add @async.is_being_cancelled

Author: Guest0x0

src/async.mbt

@@ -38,6 +38,16 @@ pub using @event_loop {sleep}
 /// `pause` can be used to avoid starving other tasks.
 pub using @coroutine {pause}
 
+///|
+/// Returns `true` if current task is being cancelled.
+/// In this case, all work should be stopped except cleanup jobs.
+/// Usually there is no need to check for cancellation manually,
+/// the cancellation error will automatically get things done.
+/// However, some patterns, such as writing catch all error handler
+/// inside loop body, may result in infinite loop on cancellation.
+/// In this case, `is_being_cancelled` can be used to avoid dead loop.
+pub using @coroutine {is_being_cancelled}
+
 ///|
 pub suberror TimeoutError derive(Show)
 

src/pkg.generated.mbti

@@ -8,6 +8,8 @@ import(
 )
 
 // Values
+fn is_being_cancelled() -> Bool
+
 fn now() -> Int64
 
 async fn pause() -> Unit