diem/diem · error

Failed to generate txn effects

Error message

Failed to generate txn effects

What it means

In the e2e test executor's exec(), after executing a function in a Move session, session.finish() is unwrapped with this panic message. It fires when the session cannot produce a changeset (e.g. the transaction aborted mid-execution leaving inconsistent state, or resource/enum deserialization problems).

Source

Thrown at language/testing-infra/e2e-tests/src/executor.rs:512

            let remote_view = RemoteStorage::new(&self.data_store);
            let mut session = vm.new_session(&remote_view);
            session
                .execute_function(
                    &Self::module(module_name),
                    &Self::name(function_name),
                    type_params,
                    args,
                    &mut gas_status,
                )
                .unwrap_or_else(|e| {
                    panic!(
                        "Error calling {}.{}: {}",
                        module_name,
                        function_name,
                        e.into_vm_status()
                    )
                });
            let (changeset, events) = session.finish().expect("Failed to generate txn effects");
            let (writeset, _events) = convert_changeset_and_events(changeset, events)
                .expect("Failed to generate writeset");
            writeset
        };
        self.data_store.add_write_set(&write_set);
    }

    pub fn try_exec(
        &mut self,
        module_name: &str,
        function_name: &str,
        type_params: Vec<TypeTag>,
        args: Vec<Vec<u8>>,
    ) -> Result<WriteSet, VMStatus> {
        let mut gas_status = GasStatus::new_unmetered();
        let vm = MoveVM::new(diem_vm::natives::diem_natives()).unwrap();
        let remote_view = RemoteStorage::new(&self.data_store);
        let mut session = vm.new_session(&remote_view);

View on GitHub (pinned to fc4714a8ea)

Solutions

1. Check the preceding 'Error calling module.function' log message to find the abort cause and fix the called Move code or test inputs.
2. Use try_exec (which maps errors to VMStatus) instead of exec for transactions expected to fail.
3. Ensure the data store state is fresh/valid (e.g. don't re-initialize an already initialized chain).

Example fix

// before
executor.exec(initialize_script, ...); // aborts -> panic in session.finish()
// after
executor.try_exec(initialize_script, ...).expect("init should succeed");

// prefer try_exec when a transaction may abort
let result = executor.try_exec(&script, ty_args, args);

match std::panic::catch_unwind(|| executor.exec(...)) {
    Ok(ws) => use(ws),
    Err(p) if panic_msg_contains(p, "Failed to generate txn effects") =>
        eprintln!("check the 'Error calling module.function' log above"),
    Err(p) => resume_unwind(p),
}

When it happens

Trigger: Calling exec (used by test_diem_initialize, publish_and_register_new_currency, etc.) when the underlying MoveVM session finish() returns an error — typically an aborted transaction or invalid state update.

Common situations: Tests that call exec with scripts/functions that abort, or data store state inconsistent with what the session expects (e.g. initializing Diem twice).

Related errors

• Failed to generate writeset
• Input value has too small of a fractional part 1/{}, but sma
• Input value is too big: {:?}, max: {:?}
• invalid value
• Aborted command

AI-assisted analysis of diem/diem@fc4714a8ea (2026-09-04). Data as JSON: /api/errors/88881ebc805e664c. Report an issue: GitHub.