fix: make a copy of defined before detecting recursivness

_test/struct54.go

@@ -0,0 +1,26 @@
+package main
+
+type S struct {
+	t *T
+}
+
+func newS() *S {
+	return &S{
+		t: &T{u: map[string]*U{}},
+	}
+}
+
+type T struct {
+	u map[string]*U
+}
+
+type U struct {
+	a int
+}
+
+func main() {
+	s := newS()
+	_ = s
+
+	println("ok")
+}

interp/type.go

@@ -1260,7 +1260,7 @@ func (t *itype) refType(defined map[string]*itype, wrapRecursive bool) reflect.T
 	if defined[name] != nil && defined[name].rtype != nil {
 		return defined[name].rtype
 	}
-	if t.val != nil && t.val.cat == structT && t.val.rtype == nil && hasRecursiveStruct(t.val, defined) {
+	if t.val != nil && t.val.cat == structT && t.val.rtype == nil && hasRecursiveStruct(t.val, copyDefined(defined)) {
 		// Replace reference to self (direct or indirect) by an interface{} to handle
 		// recursive types with reflect.
 		typ := *t.val
@@ -1367,6 +1367,14 @@ func (t *itype) implements(it *itype) bool {
 	return t.methods().contains(it.methods())
 }
 
+func copyDefined(m map[string]*itype) map[string]*itype {
+	n := make(map[string]*itype, len(m))
+	for k, v := range m {
+		n[k] = v
+	}
+	return n
+}
+
 // hasRecursiveStruct determines if a struct is a recursion or a recursion
 // intermediate. A recursion intermediate is a struct that contains a recursive
 // struct.