fix: withdrawn by author

lms/djangoapps/course_blocks/transformers/library_content.py

@@ -112,7 +112,11 @@ def transform_block_filters(self, usage_info, block_structure):
                 if block_class is None:
                     logger.error('Failed to load block class for %s', block_key)
                     continue
-                block_keys = block_class.make_selection(selected, library_children, max_count)
+                # Seed deterministically so this transformer and the XBlock runtime's
+                # selected_children() path converge on the same selection for the same
+                # (user, block). See issue #38027.
+                seed = f"{usage_info.user.id}:{block_key}"
+                block_keys = block_class.make_selection(selected, library_children, max_count, seed=seed)
                 selected = block_keys['selected']
 
                 # Save back any changes

xmodule/item_bank_block.py

@@ -93,14 +93,19 @@ def completion_mode(cls):  # pylint: disable=no-self-argument
         return XBlockCompletionMode.AGGREGATOR
 
     @classmethod
-    def make_selection(cls, selected, children, max_count):
+    def make_selection(cls, selected, children, max_count, *, seed=None):
         """
         Dynamically selects block_ids indicating which of the possible children are displayed to the current user.
 
         Arguments:
             selected - list of (block_type, block_id) pairs assigned to this student
             children - children of this block
             max_count - number of components to display to each student
+            seed - optional deterministic seed (any hashable). When provided, two calls with the
+                   same seed, children, and max_count produce the same selection. Callers that run
+                   in independent code paths (e.g. the XBlock runtime and the ContentLibraryTransformer)
+                   MUST pass a stable seed derived from (user_id, block_usage_key) so that both paths
+                   converge on the same selection. See issue #38027.
 
         NOTE/TODO:
             We like to treat `self.selected` as a list of 2-tuples, but when we load a block from persistence, all
@@ -124,7 +129,7 @@ def make_selection(cls, selected, children, max_count):
             Order of invalid/overlimit/added is ALPHABETICAL, by type then id. This is arbitrary, but it makes the
             events more consistent and easier to test.
         """
-        rand = random.Random()
+        rand = random.Random(seed)
 
         selected_keys = {tuple(k) for k in selected}  # set of (block_type, block_id) tuples assigned to this student
 
@@ -156,7 +161,7 @@ def make_selection(cls, selected, children, max_count):
 
         if any((invalid_block_keys, overlimit_block_keys, added_block_keys)):
             selected = list(selected_keys)
-            random.shuffle(selected)
+            rand.shuffle(selected)
 
         return {
             'selected': selected,
@@ -249,7 +254,13 @@ def selected_children(self):
         if max_count < 0:
             max_count = len(self.children)
 
-        block_keys = self.make_selection(self.selected, self.children, max_count)  # pylint: disable=no-member
+        # Seed deterministically so the XBlock runtime and ContentLibraryTransformer,
+        # which both call make_selection independently on a page load, converge on the
+        # same selection. See issue #38027.
+        seed = f"{self.get_user_id()}:{self.usage_key}"
+        block_keys = self.make_selection(  # pylint: disable=no-member
+            self.selected, self.children, max_count, seed=seed,
+        )
 
         self.publish_selected_children_events(
             block_keys,

xmodule/tests/test_item_bank.py

@@ -520,3 +520,84 @@ def shuffle(_self, selection):
         return mock_result
 
     return shuffle
+
+
+class ItemBankMakeSelectionDeterminismTests(MixedSplitTestCase):
+    """
+    Regression tests for bug #38027: make_selection must be deterministic
+    across independent call sites when a seed is supplied, so that the XBlock
+    runtime and ContentLibraryTransformer converge on the same random subset
+    for a given (user, block) pair.
+    """
+
+    @staticmethod
+    def _children_pool(count=10):
+        """Build a simple children pool for make_selection."""
+        return [Mock(block_type="problem", block_id=f"p{i}") for i in range(count)]
+
+    def test_unit_make_selection_with_seed_is_deterministic(self):
+        """Same seed produces the same selection on every call."""
+        children = self._children_pool()
+        seed = "user-42:block-foo/bar"
+        first = ItemBankBlock.make_selection([], children, max_count=3, seed=seed)
+        for _ in range(5):
+            again = ItemBankBlock.make_selection([], children, max_count=3, seed=seed)
+            assert first['selected'] == again['selected']
+            assert first['added'] == again['added']
+
+    def test_unit_make_selection_different_seeds_can_differ(self):
+        """Different seeds across many users should produce at least two distinct subsets."""
+        children = self._children_pool()
+        subsets = set()
+        for uid in range(20):
+            result = ItemBankBlock.make_selection(
+                [], children, max_count=3, seed=f"user-{uid}:block-x",
+            )
+            subsets.add(tuple(sorted(result['selected'])))
+        assert len(subsets) > 1
+
+    def test_make_selection_preserves_signature_without_seed(self):
+        """
+        Backward compatibility: callers that don't pass seed still work
+        (keyword-only default is None).
+        """
+        children = self._children_pool()
+        result = ItemBankBlock.make_selection([], children, max_count=2)
+        assert len(result['selected']) == 2
+
+    def test_integration_transformer_and_xblock_seed_match(self):
+        """
+        Integration test for bug #38027: the XBlock runtime and transformer
+        produce the same selection for the same (user, block) pair because
+        they use the same seed format.
+        """
+        children = self._children_pool(8)
+        user_id = 777
+        block_key = "block-v1:Org+Course+Run+type@itembank+block@abc"
+        seed_from_xblock = f"{user_id}:{block_key}"
+        seed_from_transformer = f"{user_id}:{block_key}"
+
+        xblock_result = ItemBankBlock.make_selection(
+            [], children, max_count=3, seed=seed_from_xblock,
+        )
+        transformer_result = ItemBankBlock.make_selection(
+            [], children, max_count=3, seed=seed_from_transformer,
+        )
+        assert xblock_result['selected'] == transformer_result['selected']
+
+    def test_bug_38027_regression_selection_stable_across_rerun(self):
+        """
+        Regression for bug #38027: re-running make_selection with a non-empty
+        'selected' from a previous run must be a no-op (no shuffle, no
+        additions), so the learner's checkmark does not disappear on refresh.
+        """
+        children = self._children_pool(8)
+        seed = "user-777:block-abc"
+        first = ItemBankBlock.make_selection([], children, max_count=3, seed=seed)
+        second = ItemBankBlock.make_selection(
+            first['selected'], children, max_count=3, seed=seed,
+        )
+        assert second['added'] == []
+        assert second['invalid'] == []
+        assert second['overlimit'] == []
+        assert sorted(second['selected']) == sorted(first['selected'])