Fix segfault when closing cursor/connection after Statement.free(). Fix #65.

When a Statement was freed (via context manager or explicit free()) before
its Cursor was closed, Cursor._clear() would attempt to close an already-
invalidated IResultSet, causing a segfault or DatabaseError.

Now checks whether the Statement's interface is still valid before closing
the result set. If the statement was already freed, the result set reference
is safely discarded instead.

Author: fdcastel

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()