Deprecate channel selection

src/libstd/sync/mpsc/mod.rs

@@ -124,6 +124,7 @@
 //! ```
 
 #![stable(feature = "rust1", since = "1.0.0")]
+#![allow(deprecated)] // for mpsc_select
 
 // A description of how Rust's channel implementation works
 //

src/libstd/sync/mpsc/select.rs

@@ -51,11 +51,10 @@
 #![unstable(feature = "mpsc_select",
             reason = "This implementation, while likely sufficient, is unsafe and \
                       likely to be error prone. At some point in the future this \
-                      module will likely be replaced, and it is currently \
-                      unknown how much API breakage that will cause. The ability \
-                      to select over a number of channels will remain forever, \
-                      but no guarantees beyond this are being made",
+                      module will be removed.",
             issue = "27800")]
+#![rustc_deprecated(since = "1.32.0",
+                    reason = "channel selection will be removed in a future release")]
 
 
 use fmt;