SIFR-ASYNC-0006: Synchronous workload annotation applied to async function. - Sifr

SIFR-ASYNC-0006 belongs to the Async effect and awaitability diagnostic family. It means: synchronous workload annotation applied to async function.

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-0006 locally to see the renderer’s exact message template and any machine-applicable suggestions for the compiler version you are running.

Erroneous Code

@blocking_io
async def load() -> str:
    await task.sleep(0.0)
    return "done"

How To Fix It

Apply synchronous workload annotations to synchronous functions, not async functions.

Fixed Code

@blocking_io
def load() -> str:
    return read_text("config.txt")

Details

Field	Value
Code	`SIFR-ASYNC-0006`
Family	`ASYNC`
Severity	Error
Stability	stable
Owner	`sifr_lowering::lower::typing_and_functions`
Representative fixture	`crates/sifr/tests/e2e/fail/blocking_io_on_async_def_rejected.sifr`

See the Error Codes index for the complete catalog.