add experimental async/await support. (#582)

This patch adds experimental async/await support to Tokio. It does this
by adding feature flags to existing libs only where necessary in order
to add nightly specific code (mostly `Unpin` implementations). It then
provides a new crate: `tokio-async-await` which is a shim layer on top
of `tokio`.

The `tokio-async-await` crate is expected to look exactly like `tokio`
does, but with async / await support. This strategy reduces the amount
of cfg guarding in the main libraries.

This patch also adds `tokio-channel`, which is copied from futures-rs
0.1 and adds the necessary `Unpin` implementations. In general, futures
0.1 is mostly unmaintained, so it will make sense for Tokio to take over
maintainership of key components regardless of async / await support.

4 files changed, 25 insertions, 3 deletions

diff --git a/tokio-reactor/CHANGELOG.md b/tokio-reactor/CHANGELOG.md
index e7bd54d8..344a6928 100644
--- a/tokio-reactor/CHANGELOG.md
+++ b/tokio-reactor/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 0.1.5 (August 27, 2018)
+
+* Experimental async / await support.
+
 # 0.1.4 (August 23, 2018)
 
 * Use a scalable RW lock (#517)
diff --git a/tokio-reactor/Cargo.toml b/tokio-reactor/Cargo.toml
index 85901c5d..7861204e 100644
--- a/tokio-reactor/Cargo.toml
+++ b/tokio-reactor/Cargo.toml
@@ -6,18 +6,23 @@ name = "tokio-reactor"
 # - Update CHANGELOG.md.
 # - Update doc URL.
 # - Create "v0.1.x" git tag.
-version = "0.1.4"
+version = "0.1.5"
 authors = ["Carl Lerche <me@carllerche.com>"]
 license = "MIT"
 readme = "README.md"
 repository = "https://github.com/tokio-rs/tokio"
 homepage = "https://tokio.rs"
-documentation = "https://docs.rs/tokio-reactor/0.1.4/tokio_reactor"
+documentation = "https://docs.rs/tokio-reactor/0.1.5/tokio_reactor"
 description = """
 Event loop that drives Tokio I/O resources.
 """
 categories = ["asynchronous", "network-programming"]
 
+[features]
+# This feature comes with no promise of stability. Things will break with each
+# patch release. Use at your own risk.
+async-await-preview = []
+
 [dependencies]
 crossbeam-utils = "0.5.0"
 futures = "0.1.19"
diff --git a/tokio-reactor/src/async_await.rs b/tokio-reactor/src/async_await.rs
new file mode 100644
index 00000000..698f285c
--- /dev/null
+++ b/tokio-reactor/src/async_await.rs
@@ -0,0 +1,5 @@
+use Registration;
+
+use std::marker::Unpin;
+
+impl Unpin for Registration {}
diff --git a/tokio-reactor/src/lib.rs b/tokio-reactor/src/lib.rs
index 3dff5782..eeefb7d0 100644
--- a/tokio-reactor/src/lib.rs
+++ b/tokio-reactor/src/lib.rs
@@ -1,5 +1,8 @@
-#![doc(html_root_url = "https://docs.rs/tokio-reactor/0.1.4")]
+#![doc(html_root_url = "https://docs.rs/tokio-reactor/0.1.5")]
 #![deny(missing_docs, warnings, missing_debug_implementations)]
+#![cfg_attr(feature = "async-await-preview", feature(
+        pin,
+        ))]
 
 //! Event loop that drives Tokio I/O resources.
 //!
@@ -756,3 +759,8 @@ impl Error for SetFallbackError {
         "attempted to set fallback reactor while already configured"
     }
 }
+
+// ===== EXPERIMENTAL async / await support =====
+
+#[cfg(feature = "async-await-preview")]
+mod async_await;