Accept any sequence shape for AsyncAdaptedCursor.description

PEP 249 specifies cursor.description as a sequence of sequences, not
a strict list. Pinning _Description to ``list[...] | None`` would
reject a dbapi cursor returning tuple-of-tuples (which SQLAlchemy's
own aiosqlite adapter accepts). Widen the alias to
Sequence[_DescriptionTuple] | None so the adapter passes the
description through verbatim.

Author: antoineleclair

src/sqlalchemydqlite/aio.py

@@ -26,8 +26,14 @@
 # Re-declared here (not imported) to keep the sqlalchemy-dqlite
 # runtime contract explicit to type-checkers even if the dbapi layer
 # later exposes a named alias.
+# PEP 249 specifies ``cursor.description`` as a sequence of sequences —
+# a ``list[tuple]`` is the canonical shape but a strict type alias of
+# ``list`` would reject a dbapi cursor that returns a tuple-of-tuples
+# (which sqlalchemy's own aiosqlite adapter accepts). Keep the alias
+# permissive so the adapter passes through whatever the underlying
+# cursor returns without copying.
 _DescriptionTuple = tuple[str, int | None, None, None, None, None, None]
-_Description = list[_DescriptionTuple] | None
+_Description = Sequence[_DescriptionTuple] | None
 
 
 class AsyncAdaptedCursor:

tests/test_async_adapter.py

@@ -461,3 +461,32 @@ def test_cursor_returns_async_adapted_cursor_wrapping_inner(self) -> None:
 
         cursor = adapter.cursor()
         assert isinstance(cursor, AsyncAdaptedCursor)
+
+
+class TestAsyncAdaptedCursorDescriptionType:
+    """``cursor.description`` is a PEP 249 sequence of sequences. The
+    adapter must accept (and pass through) any sequence the underlying
+    dbapi cursor returns — list, tuple, or other — without
+    converting."""
+
+    def test_description_passes_through_tuple_of_tuples(self) -> None:
+        cursor = _make_cursor()
+
+        mock_inner = MagicMock()
+        # Underlying cursor returns a tuple-of-tuples description.
+        mock_inner.description = (
+            ("id", 1, None, None, None, None, None),
+            ("name", 3, None, None, None, None, None),
+        )
+        mock_inner.lastrowid = None
+        mock_inner.rowcount = 0
+        mock_inner.execute.return_value = None
+        mock_inner.fetchall.return_value = []
+        mock_inner.close.return_value = None
+        cursor._connection.cursor.return_value = mock_inner
+
+        with patch("sqlalchemydqlite.aio.await_only", side_effect=_run_sync):
+            cursor.execute("SELECT id, name FROM t")
+
+        # Adapter must preserve the description untouched.
+        assert cursor.description == mock_inner.description