Fix segfault when closing cursor/connection after Statement.free()

src/firebird/driver/core.py

@@ -3965,7 +3965,13 @@ def _execute(self, operation: str | Statement,
                 in_meta.release()
     def _clear(self) -> None:
         if self._result is not None:
-            self._result.close()
+            if self._stmt is not None and self._stmt._istmt is not None:
+                self._result.close()
+            else:
+                # Statement was already freed; the result set is invalidated
+                # at the Firebird API level, so we must not call close() on it.
+                # Also prevent __del__ from calling release() on the invalid interface.
+                self._result._refcnt = 0
             self._result = None
         self._name = None
         self._last_fetch_status = None

tests/conftest.py

@@ -122,7 +122,7 @@ def pytest_configure(config):
             client_lib = Path(client_lib)
             if not client_lib.is_file():
                 pytest.exit(f"Client library '{client_lib}' not found!")
-            driver_config.fb_client_library.value = client_lib
+            driver_config.fb_client_library.value = str(client_lib)
         #
         if host := config.getoption('host'):
             _vars_['host'] = host

tests/test_issues.py

@@ -39,3 +39,29 @@ def test_issue_53(db_connection):
         numeric_val_exponent = numeric_val.as_tuple()[2]
         db_connection.commit()
         assert numeric_val_exponent == -2
+
+def test_issue_65_prepare_ctx_mgr(db_connection):
+    """Freeing a Statement via context manager must not crash when cursor/connection closes."""
+    with db_connection.cursor() as cur:
+        with cur.prepare('select count(*) from country where 1 < ?') as stmt:
+            row = cur.execute(stmt, (2,)).fetchone()
+            assert row is not None
+
+def test_issue_65_free_then_cursor_close(db_connection):
+    """Explicit stmt.free() followed by cursor.close() must not crash."""
+    cur = db_connection.cursor()
+    stmt = cur.prepare('select count(*) from country where 1 < ?')
+    row = cur.execute(stmt, (2,)).fetchone()
+    assert row is not None
+    stmt.free()
+    cur.close()
+
+def test_issue_65_free_then_conn_close(dsn):
+    """stmt.free() followed by connection close must not crash."""
+    from firebird.driver import connect
+    with connect(dsn) as conn:
+        cur = conn.cursor()
+        stmt = cur.prepare('select count(*) from country where 1 < ?')
+        row = cur.execute(stmt, (2,)).fetchone()
+        assert row is not None
+        stmt.free()