+
+// MyFilter is one of the filters
+type MyFilter struct{}
+
+// Foo is a foo
+func (f *MyFilter) Foo() {}
+
+func main() {
+	g := New(&MyFilter{})
+	g.List()
+}
+
+// Output:
+// Hello from List!

interp/run.go

@@ -2116,6 +2116,10 @@ func doCompositeSparse(n *node, hasType bool) {
 		switch {
 		case c1.typ.cat == funcT:
 			values[field] = genFunctionWrapper(c1)
+		case c1.typ.cat == interfaceT:
+			values[field] = genValueInterfaceValue(c1)
+		case isArray(c1.typ) && c1.typ.val != nil && c1.typ.val.cat == interfaceT:
+			values[field] = genValueInterfaceArray(c1)
 		case isRecursiveType(n.typ.field[field].typ, n.typ.field[field].typ.rtype):
 			values[field] = genValueRecursiveInterface(c1, n.typ.field[field].typ.rtype)
 		default:

interp/type.go

@@ -1541,6 +1541,10 @@ func isSendChan(t *itype) bool {
 	return rt.Kind() == reflect.Chan && rt.ChanDir() == reflect.SendDir
 }
 func isMap(t *itype) bool { return t.TypeOf().Kind() == reflect.Map }
+func isArray(t *itype) bool {
+	k := t.TypeOf().Kind()
+	return k == reflect.Array || k == reflect.Slice
+}
 
 func isInterfaceSrc(t *itype) bool {
 	return t.cat == interfaceT || (t.cat == aliasT && isInterfaceSrc(t.val))