gh-130851: Only intern constants of types generated by the compiler (#130901)

The free-threading build interns and immortalizes most constants
generated by the bytecode compiler. However, users can construct their
own code objects with arbitrary constants. We should not intern or
immortalize these objects if they are not of a type that we know how to
handle.

This change fixes a reference leak failure in the recently added
`test_code.test_unusual_constants` test. It also addresses a potential
crash that could occur when attempting to destroy an immortalized
object during interpreter shutdown.

Author: colesbury

Objects/codeobject.c

@@ -135,6 +135,44 @@ should_intern_string(PyObject *o)
 
 #ifdef Py_GIL_DISABLED
 static PyObject *intern_one_constant(PyObject *op);
+
+// gh-130851: In the free threading build, we intern and immortalize most
+// constants, except code objects. However, users can generate code objects
+// with arbitrary co_consts. We don't want to immortalize or intern unexpected
+// constants or tuples/sets containing unexpected constants.
+static int
+should_immortalize_constant(PyObject *v)
+{
+    // Only immortalize containers if we've already immortalized all their
+    // elements.
+    if (PyTuple_CheckExact(v)) {
+        for (Py_ssize_t i = PyTuple_GET_SIZE(v); --i >= 0; ) {
+            if (!_Py_IsImmortal(PyTuple_GET_ITEM(v, i))) {
+                return 0;
+            }
+        }
+        return 1;
+    }
+    else if (PyFrozenSet_CheckExact(v)) {
+        PyObject *item;
+        Py_hash_t hash;
+        Py_ssize_t pos = 0;
+        while (_PySet_NextEntry(v, &pos, &item, &hash)) {
+            if (!_Py_IsImmortal(item)) {
+                return 0;
+            }
+        }
+        return 1;
+    }
+    else if (PySlice_Check(v)) {
+        PySliceObject *slice = (PySliceObject *)v;
+        return (_Py_IsImmortal(slice->start) &&
+                _Py_IsImmortal(slice->stop) &&
+                _Py_IsImmortal(slice->step));
+    }
+    return (PyLong_CheckExact(v) || PyFloat_CheckExact(v) ||
+            PyComplex_Check(v) || PyBytes_CheckExact(v));
+}
 #endif
 
 static int
@@ -241,8 +279,9 @@ intern_constants(PyObject *tuple, int *modified)
 
         // Intern non-string constants in the free-threaded build
         _PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
-        if (!_Py_IsImmortal(v) && !PyCode_Check(v) &&
-            !PyUnicode_CheckExact(v) && !tstate->suppress_co_const_immortalization)
+        if (!_Py_IsImmortal(v) && !PyUnicode_CheckExact(v) &&
+            should_immortalize_constant(v) &&
+            !tstate->suppress_co_const_immortalization)
         {
             PyObject *interned = intern_one_constant(v);
             if (interned == NULL) {