Reject negative size in AsyncAdaptedCursor.fetchmany

Both sibling cursors in dqlitedbapi (Cursor, AsyncCursor) raise
ProgrammingError on a negative size per ISSUE-82 and ISSUE-121. The
SQLAlchemy adapter was overlooked and silently returned [] under
min(size, len(rows)) for size<0. Surface the same ProgrammingError
so a caller bug (e.g. off-by-one on size) fails loudly and the
stack's cursors behave uniformly.

Author: antoineleclair

src/sqlalchemydqlite/aio.py

@@ -13,7 +13,12 @@
 from sqlalchemy.util import await_only
 
 from dqliteclient.exceptions import DqliteConnectionError
-from dqlitedbapi.exceptions import InterfaceError, NotSupportedError, OperationalError
+from dqlitedbapi.exceptions import (
+    InterfaceError,
+    NotSupportedError,
+    OperationalError,
+    ProgrammingError,
+)
 from sqlalchemydqlite.base import DqliteDialect
 
 logger = logging.getLogger(__name__)
@@ -136,6 +141,8 @@ def fetchone(self) -> Any:
     def fetchmany(self, size: int | None = None) -> Sequence[Any]:
         if size is None:
             size = self.arraysize
+        if size < 0:
+            raise ProgrammingError(f"fetchmany size must be non-negative, got {size}")
         return [self._rows.popleft() for _ in range(min(size, len(self._rows)))]
 
     def fetchall(self) -> Sequence[Any]:

tests/test_adapter_fetchmany_negative.py

@@ -0,0 +1,35 @@
+"""AsyncAdaptedCursor.fetchmany must reject negative size, matching
+the PEP-249 contract enforced by the two sibling dqlitedbapi cursors
+(ISSUE-82 and ISSUE-121).
+"""
+
+from __future__ import annotations
+
+from collections import deque
+from unittest.mock import MagicMock
+
+import pytest
+
+from dqlitedbapi.exceptions import ProgrammingError
+from sqlalchemydqlite.aio import AsyncAdaptedCursor
+
+
+def test_fetchmany_negative_size_raises_programming_error() -> None:
+    conn = MagicMock()
+    cur = AsyncAdaptedCursor(conn)
+    cur._rows = deque([("a",), ("b",)])
+
+    with pytest.raises(ProgrammingError, match="must be non-negative"):
+        cur.fetchmany(-1)
+
+    # Rows must not have been consumed on error.
+    assert len(cur._rows) == 2
+
+
+def test_fetchmany_zero_size_returns_empty() -> None:
+    """Existing behaviour: size=0 returns []."""
+    conn = MagicMock()
+    cur = AsyncAdaptedCursor(conn)
+    cur._rows = deque([("a",)])
+    assert list(cur.fetchmany(0)) == []
+    assert len(cur._rows) == 1