[XLA:Python] Improve error checking for the return value of the to_iterable function of custom pytree nodes.

PiperOrigin-RevId: 617066587

Author: hawkinsp

tests/tree_util_test.py

@@ -17,6 +17,7 @@
 import functools
 import pickle
 import re
+import unittest
 
 from absl.testing import absltest
 from absl.testing import parameterized
@@ -25,6 +26,7 @@
 from jax import tree_util
 from jax import flatten_util
 from jax._src import test_util as jtu
+from jax._src.lib import xla_extension_version
 from jax._src.tree_util import prefix_errors, flatten_one_level
 import jax.numpy as jnp
 
@@ -42,6 +44,19 @@ class ANamedTupleSubclass(ATuple):
 tree_util.register_pytree_node(ATuple2, lambda o: ((o.foo,), o.bar),
                                lambda bar, foo: ATuple2(foo[0], bar))
 
+BadFlattenNonTuple = collections.namedtuple("ATuple2", ("foo", "bar"))
+tree_util.register_pytree_node(BadFlattenNonTuple, lambda o: "hello",
+                               lambda bar, foo: ATuple2(foo[0], bar))
+
+BadFlattenBadArityTuple = collections.namedtuple("ATuple2", ("foo", "bar"))
+tree_util.register_pytree_node(BadFlattenBadArityTuple, lambda o: (2, 3, 4),
+                               lambda bar, foo: ATuple2(foo[0], bar))
+
+BadFlattenNonIterableLeaves = collections.namedtuple("ATuple2", ("foo", "bar"))
+tree_util.register_pytree_node(BadFlattenNonIterableLeaves, lambda o: (7, 7),
+                               lambda bar, foo: ATuple2(foo[0], bar))
+
+
 class AnObject:
 
   def __init__(self, x, y, z):
@@ -762,6 +777,37 @@ def testNamedTupleRegisteredWithoutKeysIsntTreatedAsLeaf(self):
     leaves, _ = tree_util.tree_flatten_with_path(ATuple2(1, 'hi'))
     self.assertLen(leaves, 1)
 
+  @unittest.skipIf(xla_extension_version < 247, "Requires jaxlib>=0.4.26")
+  def testBadFlattenNonTuple(self):
+    t = BadFlattenNonTuple(3, 4)
+    with self.assertRaisesRegex(
+        ValueError,
+        "The to_iterable function for a custom PyTree node should return a"
+        r" \(children, aux_data\) tuple, got 'hello'",
+    ):
+      tree_util.tree_flatten(t)
+
+  @unittest.skipIf(xla_extension_version < 247, "Requires jaxlib>=0.4.26")
+  def testBadFlattenBadArityTuple(self):
+    t = BadFlattenBadArityTuple(3, 4)
+    with self.assertRaisesRegex(
+        ValueError,
+        "The to_iterable function for a custom PyTree node should return a"
+        r" \(children, aux_data\) tuple, got \(2, 3, 4\)",
+    ):
+      tree_util.tree_flatten(t)
+
+  @unittest.skipIf(xla_extension_version < 247, "Requires jaxlib>=0.4.26")
+  def testBadFlattenNonIterableLeaves(self):
+    t = BadFlattenNonIterableLeaves(3, 4)
+    with self.assertRaisesRegex(
+        ValueError,
+        "The to_iterable function for a custom PyTree node should return a"
+        r" \(children, aux_data\) tuple where 'children' is iterable, got "
+        r"\(7, 7\)",
+    ):
+      tree_util.tree_flatten(t)
+
 
 class StaticTest(parameterized.TestCase):