Do not align by ids for small list and dict objects, which should be aligned by path by first. Otherwise, the build_diff API would return non-empty results on two identical configs. See the added test as an example.

PiperOrigin-RevId: 557540955

Author: panzhufeng

fiddle/_src/diffing.py

@@ -481,9 +481,11 @@ def align_heuristically(old: Any, new: Any, old_name='old', new_name='new'):
   old_by_id = daglish_legacy.collect_value_by_id(old, memoizable_only=True)
   new_by_id = daglish_legacy.collect_value_by_id(new, memoizable_only=True)
   for (value_id, value) in old_by_id.items():
-    if value_id in new_by_id:
-      if alignment.can_align(value, value):
-        alignment.align(value, value)
+    # Do not aligh by id for small container objects.
+    if not _is_small_container(value):
+      if value_id in new_by_id:
+        if alignment.can_align(value, value):
+          alignment.align(value, value)
 
   # Second pass: align any objects that are reachable by the same path.
   path_to_old = daglish_legacy.collect_value_by_path(old, memoizable_only=True)
@@ -504,6 +506,13 @@ def align_heuristically(old: Any, new: Any, old_name='old', new_name='new'):
   return alignment
 
 
+def _is_small_container(value):
+  """Returns if value is a small Sequence or Mapping."""
+  if isinstance(value, (Sequence, Mapping)) and len(repr(value)) < 80:
+    return True
+  return False
+
+
 def _should_align_by_equality(value):
   """Returns true if two equal copies of `value` should be aligned.
 

fiddle/_src/diffing_test.py

@@ -701,6 +701,13 @@ def test_replace_set(self):
                     expected_changes=(diffing.ModifyValue(
                         parse_path('[0]'), set([6])),))
 
+  def test_align_heuristically_identical_configs_w_different_ids(self):
+    a = {'k': [1, 2, 3], 'v': None}
+    b = {'k': [1, 2, 3], 'v': None}
+    x = fdl.Config(make_pair, a, b)
+    y = fdl.Config(make_pair, b, a)
+    self.check_diff(x, y)
+
   def test_root_must_be_aligned(self):
     old = fdl.Config(SimpleClass, 1, 2, 3)
     new = fdl.Config(SimpleClass, 4, 5, 6)