SIFR-ASYNC-0002: Awaited same-task coroutine has no real suspension effect. - Sifr

SIFR-ASYNC-0002 belongs to the Async effect and awaitability diagnostic family. It means: awaited same-task coroutine has no real suspension effect.

Why It Happens

Sifr tracks suspension and blocking effects statically. This diagnostic fires when async code either does not really suspend, awaits work that cannot suspend, or calls blocking/CPU-heavy work without an explicit offload boundary.

Use sifr --explain SIFR-ASYNC-0002 locally to see the renderer’s exact message template and any machine-applicable suggestions for the compiler version you are running.

Erroneous Code

async def cached() -> int:
    return 1

async def main() -> int:
    return await cached()

How To Fix It

Do not await a same-task coroutine that cannot suspend. Make the helper synchronous, or move the suspension into the helper.

Fixed Code

def cached() -> int:
    return 1

async def main() -> int:
    await task.sleep(0.0)
    return cached()

Details

Field	Value
Code	`SIFR-ASYNC-0002`
Family	`ASYNC`
Severity	Error
Stability	stable
Owner	`sifr_lowering::lower::async_await`
Representative fixture	`crates/sifr/tests/e2e/fail/async_transitive_no_suspend_await_rejected.sifr`

See the Error Codes index for the complete catalog.