tor-rtmock: Introduce impl_runtime_prelude

This deduplicates some imports, which would otherwise be about to
become triplicated.

crates/tor-rtmock/src/net_runtime.rs

@@ -3,15 +3,9 @@
 // TODO(nickm): This is mostly copy-paste from MockSleepRuntime.  If possible,
 // we should make it so that more code is more shared.
 
-use crate::net::MockNetProvider;
-use tor_rtcompat::{BlockOn, Runtime, SleepProvider, TcpProvider, TlsProvider, UdpProvider};
+use crate::util::impl_runtime_prelude::*;
 
-use async_trait::async_trait;
-use futures::task::{FutureObj, Spawn, SpawnError};
-use futures::Future;
-use std::io::Result as IoResult;
-use std::net::SocketAddr;
-use std::time::{Duration, Instant, SystemTime};
+use crate::net::MockNetProvider;
 
 /// A wrapper Runtime that overrides the SleepProvider trait for the
 /// underlying runtime.

crates/tor-rtmock/src/sleep_runtime.rs

@@ -1,17 +1,12 @@
 //! Declare MockSleepRuntime.
 
-use crate::time::MockSleepProvider;
-use tor_rtcompat::{BlockOn, Runtime, SleepProvider, TcpProvider, TlsProvider, UdpProvider};
-
-use async_trait::async_trait;
-use futures::task::{FutureObj, Spawn, SpawnError};
-use futures::Future;
 use pin_project::pin_project;
-use std::io::Result as IoResult;
-use std::net::SocketAddr;
-use std::time::{Duration, Instant, SystemTime};
 use tracing::trace;
 
+use crate::time::MockSleepProvider;
+
+use crate::util::impl_runtime_prelude::*;
+
 /// A wrapper Runtime that overrides the SleepProvider trait for the
 /// underlying runtime.
 #[derive(Clone, Debug)]

crates/tor-rtmock/src/util.rs

@@ -96,3 +96,23 @@ macro_rules! impl_runtime { {
         }
     }
 } }
+
+/// Prelude that must be imported to use [`impl_runtime!`](impl_runtime)
+//
+// This could have been part of the expansion of `impl_runtime!`,
+// but it seems rather too exciting for a macro to import things as a side gig.
+//
+// Arguably this ought to be an internal crate::prelude instead.
+// But crate-internal preludes are controversial within the Arti team.  -Diziet
+//
+// For macro visibility reasons, this must come *lexically after* the macro,
+// to allow it to refer to the macro in the doc comment.
+pub(crate) mod impl_runtime_prelude {
+    pub(crate) use async_trait::async_trait;
+    pub(crate) use futures::task::{FutureObj, Spawn, SpawnError};
+    pub(crate) use futures::Future;
+    pub(crate) use std::io::Result as IoResult;
+    pub(crate) use std::net::SocketAddr;
+    pub(crate) use std::time::{Duration, Instant, SystemTime};
+    pub(crate) use tor_rtcompat::{BlockOn, Runtime, SleepProvider, TcpProvider, TlsProvider, UdpProvider};
+}