Fix #245, never introduce new nodes during discard

tobgu · Oct 22, 2023 · 07d60a5 · 07d60a5
1 parent 3fa47c2
commit 07d60a5
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diff --git a/pyrsistent/_transformations.py b/pyrsistent/_transformations.py
@@ -127,6 +127,10 @@ def _update_structure(structure, kvs, path, command):
         for k, v in kvs:
             is_empty = False
             if v is _EMPTY_SENTINEL:
+                if command is discard:
+                    # If nothing there when discarding just move on, do not introduce new nodes
+                    continue
+
                 # Allow expansion of structure but make sure to cover the case
                 # when an empty pmap is added as leaf node. See #154.
                 is_empty = True

diff --git a/tests/transform_test.py b/tests/transform_test.py
@@ -115,3 +115,8 @@ def test_discard_multiple_elements_in_pvector():
 def test_transform_insert_empty_pmap():
     m = pmap().transform(['123'], pmap())
     assert m == pmap({'123': pmap()})
+
+
+def test_discard_does_not_insert_nodes():
+    m = freeze({}).transform(['foo', 'bar'], discard)
+    assert m == pmap({})