Auto merge of #21248 - brson:feature-staging, r=alexcrichton

This implements the remaining bits of 'feature staging', as described in [RFC 507](https://github.com/rust-lang/rfcs/blob/master/text/0507-release-channels.md).

This is not quite done, but the substance of the work is complete so submitting for early review.

Key changes:
* `unstable`, `stable` and `deprecated` attributes all require 'feature' and 'since', and support an optional 'reason'.
* The `unstable` lint is removed.
* A new 'stability checking' pass warns when a used unstable library feature has not been activated with the `feature` attribute. At 1.0 beta this will become an error.
* A new 'unused feature checking' pass emits a lint ('unused_feature', renamed from 'unknown_feature') for any features that were activated but not used.
* A new tidy script `featureck.py` performs some global sanity checking, particularly that 'since' numbers agree, and also prints out a summary of features.

Differences from RFC:
* As implemented `unstable` requires a `since` attribute. I do not know if this is useful. I included it in the original sed script and just left it.
* RFC didn't specify the name of the optional 'reason' attribute.
* This continues to use 'unstable', 'stable' and 'deprecated' names (the 'nice' names) instead of 'staged_unstable', but only activates them with the crate-level 'staged_api' attribute.

I intend to update the RFC based on the outcome of this PR.

Issues:
* The unused feature check doesn't account for language features - i.e. you can activate a language feature, not use it, and not get the error.

Open questions:
* All unstable and deprecated features are named 'unnamed_feature', which i picked just because it is uniquely greppable. This is the 'catch-all' feature. What should it be?
* All stable features are named 'grandfathered'. What should this be?

TODO:
* Add check that all `deprecated` attributes are paired with a `stable` attribute in order to preserve the knowledge about when a feature became stable.
* Update rustdoc in various ways.
* Remove obsolete stability discussion from reference.
* Add features for 'path', 'io', 'os', 'hash' and 'rand'.

cc #20445 @alexcrichton @aturon 

1 files changed, 9 insertions, 9 deletions

diff --git a/src/libcore/array.rs b/src/libcore/array.rs
index a83537e12f7..44541c34ee2 100644
--- a/src/libcore/array.rs
+++ b/src/libcore/array.rs
@@ -12,7 +12,7 @@
 //! up to a certain length. Eventually we should able to generalize
 //! to all lengths.
 
-#![unstable] // not yet reviewed
+#![unstable(feature = "core")] // not yet reviewed
 
 use clone::Clone;
 use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
@@ -26,7 +26,7 @@ use option::Option;
 macro_rules! array_impls {
     ($($N:expr)+) => {
         $(
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<T:Copy> Clone for [T; $N] {
                 fn clone(&self) -> [T; $N] {
                     *self
@@ -39,14 +39,14 @@ macro_rules! array_impls {
                 }
             }
 
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<T: fmt::Debug> fmt::Debug for [T; $N] {
                 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                     fmt::Debug::fmt(&&self[], f)
                 }
             }
 
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<A, B> PartialEq<[B; $N]> for [A; $N] where A: PartialEq<B> {
                 #[inline]
                 fn eq(&self, other: &[B; $N]) -> bool {
@@ -58,7 +58,7 @@ macro_rules! array_impls {
                 }
             }
 
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<'a, A, B, Rhs> PartialEq<Rhs> for [A; $N] where
                 A: PartialEq<B>,
                 Rhs: Deref<Target=[B]>,
@@ -73,7 +73,7 @@ macro_rules! array_impls {
                 }
             }
 
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<'a, A, B, Lhs> PartialEq<[B; $N]> for Lhs where
                 A: PartialEq<B>,
                 Lhs: Deref<Target=[A]>
@@ -88,10 +88,10 @@ macro_rules! array_impls {
                 }
             }
 
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<T:Eq> Eq for [T; $N] { }
 
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<T:PartialOrd> PartialOrd for [T; $N] {
                 #[inline]
                 fn partial_cmp(&self, other: &[T; $N]) -> Option<Ordering> {
@@ -115,7 +115,7 @@ macro_rules! array_impls {
                 }
             }
 
-            #[stable]
+            #[stable(feature = "rust1", since = "1.0.0")]
             impl<T:Ord> Ord for [T; $N] {
                 #[inline]
                 fn cmp(&self, other: &[T; $N]) -> Ordering {