Fix Array.__delitem__ corrupting rendered output on slice deletion

tests/test_items.py

@@ -357,6 +357,26 @@ def test_array_behaves_like_a_list() -> None:
     )
 
 
+def test_array_slice_deletion_keeps_render_in_sync() -> None:
+    # Regression: deleting a slice must keep as_string() consistent with the
+    # list contents. Slices with stop == 0 or negative bounds previously
+    # corrupted the rendered array (e.g. `del a[:0]` wiped every element).
+    a = item([1, 2, 3])
+    del a[:0]  # deletes nothing
+    assert a == [1, 2, 3]
+    assert a.as_string() == "[1, 2, 3]"
+
+    a = item([1, 2, 3])
+    del a[-1:]
+    assert a == [1, 2]
+    assert a.as_string() == "[1, 2]"
+
+    a = item([1, 2, 3])
+    del a[:-1]
+    assert a == [3]
+    assert a.as_string() == "[3]"
+
+
 def test_array_multiline() -> None:
     t = item([1, 2, 3, 4, 5, 6, 7, 8])
     t.multiline(True)

tomlkit/items.py

@@ -1657,9 +1657,7 @@ def __delitem__(self, key: int | slice) -> None:  # type: ignore[override]
         list.__delitem__(self, key)
 
         if isinstance(key, slice):
-            indices_to_remove = list(
-                range(key.start or 0, key.stop or length, key.step or 1)
-            )
+            indices_to_remove = list(range(*key.indices(length)))
         else:
             indices_to_remove = [length + key if key < 0 else key]
         for i in sorted(indices_to_remove, reverse=True):