chore: refine feature flags (#1785)

Removes dependencies between Tokio feature flags. For example, `process`
should not depend on `sync` simply because it uses the `mpsc` channel.
Instead, feature flags represent **public** APIs that become available
with the feature enabled. When the feature is not enabled, the
functionality is removed. If another Tokio component requires the
functionality, it is stays as `pub(crate)`.

The threaded scheduler is now exposed under `rt-threaded`. This feature
flag only enables the threaded scheduler and does not include I/O,
networking, or time. Those features must be explictly enabled.

A `full` feature flag is added that enables all features.

`stdin`, `stdout`, `stderr` are exposed under `io-std`.

Macros are used to scope code by feature flag.

1 files changed, 19 insertions, 21 deletions

diff --git a/tokio/src/net/mod.rs b/tokio/src/net/mod.rs
index 2ebf773f..50021e37 100644
--- a/tokio/src/net/mod.rs
+++ b/tokio/src/net/mod.rs
@@ -24,24 +24,22 @@
 mod addr;
 pub use addr::ToSocketAddrs;
 
-pub mod driver;
-
-pub mod util;
-
-#[cfg(feature = "tcp")]
-pub mod tcp;
-
-#[cfg(feature = "tcp")]
-pub use self::tcp::{TcpListener, TcpStream};
-
-#[cfg(feature = "udp")]
-pub mod udp;
-
-#[cfg(feature = "udp")]
-pub use self::udp::UdpSocket;
-
-#[cfg(all(unix, feature = "uds"))]
-pub mod unix;
-
-#[cfg(all(unix, feature = "uds"))]
-pub use self::unix::{UnixDatagram, UnixListener, UnixStream};
+cfg_io_driver! {
+    pub mod driver;
+    pub mod util;
+}
+
+cfg_tcp! {
+    pub mod tcp;
+    pub use tcp::{TcpListener, TcpStream};
+}
+
+cfg_udp! {
+    pub mod udp;
+    pub use udp::UdpSocket;
+}
+
+cfg_uds! {
+    pub mod unix;
+    pub use unix::{UnixDatagram, UnixListener, UnixStream};
+}