Add test documenting missing PEP249 alerts for connection stored in self attribute

python/ql/test/library-tests/frameworks/hdbcli/pep249.py

@@ -7,3 +7,31 @@ cursor.execute("some sql", (42,))  # $ getSql="some sql"
 cursor.executemany("some sql", (42,))  # $ getSql="some sql"
     
 cursor.close()
+
+
+# Connection stored in a class attribute (`self._conn`) and used in another method.
+#
+# This is currently NOT detected: the `Connection::instance()`/`execute()` predicates in
+# PEP249.qll are based on type tracking, which cannot follow a value that is stored into a
+# `self` attribute in one method and read from a `self` attribute in another method (see the
+# `MISSING` markers below). Regular (global) data flow handles this case correctly, so the
+# limitation is specific to the type-tracking-based modeling.
+class Database:
+    def __init__(self):
+        self._conn = dbapi.connect(address="hostname", port=300, user="username")
+
+    def get_connection(self):
+        return self._conn
+
+    def run_via_getter(self):
+        conn = self.get_connection()
+        cursor = conn.cursor()
+        cursor.execute("getter sql")  # $ MISSING: getSql="getter sql"
+
+    def run_direct(self):
+        self._conn.execute("direct sql")  # $ MISSING: getSql="direct sql"
+
+
+db = Database()
+db.run_via_getter()
+db.run_direct()