doc feature flags in futures

futures/src/executor/async_std.rs

@@ -3,6 +3,7 @@ use crate::Executor;
 use futures::Future;
 
 /// An `async-std` runtime.
+#[cfg_attr(docsrs, doc(cfg(feature = "async-std")))]
 #[derive(Debug)]
 pub struct AsyncStd;
 

futures/src/executor/thread_pool.rs

@@ -3,6 +3,7 @@ use crate::Executor;
 use futures::Future;
 
 /// A thread pool runtime for futures.
+#[cfg_attr(docsrs, doc(cfg(feature = "thread-pool")))]
 pub type ThreadPool = futures::executor::ThreadPool;
 
 impl Executor for futures::executor::ThreadPool {

futures/src/executor/tokio.rs

@@ -3,6 +3,7 @@ use crate::Executor;
 use futures::Future;
 
 /// A `tokio` runtime.
+#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
 pub type Tokio = tokio::runtime::Runtime;
 
 impl Executor for Tokio {

futures/src/lib.rs

@@ -4,6 +4,8 @@
 #![deny(unused_results)]
 #![forbid(unsafe_code)]
 #![forbid(rust_2018_idioms)]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
 pub use futures;
 
 mod command;