Remove dead futures2 code. (#538)

The futures 0.2 crate is not intended for widespread usage. Also, the
futures team is exploring the compat shim route.

If futures 0.3 support is added to Tokio 0.1, then a different
integration route will be explored, making the current code unhelpful.

tokio-executor/src/enter.rs

@@ -3,9 +3,6 @@ use std::cell::Cell;
 use std::error::Error;
 use std::fmt;
 
-#[cfg(feature = "unstable-futures")]
-use futures2;
-
 thread_local!(static ENTERED: Cell<bool> = Cell::new(false));
 
 /// Represents an executor context.
@@ -14,9 +11,6 @@ thread_local!(static ENTERED: Cell<bool> = Cell::new(false));
 pub struct Enter {
     on_exit: Vec<Box<Callback>>,
     permanent: bool,
-
-    #[cfg(feature = "unstable-futures")]
-    _enter2: futures2::executor::Enter,
 }
 
 /// An error returned by `enter` if an execution scope has already been
@@ -66,9 +60,6 @@ pub fn enter() -> Result<Enter, EnterError> {
             Ok(Enter {
                 on_exit: Vec::new(),
                 permanent: false,
-
-                #[cfg(feature = "unstable-futures")]
-                _enter2: futures2::executor::enter().unwrap(),
             })
         }
     })

tokio-executor/src/global.rs

@@ -4,9 +4,6 @@ use futures::Future;
 
 use std::cell::Cell;
 
-#[cfg(feature = "unstable-futures")]
-use futures2;
-
 /// Executes futures on the default executor for the current execution context.
 ///
 /// `DefaultExecutor` implements `Executor` and can be used to spawn futures
@@ -65,7 +62,7 @@ enum State {
     Ready(*mut Executor),
     // default executor is currently active (used to detect recursive calls)
     Active
-} 
+}
 
 /// Thread-local tracking the current executor
 thread_local!(static EXECUTOR: Cell<State> = Cell::new(State::Empty));
@@ -80,14 +77,6 @@ impl super::Executor for DefaultExecutor {
             .unwrap_or_else(|| Err(SpawnError::shutdown()))
     }
 
-    #[cfg(feature = "unstable-futures")]
-    fn spawn2(&mut self, future: Box<futures2::Future<Item = (), Error = futures2::Never> + Send>)
-             -> Result<(), futures2::executor::SpawnError>
-    {
-        DefaultExecutor::with_current(|executor| executor.spawn2(future))
-            .unwrap_or_else(|| Err(futures2::executor::SpawnError::shutdown()))
-    }
-
     fn status(&self) -> Result<(), SpawnError> {
         DefaultExecutor::with_current(|executor| executor.status())
             .unwrap_or_else(|| Err(SpawnError::shutdown()))
@@ -142,15 +131,6 @@ pub fn spawn<T>(future: T)
         .unwrap()
 }
 
-/// Like `spawn` but compatible with futures 0.2
-#[cfg(feature = "unstable-futures")]
-pub fn spawn2<T>(future: T)
-    where T: futures2::Future<Item = (), Error = futures2::Never> + Send + 'static,
-{
-    DefaultExecutor::current().spawn2(Box::new(future))
-        .unwrap()
-}
-
 /// Set the default executor for the duration of the closure
 ///
 /// # Panics

tokio-executor/src/lib.rs

@@ -37,9 +37,6 @@
 
 extern crate futures;
 
-#[cfg(feature = "unstable-futures")]
-extern crate futures2;
-
 mod enter;
 mod global;
 pub mod park;
@@ -47,9 +44,6 @@ pub mod park;
 pub use enter::{enter, Enter, EnterError};
 pub use global::{spawn, with_default, DefaultExecutor};
 
-#[cfg(feature = "unstable-futures")]
-pub use global::spawn2;
-
 use futures::Future;
 
 use std::error::Error;
@@ -142,11 +136,6 @@ pub trait Executor {
     fn spawn(&mut self, future: Box<Future<Item = (), Error = ()> + Send>)
              -> Result<(), SpawnError>;
 
-    /// Like `spawn`, but compatible with futures 0.2
-    #[cfg(feature = "unstable-futures")]
-    fn spawn2(&mut self, future: Box<futures2::Future<Item = (), Error = futures2::Never> + Send>)
-             -> Result<(), futures2::executor::SpawnError>;
-
     /// Provides a best effort **hint** to whether or not `spawn` will succeed.
     ///
     /// This function may return both false positives **and** false negatives.
@@ -194,13 +183,6 @@ impl<E: Executor + ?Sized> Executor for Box<E> {
         (**self).spawn(future)
     }
 
-    #[cfg(feature = "unstable-futures")]
-    fn spawn2(&mut self, future: Box<futures2::Future<Item = (), Error = futures2::Never> + Send>)
-        -> Result<(), futures2::executor::SpawnError>
-    {
-        (**self).spawn2(future)
-    }
-
     fn status(&self) -> Result<(), SpawnError> {
         (**self).status()
     }