File-sink-async

Create a FileSink from an async context. The constructor opens the file with the native moonbitlang/async/fs interface and keeps the same rotation, policy, and failure-counter surface as file_sink(...).

Interface

pub async fn file_sink_async(
  path : String,
  append~ : Bool = true,
  auto_flush~ : Bool = true,
  rotation~ : FileRotation? = None,
  formatter~ : RecordFormatter = fn(rec) { format_text(rec) },
) -> FileSink {}

input

• path : String - Destination file path.
• append : Bool - Whether writes append rather than truncate on the first open.
• auto_flush : Bool - Whether each async write requests an async file sync.
• rotation : FileRotation? - Optional size-based rotation policy.
• formatter : RecordFormatter - Formatter used to render each record.

output

• FileSink - A file sink ready for use by an async logger or direct async sink writes.

Explanation

• Use this constructor when the caller is already running inside an async event loop.
• File writes, flushes, file-size checks, renames, removals, and rotation reopening use the async filesystem path.
• The returned sink implements Sink::write_async(...); the synchronous write(...) surface remains available for synchronous callers.
• On non-native targets, the sink follows the existing unavailable-backend behavior.

How to Use

let sink = file_sink_async("app.log", auto_flush=false)
let logger = async_logger(sink)

Error Case

• If the initial async open fails, the returned sink is unavailable and increments open_failures().
• Later async writes record write and rotation failures through the existing sink counters.

Notes

1. Use file_sink(...) for synchronous construction outside an async event loop.

2. Pair this API with native_files_supported() when code must also compile for non-native targets.