Add a seqiter_cls gc handler, and a test for these

src/runtime/iterobject.cpp

@@ -58,6 +58,16 @@ Box* seqiterNext(Box* s) {
     return r;
 }
 
+static void seqiterGCVisit(GCVisitor* v, Box* b) {
+    assert(b->cls == seqiter_cls);
+    boxGCHandler(v, b);
+
+    BoxedSeqIter* si = static_cast<BoxedSeqIter*>(b);
+    v->visit(si->b);
+    if (si->next)
+        v->visit(si->next);
+}
+
 static void iterwrapperGCVisit(GCVisitor* v, Box* b) {
     assert(b->cls == iterwrapper_cls);
     boxGCHandler(v, b);
@@ -108,7 +118,7 @@ extern "C" PyObject* PySeqIter_New(PyObject* seq) noexcept {
 }
 
 void setupIter() {
-    seqiter_cls = new BoxedHeapClass(object_cls, NULL, 0, sizeof(BoxedSeqIter), false, "iterator");
+    seqiter_cls = new BoxedHeapClass(object_cls, seqiterGCVisit, 0, sizeof(BoxedSeqIter), false, "iterator");
 
     seqiter_cls->giveAttr("next", new BoxedFunction(boxRTFunction((void*)seqiterNext, UNKNOWN, 1)));
     seqiter_cls->giveAttr("__hasnext__", new BoxedFunction(boxRTFunction((void*)seqiterHasnext, BOXED_BOOL, 1)));

test/tests/iter_gc.py

+# Regression test: make sure we GC special iterator objects correctly
+
+import gc
+
+class C(object):
+    def f(self, i):
+        return i * i
+    def __getitem__(self, i):
+        if i < 1000:
+            return self.f(i)
+        raise IndexError(i)
+
+for i in C():
+    gc.collect()
+    print i
+
+class C2(object):
+    def __init__(self):
+        self.n = 0
+
+    def __iter__(self):
+        return self
+
+    def f(self):
+        self.n += 1
+        return self.n * 2
+    def next(self):
+        if self.n < 1000:
+            return self.f()
+
+        raise StopIteration()
+
+for i in C2():
+    gc.collect()
+    print i