Fix PDeque.remove() and PDeque.reverse() dropping maxlen

CHANGES.txt

@@ -1,5 +1,10 @@
 Revision history
 ----------------
+unreleased
+ * Fix PDeque.remove() and PDeque.reverse() dropping the maxlen of a bounded
+   deque, which silently unbounded the result so later appends could grow it
+   past its declared maximum length.
+
 0.21.0, 2026-01-11
  * Drop official support for Python 3.8 and 3.9, these versions are no longer part of the test matrix.
  * Add Python 3.13 and 3.14 to test matrix and re-establish test coverage.

pyrsistent/_pdeque.py

@@ -272,13 +272,13 @@ def remove(self, elem):
         pdeque([1, 2])
         """
         try:
-            return PDeque(self._left_list.remove(elem), self._right_list, self._length - 1)
+            return PDeque(self._left_list.remove(elem), self._right_list, self._length - 1, self._maxlen)
         except ValueError:
             # Value not found in left list, try the right list
             try:
                 # This is severely inefficient with a double reverse, should perhaps implement a remove_last()?
                 return PDeque(self._left_list,
-                              self._right_list.reverse().remove(elem).reverse(), self._length - 1)
+                              self._right_list.reverse().remove(elem).reverse(), self._length - 1, self._maxlen)
             except ValueError as e:
                 raise ValueError('{0} not found in PDeque'.format(elem)) from e
 
@@ -294,7 +294,7 @@ def reverse(self):
         >>> reversed(pdeque([1, 2, 3]))
         pdeque([3, 2, 1])
         """
-        return PDeque(self._right_list, self._left_list, self._length)
+        return PDeque(self._right_list, self._left_list, self._length, self._maxlen)
     __reversed__ = reverse
 
     def rotate(self, steps):

tests/deque_test.py

@@ -169,6 +169,14 @@ def test_remove():
     assert pdeque([1, 2, 3, 3, 4, 5, 4, 6]).remove(4) == pdeque([1, 2, 3, 3, 5, 4, 6])
 
 
+def test_remove_preserves_maxlen():
+    # A bounded deque must stay bounded after a remove, or later appends grow
+    # it past maxlen.
+    x = pdeque([1, 2, 3], maxlen=3).remove(2)
+    assert x.maxlen == 3
+    assert x.append(4).append(5) == pdeque([3, 4, 5], maxlen=3)
+
+
 def test_remove_element_missing():
     with pytest.raises(ValueError):
         pdeque().remove(2)
@@ -182,6 +190,12 @@ def test_reverse():
     assert pdeque().reverse() == pdeque()
 
 
+def test_reverse_preserves_maxlen():
+    x = pdeque([1, 2, 3], maxlen=3).reverse()
+    assert x.maxlen == 3
+    assert x.append(4) == pdeque([2, 1, 4], maxlen=3)
+
+
 def test_rotate_right():
     assert pdeque([1, 2, 3, 4, 5]).rotate(2) == pdeque([4, 5, 1, 2, 3])
     assert pdeque([1, 2]).rotate(0) == pdeque([1, 2])