gh-130851: Don't crash when deduping unusual code constants (#130853)

The bytecode compiler only generates a few different types of constants,
like str, int, tuple, slices, etc. Users can construct code objects with
various unusual constants, including ones that are not hashable or not
even constant.

The free threaded build previously crashed with a fatal error when
confronted with these constants. Instead, treat distinct objects of
otherwise unhandled types as not equal for the purposes of deduplication.

Lib/test/test_code.py

@@ -665,6 +665,23 @@ class CodeConstsTest(unittest.TestCase):
 
         self.assertTrue(globals["func1"]() is globals["func2"]())
 
+    @cpython_only
+    def test_unusual_constants(self):
+        # gh-130851: Code objects constructed with constants that are not
+        # types generated by the bytecode compiler should not crash the
+        # interpreter.
+        class Unhashable:
+            def __hash__(self):
+                raise TypeError("unhashable type")
+
+        class MyInt(int):
+            pass
+
+        code = compile("a = 1", "<string>", "exec")
+        code = code.replace(co_consts=(1, Unhashable(), MyInt(1), MyInt(1)))
+        self.assertIsInstance(code.co_consts[1], Unhashable)
+        self.assertEqual(code.co_consts[2], code.co_consts[3])
+
 
 class CodeWeakRefTest(unittest.TestCase):
 

Misc/NEWS.d/next/Core_and_Builtins/2025-03-04-20-33-28.gh-issue-130851.MT9j7n.rst

@@ -0,0 +1,3 @@
+Fix a crash in the :term:`free threading` build when constructing a
+:class:`code` object with :attr:`~codeobject.co_consts` that contains instances
+of types that are not otherwise generated by the bytecode compiler.

Objects/codeobject.c

@@ -2587,6 +2587,7 @@ intern_one_constant(PyObject *op)
     _Py_hashtable_entry_t *entry = _Py_hashtable_get_entry(consts, op);
     if (entry == NULL) {
         if (_Py_hashtable_set(consts, op, op) != 0) {
+            PyErr_NoMemory();
             return NULL;
         }
 
@@ -2608,7 +2609,8 @@ intern_one_constant(PyObject *op)
 }
 
 static int
-compare_constants(const void *key1, const void *key2) {
+compare_constants(const void *key1, const void *key2)
+{
     PyObject *op1 = (PyObject *)key1;
     PyObject *op2 = (PyObject *)key2;
     if (op1 == op2) {
@@ -2668,8 +2670,8 @@ compare_constants(const void *key1, const void *key2) {
         Py_complex c2 = ((PyComplexObject *)op2)->cval;
         return memcmp(&c1, &c2, sizeof(Py_complex)) == 0;
     }
-    _Py_FatalErrorFormat("unexpected type in compare_constants: %s",
-                         Py_TYPE(op1)->tp_name);
+    // gh-130851: Treat instances of unexpected types as distinct if they are
+    // not the same object.
     return 0;
 }
 
@@ -2689,9 +2691,13 @@ hash_const(const void *key)
     }
     Py_hash_t h = PyObject_Hash(op);
     if (h == -1) {
-        // This should never happen: all the constants we support have
-        // infallible hash functions.
-        Py_FatalError("code: hash failed");
+        // gh-130851: Other than slice objects, every constant that the
+        // bytecode compiler generates is hashable. However, users can
+        // provide their own constants, when constructing code objects via
+        // types.CodeType(). If the user-provided constant is unhashable, we
+        // use the memory address of the object as a fallback hash value.
+        PyErr_Clear();
+        return (Py_uhash_t)(uintptr_t)key;
     }
     return (Py_uhash_t)h;
 }