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 

2 files changed, 14 insertions, 9 deletions

diff --git a/src/libstd/thread_local/mod.rs b/src/libstd/thread_local/mod.rs
index f7a2f8e10e9..2a9bf452329 100644
--- a/src/libstd/thread_local/mod.rs
+++ b/src/libstd/thread_local/mod.rs
@@ -34,7 +34,7 @@
 //! will want to make use of some form of **interior mutability** through the
 //! `Cell` or `RefCell` types.
 
-#![stable]
+#![stable(feature = "rust1", since = "1.0.0")]
 
 use prelude::v1::*;
 
@@ -93,7 +93,7 @@ pub mod __impl {
 ///     assert_eq!(*f.borrow(), 2);
 /// });
 /// ```
-#[stable]
+#[stable(feature = "rust1", since = "1.0.0")]
 pub struct Key<T> {
     // The key itself may be tagged with #[thread_local], and this `Key` is
     // stored as a `static`, and it's not valid for a static to reference the
@@ -113,7 +113,7 @@ pub struct Key<T> {
 
 /// Declare a new thread local storage key of type `std::thread_local::Key`.
 #[macro_export]
-#[stable]
+#[stable(feature = "rust1", since = "1.0.0")]
 macro_rules! thread_local {
     (static $name:ident: $t:ty = $init:expr) => (
         static $name: ::std::thread_local::Key<$t> = {
@@ -218,7 +218,8 @@ macro_rules! __thread_local_inner {
 }
 
 /// Indicator of the state of a thread local storage key.
-#[unstable = "state querying was recently added"]
+#[unstable(feature = "std_misc",
+           reason = "state querying was recently added")]
 #[derive(Eq, PartialEq, Copy)]
 pub enum State {
     /// All keys are in this state whenever a thread starts. Keys will
@@ -258,7 +259,7 @@ impl<T: 'static> Key<T> {
     /// This function will `panic!()` if the key currently has its
     /// destructor running, and it **may** panic if the destructor has
     /// previously been run for this thread.
-    #[stable]
+    #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with<F, R>(&'static self, f: F) -> R
                       where F: FnOnce(&T) -> R {
         let slot = (self.inner)();
@@ -301,7 +302,8 @@ impl<T: 'static> Key<T> {
     /// initialization does not panic. Keys in the `Valid` state are guaranteed
     /// to be able to be accessed. Keys in the `Destroyed` state will panic on
     /// any call to `with`.
-    #[unstable = "state querying was recently added"]
+    #[unstable(feature = "std_misc",
+               reason = "state querying was recently added")]
     pub fn state(&'static self) -> State {
         unsafe {
             match (self.inner)().get() {
@@ -317,7 +319,9 @@ impl<T: 'static> Key<T> {
     }
 
     /// Deprecated
-    #[deprecated = "function renamed to state() and returns more info"]
+    #[unstable(feature = "std_misc")]
+    #[deprecated(since = "1.0.0",
+                 reason = "function renamed to state() and returns more info")]
     pub fn destroyed(&'static self) -> bool { self.state() == State::Destroyed }
 }
 
diff --git a/src/libstd/thread_local/scoped.rs b/src/libstd/thread_local/scoped.rs
index 1fb5652bc0c..1a20612d60a 100644
--- a/src/libstd/thread_local/scoped.rs
+++ b/src/libstd/thread_local/scoped.rs
@@ -38,8 +38,9 @@
 //! });
 //! ```
 
-#![unstable = "scoped TLS has yet to have wide enough use to fully consider \
-               stabilizing its interface"]
+#![unstable(feature = "std_misc",
+            reason = "scoped TLS has yet to have wide enough use to fully consider \
+                      stabilizing its interface")]
 
 use prelude::v1::*;