detect cycles in JS Arrays as well

Author: philippedistributive

src/JSArrayProxy.cc

@@ -511,17 +511,26 @@ PyObject *JSArrayProxyMethodDefinitions::JSArrayProxy_richcompare(JSArrayProxy *
 }
 
 PyObject *JSArrayProxyMethodDefinitions::JSArrayProxy_repr(JSArrayProxy *self) {
+  // Detect cyclic objects
+  PyObject *objPtr = PyLong_FromVoidPtr(self->jsArray->get());
+  // For `Py_ReprEnter`, we must get a same PyObject when visiting the same JSObject.
+  // We cannot simply use the object returned by `PyLong_FromVoidPtr` because it won't reuse the PyLongObjects for ints not between -5 and 256.
+  // Instead, we store this PyLongObject in a global dict, using itself as the hashable key, effectively interning the PyLongObject.
+  PyObject *tsDict = PyThreadState_GetDict();
+  PyObject *cyclicKey = PyDict_SetDefault(tsDict, /*key*/ objPtr, /*value*/ objPtr); // cyclicKey = (tsDict[objPtr] ??= objPtr)
+  int i = Py_ReprEnter(cyclicKey);
+  if (i != 0) {
+    return i > 0 ? PyUnicode_FromString("[...]") : NULL;
+  }
+
   Py_ssize_t selfLength = JSArrayProxy_length(self);
 
   if (selfLength == 0) {
+    Py_ReprLeave(cyclicKey);
+    PyDict_DelItem(tsDict, cyclicKey);
     return PyUnicode_FromString("[]");
   }
 
-  Py_ssize_t i = Py_ReprEnter((PyObject *)self);
-  if (i != 0) {
-    return i > 0 ? PyUnicode_FromString("[...]") : NULL;
-  }
-
   _PyUnicodeWriter writer;
 
   _PyUnicodeWriter_Init(&writer);
@@ -569,12 +578,14 @@ PyObject *JSArrayProxyMethodDefinitions::JSArrayProxy_repr(JSArrayProxy *self) {
     goto error;
   }
 
-  Py_ReprLeave((PyObject *)self);
+  Py_ReprLeave(cyclicKey);
+  PyDict_DelItem(tsDict, cyclicKey);
   return _PyUnicodeWriter_Finish(&writer);
 
 error:
   _PyUnicodeWriter_Dealloc(&writer);
-  Py_ReprLeave((PyObject *)self);
+  Py_ReprLeave(cyclicKey);
+  PyDict_DelItem(tsDict, cyclicKey);
   return NULL;
 }