docs: Add docs for dummy sleeper related

backon/src/lib.rs

@@ -125,7 +125,6 @@ mod sleep;
 pub use sleep::DefaultSleeper;
 #[cfg(all(target_arch = "wasm32", feature = "gloo-timers-sleep"))]
 pub use sleep::GlooTimersSleep;
-pub(crate) use sleep::PleaseEnableAFeatureForSleeper;
 pub use sleep::Sleeper;
 #[cfg(all(not(target_arch = "wasm32"), feature = "tokio-sleep"))]
 pub use sleep::TokioSleeper;

backon/src/retry.rs

@@ -264,13 +264,6 @@ where
     type Output = Result<T, E>;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        #[cfg(debug_assertions)]
-        if std::any::TypeId::of::<SF>()
-            == std::any::TypeId::of::<crate::PleaseEnableAFeatureForSleeper>()
-        {
-            panic!("BackON: No sleeper has been configured. Please enable the features or provide a custom implementation.")
-        }
-
         // Safety: This is safe because we don't move the `Retry` struct itself,
         // only its internal state.
         //

backon/src/retry_with_context.rs

@@ -303,13 +303,6 @@ where
     type Output = (Ctx, Result<T, E>);
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        #[cfg(debug_assertions)]
-        if std::any::TypeId::of::<SF>()
-            == std::any::TypeId::of::<crate::PleaseEnableAFeatureForSleeper>()
-        {
-            panic!("BackON: No sleeper has been configured. Please enable the features or provide a custom implementation.")
-        }
-
         // Safety: This is safe because we don't move the `Retry` struct itself,
         // only its internal state.
         //

backon/src/sleep.rs

@@ -3,6 +3,9 @@ use std::{
     time::Duration,
 };
 
+#[cfg(doc)]
+use crate::Retry;
+
 /// A sleeper is used to generate a future that completes after a specified duration.
 pub trait Sleeper: 'static {
     /// The future returned by the `sleep` method.
@@ -12,14 +15,16 @@ pub trait Sleeper: 'static {
     fn sleep(&self, dur: Duration) -> Self::Sleep;
 }
 
+/// A stub trait allowing non-[`Sleeper`] types to be used as a generic parameter in [`Retry`].
+/// It does not provide actual functionality.
 #[doc(hidden)]
 pub trait MayBeDefaultSleeper: 'static {
     type Sleep: Future<Output = ()>;
 }
 
-/// The default implementation of `Sleeper` is a no-op when no features are enabled.
-///
-/// It will panic on `debug` profile and do nothing on `release` profile.
+/// The default implementation of `Sleeper` when no features are enabled.
+/// It will fail to compile if a containing [`Retry`] is `.await`ed without calling [`Retry::sleep`]
+/// to provide a valid sleeper.
 #[cfg(all(not(feature = "tokio-sleep"), not(feature = "gloo-timers-sleep")))]
 pub type DefaultSleeper = PleaseEnableAFeatureForSleeper;
 /// The default implementation of `Sleeper` while feature `tokio-sleep` enabled.
@@ -33,7 +38,13 @@ pub type DefaultSleeper = TokioSleeper;
 #[cfg(all(target_arch = "wasm32", feature = "gloo-timers-sleep"))]
 pub type DefaultSleeper = GlooTimersSleep;
 
-/// The no-op implementation of `Sleeper` that does nothing.
+/// A stub type that does not implement [`Sleeper`] and hence will fail to compile if used as a
+/// sleeper.
+///
+/// Users are expected to enable a feature of this crate that provides a valid implementation of
+/// [`Sleeper`] when they see this type appearing in compilation errors. Otherwise, a custom [`Sleeper`]
+/// implementation should be provided where needed, such as [`Retry::sleeper`].
+#[doc(hidden)]
 #[derive(Clone, Copy, Debug, Default)]
 pub struct PleaseEnableAFeatureForSleeper;