meta: combine `net` and `dns`, use `parking_lot` (#2951)

This combines the `dns` and `net` feature flags. Previously, `dns` was
included as part of `net`. Given that is is rare that one would want
`dns` without `net`, DNS is now entirely gated w/ `net`.

The `parking_lot` feature is included as part of `full`.

Some misc docs are tweaked to reflect feature flag changes.

5 files changed, 14 insertions, 54 deletions

diff --git a/tokio/src/net/addr.rs b/tokio/src/net/addr.rs
index 86ae9919..7cbe531b 100644
--- a/tokio/src/net/addr.rs
+++ b/tokio/src/net/addr.rs
@@ -9,7 +9,7 @@ use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV
 ///
 /// Implementations of `ToSocketAddrs` for string types require a DNS lookup.
 /// These implementations are only provided when Tokio is used with the
-/// **`dns`** feature flag.
+/// **`net`** feature flag.
 ///
 /// # Calling
 ///
@@ -23,12 +23,13 @@ pub trait ToSocketAddrs: sealed::ToSocketAddrsPriv {}
 
 type ReadyFuture<T> = future::Ready<io::Result<T>>;
 
-#[cfg(any(feature = "dns", feature = "net"))]
-pub(crate) fn to_socket_addrs<T>(arg: T) -> T::Future
-where
-    T: ToSocketAddrs,
-{
-    arg.to_socket_addrs(sealed::Internal)
+cfg_net! {
+    pub(crate) fn to_socket_addrs<T>(arg: T) -> T::Future
+    where
+        T: ToSocketAddrs,
+    {
+        arg.to_socket_addrs(sealed::Internal)
+    }
 }
 
 // ===== impl &impl ToSocketAddrs =====
@@ -143,7 +144,7 @@ impl sealed::ToSocketAddrsPriv for &[SocketAddr] {
     }
 }
 
-cfg_dns! {
+cfg_net! {
     // ===== impl str =====
 
     impl ToSocketAddrs for str {}
@@ -256,7 +257,7 @@ pub(crate) mod sealed {
     #[allow(missing_debug_implementations)]
     pub struct Internal;
 
-    cfg_dns! {
+    cfg_net! {
         use crate::blocking::JoinHandle;
 
         use std::option;
diff --git a/tokio/src/net/lookup_host.rs b/tokio/src/net/lookup_host.rs
index 150228b5..28861849 100644
--- a/tokio/src/net/lookup_host.rs
+++ b/tokio/src/net/lookup_host.rs
@@ -1,4 +1,4 @@
-cfg_dns! {
+cfg_net! {
     use crate::net::addr::{self, ToSocketAddrs};
 
     use std::io;
diff --git a/tokio/src/net/mod.rs b/tokio/src/net/mod.rs
index f355356f..b7365e6d 100644
--- a/tokio/src/net/mod.rs
+++ b/tokio/src/net/mod.rs
@@ -27,12 +27,10 @@ mod addr;
 pub(crate) use addr::to_socket_addrs;
 pub use addr::ToSocketAddrs;
 
-cfg_dns! {
+cfg_net! {
     mod lookup_host;
     pub use lookup_host::lookup_host;
-}
 
-cfg_net! {
     pub mod tcp;
     pub use tcp::listener::TcpListener;
     pub use tcp::socket::TcpSocket;
diff --git a/tokio/src/net/tcp/listener.rs b/tokio/src/net/tcp/listener.rs
index 57500615..d3323ae0 100644
--- a/tokio/src/net/tcp/listener.rs
+++ b/tokio/src/net/tcp/listener.rs
@@ -80,7 +80,7 @@ impl TcpListener {
     /// method.
     ///
     /// The address type can be any implementor of the [`ToSocketAddrs`] trait.
-    /// Note that strings only implement this trait when the **`dns`** feature
+    /// Note that strings only implement this trait when the **`net`** feature
     /// is enabled, as strings may contain domain names that need to be resolved.
     ///
     /// If `addr` yields multiple addresses, bind will be attempted with each of
@@ -109,25 +109,6 @@ impl TcpListener {
     ///     Ok(())
     /// }
     /// ```
-    ///
-    /// Without the `dns` feature:
-    ///
-    /// ```no_run
-    /// use tokio::net::TcpListener;
-    /// use std::net::Ipv4Addr;
-    ///
-    /// use std::io;
-    ///
-    /// #[tokio::main]
-    /// async fn main() -> io::Result<()> {
-    ///     let listener = TcpListener::bind((Ipv4Addr::new(127, 0, 0, 1), 2345)).await?;
-    ///
-    ///     // use the listener
-    ///
-    ///     # let _ = listener;
-    ///     Ok(())
-    /// }
-    /// ```
     pub async fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<TcpListener> {
         let addrs = to_socket_addrs(addr).await?;
 
diff --git a/tokio/src/net/tcp/stream.rs b/tokio/src/net/tcp/stream.rs
index 7acab7db..f90e9a39 100644
--- a/tokio/src/net/tcp/stream.rs
+++ b/tokio/src/net/tcp/stream.rs
@@ -61,7 +61,7 @@ impl TcpStream {
     ///
     /// `addr` is an address of the remote host. Anything which implements the
     /// [`ToSocketAddrs`] trait can be supplied as the address. Note that
-    /// strings only implement this trait when the **`dns`** feature is enabled,
+    /// strings only implement this trait when the **`net`** feature is enabled,
     /// as strings may contain domain names that need to be resolved.
     ///
     /// If `addr` yields multiple addresses, connect will be attempted with each
@@ -90,26 +90,6 @@ impl TcpStream {
     /// }
     /// ```
     ///
-    /// Without the `dns` feature:
-    ///
-    /// ```no_run
-    /// use tokio::net::TcpStream;
-    /// use tokio::prelude::*;
-    /// use std::error::Error;
-    /// use std::net::Ipv4Addr;
-    ///
-    /// #[tokio::main]
-    /// async fn main() -> Result<(), Box<dyn Error>> {
-    ///     // Connect to a peer
-    ///     let mut stream = TcpStream::connect((Ipv4Addr::new(127, 0, 0, 1), 8080)).await?;
-    ///
-    ///     // Write some data.
-    ///     stream.write_all(b"hello world!").await?;
-    ///
-    ///     Ok(())
-    /// }
-    /// ```
-    ///
     /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
     ///
     /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all