Python PEP249: track connections stored in class instance attributes

[Copilot]

SQL injection (and other PEP 249-based) queries miss findings when a connect() result is stored in a class attribute (self._conn) and later accessed via a getter method or direct attribute read — the TypeTracker cannot follow the value through __init__ because ReturnStep is blocked after a CallStep.

Changes

python/ql/lib/semmle/python/frameworks/PEP249.qll

• classStoresConnectionInInit(cls, attrName) — detects self.<attr> = dbapi.connect(...) in __init__
• ConnectionGetterAttributeRead (InstanceSource) — marks self._conn reads inside non-__init__ methods as connection sources. The AttrRead node for return self._conn is simultaneously the function's ExtractedReturnNode, so the existing returnStep propagates the type to all call sites for free
• ConnectionConstructorAttributeRead (InstanceSource) — marks MyClass()._conn direct attribute reads as connection sources, using DataFlowDispatch::resolveClassCall to confirm the constructor targets the right class

python/ql/test/library-tests/frameworks/hdbcli/pep249.py — test cases for the new patterns

python/ql/src/change-notes/2026-05-21-pep249-class-wrapper-connections.md — change note

Patterns now covered

class DatabaseConnection:
    def __init__(self):
        self._conn = dbapi.connect(...)

    def get_conn(self):
        return self._conn  # now an InstanceSource

hdb_con2 = DatabaseConnection().get_conn()  # tracked via returnStep
hdb_con3 = DatabaseConnection()._conn       # tracked as InstanceSource directly

db = DatabaseConnection()
db.get_conn().cursor().execute(query)       # full chain detected