std: Second pass stabilization for `comm`

This commit is a second pass stabilization for the `std::comm` module,
performing the following actions:

* The entire `std::comm` module was moved under `std::sync::mpsc`. This movement
  reflects that channels are just yet another synchronization primitive, and
  they don't necessarily deserve a special place outside of the other
  concurrency primitives that the standard library offers.
* The `send` and `recv` methods have all been removed.
* The `send_opt` and `recv_opt` methods have been renamed to `send` and `recv`.
  This means that all send/receive operations return a `Result` now indicating
  whether the operation was successful or not.
* The error type of `send` is now a `SendError` to implement a custom error
  message and allow for `unwrap()`. The error type contains an `into_inner`
  method to extract the value.
* The error type of `recv` is now `RecvError` for the same reasons as `send`.
* The `TryRecvError` and `TrySendError` types have had public reexports removed
  of their variants and the variant names have been tweaked with enum
  namespacing rules.
* The `Messages` iterator is renamed to `Iter`

This functionality is now all `#[stable]`:

* `Sender`
* `SyncSender`
* `Receiver`
* `std::sync::mpsc`
* `channel`
* `sync_channel`
* `Iter`
* `Sender::send`
* `Sender::clone`
* `SyncSender::send`
* `SyncSender::try_send`
* `SyncSender::clone`
* `Receiver::recv`
* `Receiver::try_recv`
* `Receiver::iter`
* `SendError`
* `RecvError`
* `TrySendError::{mod, Full, Disconnected}`
* `TryRecvError::{mod, Empty, Disconnected}`
* `SendError::into_inner`
* `TrySendError::into_inner`

This is a breaking change due to the modification of where this module is
located, as well as the changing of the semantics of `send` and `recv`. Most
programs just need to rename imports of `std::comm` to `std::sync::mpsc` and
add calls to `unwrap` after a send or a receive operation.

[breaking-change]

1 files changed, 4 insertions, 4 deletions

diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
index b316cd908b6..3c4283c72e2 100644
--- a/src/libstd/sync/rwlock.rs
+++ b/src/libstd/sync/rwlock.rs
@@ -363,7 +363,7 @@ mod tests {
     use prelude::v1::*;
 
     use rand::{mod, Rng};
-    use comm::channel;
+    use sync::mpsc::channel;
     use thread::Thread;
     use sync::{Arc, RWLock, StaticRWLock, RWLOCK_INIT};
 
@@ -408,7 +408,7 @@ mod tests {
             }).detach();
         }
         drop(tx);
-        let _ = rx.recv_opt();
+        let _ = rx.recv();
         unsafe { R.destroy(); }
     }
 
@@ -475,7 +475,7 @@ mod tests {
                 Thread::yield_now();
                 *lock = tmp + 1;
             }
-            tx.send(());
+            tx.send(()).unwrap();
         }).detach();
 
         // Readers try to catch the writer in the act
@@ -494,7 +494,7 @@ mod tests {
         }
 
         // Wait for writer to finish
-        rx.recv();
+        rx.recv().unwrap();
         let lock = arc.read();
         assert_eq!(*lock, 10);
     }