Auto merge of #43017 - durka:stabilize-const-invocation, r=eddyb

Individualize feature gates for const fn invocation

This PR changes the meaning of `#![feature(const_fn)]` so it is only required to declare a const fn but not to call one. Based on discussion at #24111. I was hoping we could have an FCP here in order to move that conversation forward.

This sets the stage for future stabilization of the constness of several functions in the standard library (listed below), so could someone please tag the lang team for review.

- `std::cell`
    - `Cell::new`
    - `RefCell::new`
    - `UnsafeCell::new`
- `std::mem`
    - `size_of`
    - `align_of`
- `std::ptr`
    - `null`
    - `null_mut`
- `std::sync`
    - `atomic`
        - `Atomic{Bool,Ptr,Isize,Usize}::new`
    - `once`
        - `Once::new`
- primitives
    - `{integer}::min_value`
    - `{integer}::max_value`

Some other functions are const but they are also unstable or hidden, e.g. `Unique::new` so they don't have to be considered at this time.

After this stabilization, the following `*_INIT` constants in the standard library can be deprecated. I wasn't sure whether to include those deprecations in the current PR.

- `std::sync`
    - `atomic`
        - `ATOMIC_{BOOL,ISIZE,USIZE}_INIT`
    - `once`
        - `ONCE_INIT`

src/Cargo.lock

@@ -1346,7 +1346,7 @@ dependencies = [
  "lazy_static 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "racer 2.0.10 (registry+https://github.com/rust-lang/crates.io-index)",
- "rls-analysis 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rls-analysis 0.6.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "rls-data 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rls-rustc 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rls-span 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1360,7 +1360,7 @@ dependencies = [
 
 [[package]]
 name = "rls-analysis"
-version = "0.6.5"
+version = "0.6.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "derive-new 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2555,7 +2555,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum regex 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "1731164734096285ec2a5ec7fea5248ae2f5485b3feeb0115af4fda2183b2d1b"
 "checksum regex-syntax 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "f9ec002c35e86791825ed294b50008eea9ddfc8def4420124fbc6b08db834957"
 "checksum regex-syntax 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "ad890a5eef7953f55427c50575c680c42841653abd2b028b68cd223d157f62db"
-"checksum rls-analysis 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)" = "d2cb40c0371765897ae428b5706bb17135705ad4f6d1b8b6afbaabcf8c9b5cff"
+"checksum rls-analysis 0.6.7 (registry+https://github.com/rust-lang/crates.io-index)" = "4302cc8291570d7f817945845d8c01756e833dbc93c0a87d4f6c9a0b0b7992f1"
 "checksum rls-data 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "11d339f1888e33e74d8032de0f83c40b2bdaaaf04a8cfc03b32186c3481fb534"
 "checksum rls-rustc 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b21ea952e9bf1569929abf1bb920262cde04b7b1b26d8e0260286302807299d2"
 "checksum rls-span 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5d7c7046dc6a92f2ae02ed302746db4382e75131b9ce20ce967259f6b5867a6a"

src/libcore/cell.rs

@@ -329,6 +329,7 @@ impl<T> Cell<T> {
     /// let c = Cell::new(5);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_cell_new"))]
     #[inline]
     pub const fn new(value: T) -> Cell<T> {
         Cell {
@@ -543,6 +544,7 @@ impl<T> RefCell<T> {
     /// let c = RefCell::new(5);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_refcell_new"))]
     #[inline]
     pub const fn new(value: T) -> RefCell<T> {
         RefCell {
@@ -1188,6 +1190,7 @@ impl<T> UnsafeCell<T> {
     /// let uc = UnsafeCell::new(5);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_unsafe_cell_new"))]
     #[inline]
     pub const fn new(value: T) -> UnsafeCell<T> {
         UnsafeCell { value: value }

src/libcore/lib.rs

@@ -85,12 +85,30 @@
 #![feature(prelude_import)]
 #![feature(repr_simd, platform_intrinsics)]
 #![feature(rustc_attrs)]
+#![cfg_attr(not(stage0), feature(rustc_const_unstable))]
 #![feature(specialization)]
 #![feature(staged_api)]
 #![feature(unboxed_closures)]
 #![feature(untagged_unions)]
 #![feature(unwind_attributes)]
 
+#![cfg_attr(not(stage0), feature(const_min_value))]
+#![cfg_attr(not(stage0), feature(const_max_value))]
+#![cfg_attr(not(stage0), feature(const_atomic_bool_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_isize_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_usize_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_i8_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_u8_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_i16_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_u16_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_i32_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_u32_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_i64_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_u64_new))]
+#![cfg_attr(not(stage0), feature(const_unsafe_cell_new))]
+#![cfg_attr(not(stage0), feature(const_cell_new))]
+#![cfg_attr(not(stage0), feature(const_nonzero_new))]
+
 #[prelude_import]
 #[allow(unused)]
 use prelude::v1::*;

src/libcore/mem.rs

@@ -189,6 +189,7 @@ pub fn forget<T>(t: T) {
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_size_of"))]
 pub const fn size_of<T>() -> usize {
     unsafe { intrinsics::size_of::<T>() }
 }
@@ -280,6 +281,7 @@ pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_align_of"))]
 pub const fn align_of<T>() -> usize {
     unsafe { intrinsics::min_align_of::<T>() }
 }

src/libcore/nonzero.rs

@@ -68,6 +68,10 @@ pub struct NonZero<T: Zeroable>(T);
 impl<T: Zeroable> NonZero<T> {
     /// Creates an instance of NonZero with the provided value.
     /// You must indeed ensure that the value is actually "non-zero".
+    #[unstable(feature = "nonzero",
+               reason = "needs an RFC to flesh out the design",
+               issue = "27730")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_nonzero_new"))]
     #[inline]
     pub const unsafe fn new_unchecked(inner: T) -> Self {
         NonZero(inner)

src/libcore/num/mod.rs

@@ -109,6 +109,7 @@ macro_rules! int_impl {
         /// assert_eq!(i8::min_value(), -128);
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
+        #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_min_value"))]
         #[inline]
         pub const fn min_value() -> Self {
             !0 ^ ((!0 as $UnsignedT) >> 1) as Self
@@ -122,6 +123,7 @@ macro_rules! int_impl {
         /// assert_eq!(i8::max_value(), 127);
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
+        #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_max_value"))]
         #[inline]
         pub const fn max_value() -> Self {
             !Self::min_value()
@@ -1280,6 +1282,7 @@ macro_rules! uint_impl {
         /// assert_eq!(u8::min_value(), 0);
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
+        #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_min_value"))]
         #[inline]
         pub const fn min_value() -> Self { 0 }
 
@@ -1291,6 +1294,7 @@ macro_rules! uint_impl {
         /// assert_eq!(u8::max_value(), 255);
         /// ```
         #[stable(feature = "rust1", since = "1.0.0")]
+        #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_max_value"))]
         #[inline]
         pub const fn max_value() -> Self { !0 }
 

src/libcore/ptr.rs

@@ -76,6 +76,7 @@ pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_ptr_null"))]
 pub const fn null<T>() -> *const T { 0 as *const T }
 
 /// Creates a null mutable raw pointer.
@@ -90,6 +91,7 @@ pub const fn null<T>() -> *const T { 0 as *const T }
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_ptr_null_mut"))]
 pub const fn null_mut<T>() -> *mut T { 0 as *mut T }
 
 /// Swaps the values at two mutable locations of the same type, without
@@ -1097,6 +1099,8 @@ impl<T: ?Sized> Unique<T> {
     /// # Safety
     ///
     /// `ptr` must be non-null.
+    #[unstable(feature = "unique", issue = "27730")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_unique_new"))]
     pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
         Unique { pointer: NonZero::new_unchecked(ptr), _marker: PhantomData }
     }
@@ -1230,6 +1234,8 @@ impl<T: ?Sized> Shared<T> {
     /// # Safety
     ///
     /// `ptr` must be non-null.
+    #[unstable(feature = "shared", issue = "27730")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_shared_new"))]
     pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
         Shared { pointer: NonZero::new_unchecked(ptr), _marker: PhantomData }
     }

src/libcore/sync/atomic.rs

@@ -241,6 +241,7 @@ impl AtomicBool {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_atomic_bool_new"))]
     pub const fn new(v: bool) -> AtomicBool {
         AtomicBool { v: UnsafeCell::new(v as u8) }
     }
@@ -649,6 +650,7 @@ impl<T> AtomicPtr<T> {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_atomic_ptr_new"))]
     pub const fn new(p: *mut T) -> AtomicPtr<T> {
         AtomicPtr { p: UnsafeCell::new(p) }
     }
@@ -920,7 +922,7 @@ impl<T> AtomicPtr<T> {
 
 #[cfg(target_has_atomic = "ptr")]
 macro_rules! atomic_int {
-    ($stable:meta,
+    ($stable:meta, $const_unstable:meta,
      $stable_cxchg:meta,
      $stable_debug:meta,
      $stable_access:meta,
@@ -969,6 +971,7 @@ macro_rules! atomic_int {
             /// ```
             #[inline]
             #[$stable]
+            #[cfg_attr(not(stage0), $const_unstable)]
             pub const fn new(v: $int_type) -> Self {
                 $atomic_type {v: UnsafeCell::new(v)}
             }
@@ -1332,6 +1335,7 @@ macro_rules! atomic_int {
 #[cfg(target_has_atomic = "8")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_i8_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1340,6 +1344,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "8")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_u8_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1348,6 +1353,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "16")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_i16_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1356,6 +1362,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "16")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_u16_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1364,6 +1371,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "32")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_i32_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1372,6 +1380,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "32")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_u32_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1380,6 +1389,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "64")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_i64_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1388,6 +1398,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "64")]
 atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
+    rustc_const_unstable(feature = "const_atomic_u64_new"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
@@ -1396,6 +1407,7 @@ atomic_int! {
 #[cfg(target_has_atomic = "ptr")]
 atomic_int!{
     stable(feature = "rust1", since = "1.0.0"),
+    rustc_const_unstable(feature = "const_atomic_isize_new"),
     stable(feature = "extended_compare_and_swap", since = "1.10.0"),
     stable(feature = "atomic_debug", since = "1.3.0"),
     stable(feature = "atomic_access", since = "1.15.0"),
@@ -1404,6 +1416,7 @@ atomic_int!{
 #[cfg(target_has_atomic = "ptr")]
 atomic_int!{
     stable(feature = "rust1", since = "1.0.0"),
+    rustc_const_unstable(feature = "const_atomic_usize_new"),
     stable(feature = "extended_compare_and_swap", since = "1.10.0"),
     stable(feature = "atomic_debug", since = "1.3.0"),
     stable(feature = "atomic_access", since = "1.15.0"),

src/libcore/tests/lib.rs

@@ -11,7 +11,6 @@
 #![deny(warnings)]
 
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(core_float)]
 #![feature(core_private_bignum)]
 #![feature(core_private_diy_float)]
@@ -42,6 +41,10 @@
 #![feature(try_from)]
 #![feature(unique)]
 
+#![feature(const_atomic_bool_new)]
+#![feature(const_atomic_usize_new)]
+#![feature(const_atomic_isize_new)]
+
 extern crate core;
 extern crate test;
 extern crate rand;

src/librustc/ich/impls_syntax.rs

@@ -81,7 +81,12 @@ impl_stable_hash_for!(enum ::syntax::abi::Abi {
 });
 
 impl_stable_hash_for!(struct ::syntax::attr::Deprecation { since, note });
-impl_stable_hash_for!(struct ::syntax::attr::Stability { level, feature, rustc_depr });
+impl_stable_hash_for!(struct ::syntax::attr::Stability {
+    level,
+    feature,
+    rustc_depr,
+    rustc_const_unstable
+});
 
 impl<'a, 'gcx, 'tcx> HashStable<StableHashingContext<'a, 'gcx, 'tcx>>
 for ::syntax::attr::StabilityLevel {
@@ -102,6 +107,7 @@ for ::syntax::attr::StabilityLevel {
 }
 
 impl_stable_hash_for!(struct ::syntax::attr::RustcDeprecation { since, reason });
+impl_stable_hash_for!(struct ::syntax::attr::RustcConstUnstable { feature });
 
 
 impl_stable_hash_for!(enum ::syntax::attr::IntType {

src/librustc/lib.rs

@@ -22,7 +22,6 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(conservative_impl_trait)]
-#![feature(const_fn)]
 #![feature(core_intrinsics)]
 #![feature(i128_type)]
 #![cfg_attr(windows, feature(libc))]
@@ -36,6 +35,9 @@
 #![feature(trace_macros)]
 #![feature(test)]
 
+#![cfg_attr(stage0, feature(const_fn))]
+#![cfg_attr(not(stage0), feature(const_atomic_bool_new))]
+
 #![recursion_limit="256"]
 
 extern crate arena;

src/librustc/middle/stability.rs

@@ -427,6 +427,7 @@ impl<'a, 'tcx> Index<'tcx> {
                     },
                     feature: Symbol::intern("rustc_private"),
                     rustc_depr: None,
+                    rustc_const_unstable: None,
                 });
                 annotator.parent_stab = Some(stability);
             }

src/librustc_apfloat/lib.rs

@@ -45,11 +45,14 @@
 #![deny(warnings)]
 #![forbid(unsafe_code)]
 
-#![feature(const_fn)]
 #![feature(i128_type)]
 #![feature(slice_patterns)]
 #![feature(try_from)]
 
+#![cfg_attr(stage0, feature(const_fn))]
+#![cfg_attr(not(stage0), feature(const_min_value))]
+#![cfg_attr(not(stage0), feature(const_max_value))]
+
 #[macro_use]
 extern crate rustc_bitflags;
 

src/librustc_const_eval/lib.rs

@@ -23,9 +23,11 @@
 #![feature(slice_patterns)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(i128_type)]
 
+#![cfg_attr(stage0, feature(const_fn))]
+#![cfg_attr(not(stage0), feature(const_min_value))]
+
 extern crate arena;
 #[macro_use] extern crate syntax;
 #[macro_use] extern crate log;

src/librustc_const_math/lib.rs

@@ -19,10 +19,13 @@
       html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![deny(warnings)]
 
-#![feature(const_fn)]
 #![feature(i128)]
 #![feature(i128_type)]
 
+#![cfg_attr(stage0, feature(const_fn))]
+#![cfg_attr(not(stage0), feature(const_min_value))]
+#![cfg_attr(not(stage0), feature(const_max_value))]
+
 extern crate rustc_apfloat;
 
 extern crate syntax;

src/librustc_mir/diagnostics.rs

@@ -384,7 +384,7 @@ static B: &'static AtomicUsize = &A; // ok!
 You can also have this error while using a cell type:
 
 ```compile_fail,E0492
-#![feature(const_fn)]
+#![feature(const_cell_new)]
 
 use std::cell::Cell;
 
@@ -412,7 +412,7 @@ However, if you still wish to use these types, you can achieve this by an unsafe
 wrapper:
 
 ```
-#![feature(const_fn)]
+#![feature(const_cell_new)]
 
 use std::cell::Cell;
 use std::marker::Sync;

src/librustc_mir/transform/qualify_consts.rs

@@ -30,6 +30,7 @@ use rustc::mir::transform::{MirPass, MirSource};
 use rustc::mir::visit::{LvalueContext, Visitor};
 use rustc::middle::lang_items;
 use syntax::abi::Abi;
+use syntax::attr;
 use syntax::feature_gate::UnstableFeatures;
 use syntax_pos::{Span, DUMMY_SP};
 
@@ -713,14 +714,14 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
             self.visit_operand(func, location);
 
             let fn_ty = func.ty(self.mir, self.tcx);
-            let (mut is_shuffle, mut is_const_fn) = (false, false);
+            let (mut is_shuffle, mut is_const_fn) = (false, None);
             if let ty::TyFnDef(def_id, _) = fn_ty.sty {
                 match self.tcx.fn_sig(def_id).abi() {
                     Abi::RustIntrinsic |
                     Abi::PlatformIntrinsic => {
                         assert!(!self.tcx.is_const_fn(def_id));
                         match &self.tcx.item_name(def_id)[..] {
-                            "size_of" | "min_align_of" => is_const_fn = true,
+                            "size_of" | "min_align_of" => is_const_fn = Some(def_id),
 
                             name if name.starts_with("simd_shuffle") => {
                                 is_shuffle = true;
@@ -730,7 +731,9 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
                         }
                     }
                     _ => {
-                        is_const_fn = self.tcx.is_const_fn(def_id);
+                        if self.tcx.is_const_fn(def_id) {
+                            is_const_fn = Some(def_id);
+                        }
                     }
                 }
             }
@@ -751,25 +754,38 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
             }
 
             // Const fn calls.
-            if is_const_fn {
+            if let Some(def_id) = is_const_fn {
-                // We are in a const or static initializer,
+                // find corresponding rustc_const_unstable feature
-                if self.mode != Mode::Fn &&
+                if let Some(&attr::Stability {
+                    rustc_const_unstable: Some(attr::RustcConstUnstable {
+                        feature: ref feature_name
+                    }),
+                .. }) = self.tcx.lookup_stability(def_id) {
 
-                    // feature-gate is not enabled,
+                    // We are in a const or static initializer,
-                    !self.tcx.sess.features.borrow().const_fn &&
+                    if self.mode != Mode::Fn &&
 
-                    // this doesn't come from a crate with the feature-gate enabled,
+                        // feature-gate is not enabled,
-                    self.def_id.is_local() &&
+                        !self.tcx.sess.features.borrow()
+                            .declared_lib_features
+                            .iter()
+                            .any(|&(ref sym, _)| sym == feature_name) &&
 
-                    // this doesn't come from a macro that has #[allow_internal_unstable]
+                        // this doesn't come from a crate with the feature-gate enabled,
-                    !self.span.allows_unstable()
+                        self.def_id.is_local() &&
-                {
+
-                    let mut err = self.tcx.sess.struct_span_err(self.span,
+                        // this doesn't come from a macro that has #[allow_internal_unstable]
-                        "const fns are an unstable feature");
+                        !self.span.allows_unstable()
-                    help!(&mut err,
+                    {
-                          "in Nightly builds, add `#![feature(const_fn)]` \
+                        let mut err = self.tcx.sess.struct_span_err(self.span,
-                           to the crate attributes to enable");
+                            &format!("`{}` is not yet stable as a const fn",
-                    err.emit();
+                                     self.tcx.item_path_str(def_id)));
+                        help!(&mut err,
+                              "in Nightly builds, add `#![feature({})]` \
+                               to the crate attributes to enable",
+                              feature_name);
+                        err.emit();
+                    }
                 }
             } else {
                 self.qualif = Qualif::NOT_CONST;

src/librustc_trans/lib.rs

@@ -21,7 +21,6 @@
 
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
 #![feature(i128_type)]
@@ -31,6 +30,10 @@
 #![feature(slice_patterns)]
 #![feature(conservative_impl_trait)]
 
+#![cfg_attr(stage0, feature(const_fn))]
+#![cfg_attr(not(stage0), feature(const_atomic_bool_new))]
+#![cfg_attr(not(stage0), feature(const_once_new))]
+
 use rustc::dep_graph::WorkProduct;
 use syntax_pos::symbol::Symbol;
 

src/librustc_trans_utils/lib.rs

@@ -19,7 +19,6 @@
 
 #![feature(box_patterns)]
 #![feature(box_syntax)]
-#![feature(const_fn)]
 #![feature(custom_attribute)]
 #![allow(unused_attributes)]
 #![feature(i128_type)]
@@ -28,6 +27,8 @@
 #![feature(slice_patterns)]
 #![feature(conservative_impl_trait)]
 
+#![cfg_attr(stage0, feature(const_fn))]
+
 extern crate rustc;
 extern crate syntax;
 extern crate syntax_pos;

src/libstd/lib.rs

@@ -292,6 +292,7 @@
 #![feature(raw)]
 #![feature(repr_simd)]
 #![feature(rustc_attrs)]
+#![cfg_attr(not(stage0), feature(rustc_const_unstable))]
 #![feature(shared)]
 #![feature(sip_hash_13)]
 #![feature(slice_bytes)]
@@ -315,6 +316,17 @@
 #![feature(doc_cfg)]
 #![cfg_attr(test, feature(update_panic_count))]
 
+#![cfg_attr(not(stage0), feature(const_max_value))]
+#![cfg_attr(not(stage0), feature(const_atomic_bool_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_isize_new))]
+#![cfg_attr(not(stage0), feature(const_atomic_usize_new))]
+#![cfg_attr(all(not(stage0), windows), feature(const_atomic_ptr_new))]
+#![cfg_attr(not(stage0), feature(const_unsafe_cell_new))]
+#![cfg_attr(not(stage0), feature(const_cell_new))]
+#![cfg_attr(not(stage0), feature(const_once_new))]
+#![cfg_attr(not(stage0), feature(const_ptr_null))]
+#![cfg_attr(not(stage0), feature(const_ptr_null_mut))]
+
 #![default_lib_allocator]
 
 // Always use alloc_system during stage0 since we don't know if the alloc_*

src/libstd/sync/once.rs

@@ -156,6 +156,7 @@ struct Finish {
 impl Once {
     /// Creates a new `Once` value.
     #[stable(feature = "once_new", since = "1.2.0")]
+    #[cfg_attr(not(stage0), rustc_const_unstable(feature = "const_once_new"))]
     pub const fn new() -> Once {
         Once {
             state: AtomicUsize::new(INCOMPLETE),

src/libsyntax/attr.rs

@@ -637,12 +637,13 @@ pub fn eval_condition<F>(cfg: &ast::MetaItem, sess: &ParseSess, eval: &mut F)
     }
 }
 
-/// Represents the #[stable], #[unstable] and #[rustc_deprecated] attributes.
+/// Represents the #[stable], #[unstable], #[rustc_{deprecated,const_unstable}] attributes.
 #[derive(RustcEncodable, RustcDecodable, Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Stability {
     pub level: StabilityLevel,
     pub feature: Symbol,
     pub rustc_depr: Option<RustcDeprecation>,
+    pub rustc_const_unstable: Option<RustcConstUnstable>,
 }
 
 /// The available stability levels.
@@ -659,6 +660,11 @@ pub struct RustcDeprecation {
     pub reason: Symbol,
 }
 
+#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Debug, Eq, Hash)]
+pub struct RustcConstUnstable {
+    pub feature: Symbol,
+}
+
 #[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Debug, Eq, Hash)]
 pub struct Deprecation {
     pub since: Option<Symbol>,
@@ -678,9 +684,15 @@ fn find_stability_generic<'a, I>(diagnostic: &Handler,
 {
     let mut stab: Option<Stability> = None;
     let mut rustc_depr: Option<RustcDeprecation> = None;
+    let mut rustc_const_unstable: Option<RustcConstUnstable> = None;
 
     'outer: for attr in attrs_iter {
-        if attr.path != "rustc_deprecated" && attr.path != "unstable" && attr.path != "stable" {
+        if ![
+            "rustc_deprecated",
+            "rustc_const_unstable",
+            "unstable",
+            "stable",
+        ].iter().any(|&s| attr.path == s) {
             continue // not a stability level
         }
 
@@ -703,21 +715,18 @@ fn find_stability_generic<'a, I>(diagnostic: &Handler,
                 }
             };
 
-            match &*meta.name.as_str() {
+            macro_rules! get_meta {
-                "rustc_deprecated" => {
+                ($($name:ident),+) => {
-                    if rustc_depr.is_some() {
+                    $(
-                        span_err!(diagnostic, item_sp, E0540,
+                        let mut $name = None;
-                                  "multiple rustc_deprecated attributes");
+                    )+
-                        break
-                    }
-
-                    let mut since = None;
-                    let mut reason = None;
                     for meta in metas {
                         if let Some(mi) = meta.meta_item() {
                             match &*mi.name().as_str() {
-                                "since" => if !get(mi, &mut since) { continue 'outer },
+                                $(
-                                "reason" => if !get(mi, &mut reason) { continue 'outer },
+                                    stringify!($name)
+                                        => if !get(mi, &mut $name) { continue 'outer },
+                                )+
                                 _ => {
                                     handle_errors(diagnostic, mi.span,
                                                   AttrError::UnknownMetaItem(mi.name()));
@@ -729,6 +738,18 @@ fn find_stability_generic<'a, I>(diagnostic: &Handler,
                             continue 'outer
                         }
                     }
+                }
+            }
+
+            match &*meta.name.as_str() {
+                "rustc_deprecated" => {
+                    if rustc_depr.is_some() {
+                        span_err!(diagnostic, item_sp, E0540,
+                                  "multiple rustc_deprecated attributes");
+                        continue 'outer
+                    }
+
+                    get_meta!(since, reason);
 
                     match (since, reason) {
                         (Some(since), Some(reason)) => {
@@ -747,6 +768,23 @@ fn find_stability_generic<'a, I>(diagnostic: &Handler,
                         }
                     }
                 }
+                "rustc_const_unstable" => {
+                    if rustc_const_unstable.is_some() {
+                        span_err!(diagnostic, item_sp, E0553,
+                                  "multiple rustc_const_unstable attributes");
+                        continue 'outer
+                    }
+
+                    get_meta!(feature);
+                    if let Some(feature) = feature {
+                        rustc_const_unstable = Some(RustcConstUnstable {
+                            feature
+                        });
+                    } else {
+                        span_err!(diagnostic, attr.span(), E0629, "missing 'feature'");
+                        continue
+                    }
+                }
                 "unstable" => {
                     if stab.is_some() {
                         handle_errors(diagnostic, attr.span(), AttrError::MultipleStabilityLevels);
@@ -791,6 +829,7 @@ fn find_stability_generic<'a, I>(diagnostic: &Handler,
                                 },
                                 feature,
                                 rustc_depr: None,
+                                rustc_const_unstable: None,
                             })
                         }
                         (None, _, _) => {
@@ -836,6 +875,7 @@ fn find_stability_generic<'a, I>(diagnostic: &Handler,
                                 },
                                 feature,
                                 rustc_depr: None,
+                                rustc_const_unstable: None,
                             })
                         }
                         (None, _) => {
@@ -867,6 +907,17 @@ fn find_stability_generic<'a, I>(diagnostic: &Handler,
         }
     }
 
+    // Merge the const-unstable info into the stability info
+    if let Some(rustc_const_unstable) = rustc_const_unstable {
+        if let Some(ref mut stab) = stab {
+            stab.rustc_const_unstable = Some(rustc_const_unstable);
+        } else {
+            span_err!(diagnostic, item_sp, E0630,
+                      "rustc_const_unstable attribute must be paired with \
+                       either stable or unstable attribute");
+        }
+    }
+
     stab
 }
 

src/libsyntax/diagnostic_list.rs

@@ -357,8 +357,11 @@ register_diagnostics! {
     E0549, // rustc_deprecated attribute must be paired with either stable or unstable attribute
     E0550, // multiple deprecated attributes
     E0551, // incorrect meta item
+    E0553, // multiple rustc_const_unstable attributes
     E0555, // malformed feature attribute, expected #![feature(...)]
     E0556, // malformed feature, expected just one word
     E0584, // file for module `..` found at both .. and ..
     E0589, // invalid `repr(align)` attribute
+    E0629, // missing 'feature' (rustc_const_unstable)
+    E0630, // rustc_const_unstable attribute must be paired with stable/unstable attribute
 }

src/libsyntax/feature_gate.rs

@@ -137,6 +137,7 @@ declare_features! (
 
     // rustc internal
     (active, rustc_diagnostic_macros, "1.0.0", None),
+    (active, rustc_const_unstable, "1.0.0", None),
     (active, advanced_slice_patterns, "1.0.0", Some(23121)),
     (active, box_syntax, "1.0.0", Some(27779)),
     (active, placement_in_syntax, "1.0.0", Some(27779)),
@@ -622,6 +623,11 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                              "the `#[rustc_on_unimplemented]` attribute \
                                               is an experimental feature",
                                              cfg_fn!(on_unimplemented))),
+    ("rustc_const_unstable", Normal, Gated(Stability::Unstable,
+                                             "rustc_const_unstable",
+                                             "the `#[rustc_const_unstable]` attribute \
+                                              is an internal feature",
+                                             cfg_fn!(rustc_const_unstable))),
     ("global_allocator", Normal, Gated(Stability::Unstable,
                                        "global_allocator",
                                        "the `#[global_allocator]` attribute is \

src/test/compile-fail-fulldeps/dropck_tarena_cycle_checked.rs

@@ -16,7 +16,8 @@
 //  which is a reduction of this code to more directly show the reason
 //  for the error message we see here.)
 
-#![feature(const_fn, rustc_private)]
+#![feature(rustc_private)]
+#![feature(const_atomic_usize_new)]
 
 extern crate arena;
 

src/test/compile-fail/const-call.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(const_fn)]
-
 fn f(x: usize) -> usize {
     x
 }

src/test/compile-fail/const-fn-feature-flags.rs

@@ -0,0 +1,24 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test use of const fns in std using individual feature gates.
+
+use std::cell::Cell;
+
+const CELL: Cell<i32> = Cell::new(42); //~ERROR not yet stable as a const fn
+    //~^HELP #![feature(const_cell_new)]
+
+fn main() {
+    let v = CELL.get();
+    CELL.set(v+1);
+
+    assert_eq!(CELL.get(), v);
+}
+

src/test/compile-fail/dropck_trait_cycle_checked.rs

@@ -13,7 +13,7 @@
 //
 // (Compare against compile-fail/dropck_vec_cycle_checked.rs)
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::cell::Cell;
 use id::Id;

src/test/compile-fail/feature-gate-rustc_const_unstable.rs

@@ -8,19 +8,16 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// aux-build:const_fn_lib.rs
+// Test internal const fn feature gate.
-
-// A very basic test of const fn functionality.
 
+#![feature(staged_api)]
 #![feature(const_fn)]
+//#![feature(rustc_const_unstable)]
 
-extern crate const_fn_lib;
+#[stable(feature="zing", since="1.0.0")]
-
+#[rustc_const_unstable(feature="fzzzzzt")] //~ERROR internal feature
-use const_fn_lib::foo;
+pub const fn bazinga() {}
-
-const FOO: usize = foo();
 
 fn main() {
-    assert_eq!(FOO, 22);
-    let _: [i32; foo()] = [42; 22];
 }
+

src/test/compile-fail/functional-struct-update-respects-privacy.rs

@@ -10,8 +10,6 @@
 
 // RFC 736 (and Issue 21407): functional struct update should respect privacy.
 
-#![feature(const_fn)]
-
 // The `foo` module attempts to maintains an invariant that each `S`
 // has a unique `u64` id.
 use self::foo::S;

src/test/compile-fail/issue-17718-const-borrow.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(const_fn)]
+#![feature(const_unsafe_cell_new)]
 
 use std::cell::UnsafeCell;
 

src/test/compile-fail/issue-43733-2.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(const_fn)]
+#![feature(const_fn, const_cell_new, const_unsafe_cell_new)]
 #![feature(cfg_target_thread_local, thread_local_internals)]
 
 // On platforms *without* `#[thread_local]`, use

src/test/compile-fail/issue-7364.rs

@@ -8,9 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(box_syntax)]
+#![feature(box_syntax, const_refcell_new)]
-#![feature(const_fn)]
-#![allow(warnings)]
 
 use std::cell::RefCell;
 
@@ -18,5 +16,6 @@ use std::cell::RefCell;
 static boxed: Box<RefCell<isize>> = box RefCell::new(0);
 //~^ ERROR allocations are not allowed in statics
 //~| ERROR `std::cell::RefCell<isize>: std::marker::Sync` is not satisfied
+//~| WARN unsupported constant expr
 
 fn main() { }

src/test/compile-fail/stability-attribute-sanity.rs

@@ -10,7 +10,7 @@
 
 // Various checks that stability attributes are used correctly, per RFC 507
 
-#![feature(staged_api)]
+#![feature(const_fn, staged_api, rustc_const_unstable)]
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
@@ -88,8 +88,11 @@ fn multiple3() { }
 #[stable(feature = "a", since = "b")]
 #[rustc_deprecated(since = "b", reason = "text")]
 #[rustc_deprecated(since = "b", reason = "text")]
-fn multiple4() { } //~ ERROR multiple rustc_deprecated attributes [E0540]
+#[rustc_const_unstable(feature = "a")]
+#[rustc_const_unstable(feature = "b")]
+pub const fn multiple4() { } //~ ERROR multiple rustc_deprecated attributes [E0540]
 //~^ ERROR Invalid stability or deprecation version found
+//~| ERROR multiple rustc_const_unstable attributes
 
 #[rustc_deprecated(since = "a", reason = "text")]
 fn deprecated_without_unstable_or_stable() { }

src/test/debuginfo/constant-debug-locs.rs

@@ -15,7 +15,7 @@
 #![allow(dead_code, unused_variables)]
 #![feature(omit_gdb_pretty_printer_section)]
 #![omit_gdb_pretty_printer_section]
-#![feature(const_fn)]
+#![feature(const_unsafe_cell_new)]
 #![feature(static_mutex)]
 
 // This test makes sure that the compiler doesn't crash when trying to assign

src/test/run-pass-valgrind/cast-enum-with-dtor.rs

@@ -11,7 +11,7 @@
 // no-prefer-dynamic
 
 #![allow(dead_code)]
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 // check dtor calling order when casting enums.
 

src/test/run-pass/associated-types-project-from-type-param-via-bound-in-where-clause.rs

@@ -12,7 +12,7 @@
 // `Item` originates in a where-clause, not the declaration of
 // `T`. Issue #20300.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::marker::{PhantomData};
 use std::sync::atomic::{AtomicUsize};

src/test/run-pass/auxiliary/const_fn_lib.rs

@@ -13,4 +13,4 @@
 #![crate_type="rlib"]
 #![feature(const_fn)]
 
-pub const fn foo() -> usize { 22 } //~ ERROR const fn is unstable
+pub const fn foo() -> usize { 22 }

src/test/run-pass/auxiliary/issue-17718-aux.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::sync::atomic;
 

src/test/run-pass/auxiliary/thread-local-extern-static.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(cfg_target_thread_local, const_fn, thread_local)]
+#![feature(const_cell_new)]
 #![crate_type = "lib"]
 
 #[cfg(target_thread_local)]

src/test/run-pass/box-of-array-of-drop-1.rs

@@ -13,7 +13,7 @@
 
 // ignore-emscripten no threads support
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};

src/test/run-pass/box-of-array-of-drop-2.rs

@@ -13,7 +13,7 @@
 
 // ignore-emscripten no threads support
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};

src/test/run-pass/const-fn-feature-flags.rs

@@ -0,0 +1,25 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test use of const fns in std using individual feature gates.
+
+#![feature(const_cell_new)]
+
+use std::cell::Cell;
+
+const CELL: Cell<i32> = Cell::new(42);
+
+fn main() {
+    let v = CELL.get();
+    CELL.set(v+1);
+
+    assert_eq!(CELL.get(), v);
+}
+

src/test/run-pass/const-fn-stability-calls.rs

@@ -16,8 +16,8 @@ extern crate const_fn_lib;
 
 use const_fn_lib::foo;
 
-static FOO: usize = foo(); //~ ERROR const fns are an unstable feature
+static FOO: usize = foo();
-const BAR: usize = foo(); //~ ERROR const fns are an unstable feature
+const BAR: usize = foo();
 
 macro_rules! constant {
     ($n:ident: $t:ty = $v:expr) => {
@@ -26,9 +26,9 @@ macro_rules! constant {
 }
 
 constant! {
-    BAZ: usize = foo() //~ ERROR const fns are an unstable feature
+    BAZ: usize = foo()
 }
 
 fn main() {
-//    let x: [usize; foo()] = [];
+    let x: [usize; foo()] = [42; foo()];
 }

src/test/run-pass/const-size_of-align_of.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(const_fn)]
+#![feature(const_fn, const_size_of, const_align_of)]
 
 use std::mem;
 

src/test/run-pass/issue-17718-static-unsafe-interior.rs

@@ -11,8 +11,7 @@
 // pretty-expanded FIXME #23616
 
 #![feature(core)]
-#![feature(const_fn)]
+#![feature(const_unsafe_cell_new)]
-
 
 use std::marker;
 use std::cell::UnsafeCell;

src/test/run-pass/issue-17718.rs

@@ -12,7 +12,7 @@
 
 
 #![feature(core)]
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 extern crate issue_17718_aux as other;
 

src/test/run-pass/issue-21486.rs

@@ -12,7 +12,7 @@
 // created via FRU and control-flow breaks in the middle of
 // construction.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::sync::atomic::{Ordering, AtomicUsize};
 

src/test/run-pass/issue-26655.rs

@@ -10,10 +10,10 @@
 
 // ignore-emscripten no threads support
 
-#![feature(const_fn)]
-
 // Check that the destructors of simple enums are run on unwinding
 
+#![feature(const_atomic_usize_new)]
+
 use std::sync::atomic::{Ordering, AtomicUsize};
 use std::thread;
 

src/test/run-pass/issue-27997.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::sync::atomic::{Ordering, AtomicUsize};
 

src/test/run-pass/nested-vec-3.rs

@@ -14,7 +14,7 @@
 // the contents implement Drop and we hit a panic in the middle of
 // construction.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};

src/test/run-pass/panic-handler-chain.rs

@@ -10,7 +10,8 @@
 
 // ignore-emscripten no threads support
 
-#![feature(panic_handler, const_fn, std_panic)]
+#![feature(panic_handler, std_panic)]
+#![feature(const_atomic_usize_new)]
 
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::panic;

src/test/run-pass/panic-handler-set-twice.rs

@@ -7,7 +7,8 @@
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
-#![feature(panic_handler, const_fn, std_panic)]
+#![feature(panic_handler, std_panic)]
+#![feature(const_atomic_usize_new)]
 
 // ignore-emscripten no threads support
 

src/test/run-pass/struct-order-of-eval-3.rs

@@ -11,7 +11,7 @@
 // Checks that functional-record-update order-of-eval is as expected
 // even when no Drop-implementations are involved.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::sync::atomic::{Ordering, AtomicUsize};
 

src/test/run-pass/struct-order-of-eval-4.rs

@@ -11,7 +11,7 @@
 // Checks that struct-literal expression order-of-eval is as expected
 // even when no Drop-implementations are involved.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::sync::atomic::{Ordering, AtomicUsize};
 

src/test/run-pass/vector-sort-panic-safe.rs

@@ -10,9 +10,9 @@
 
 // ignore-emscripten no threads support
 
-#![feature(const_fn)]
 #![feature(rand)]
 #![feature(sort_unstable)]
+#![feature(const_atomic_usize_new)]
 
 use std::__rand::{thread_rng, Rng};
 use std::cell::Cell;

src/test/ui/span/dropck_arr_cycle_checked.rs

@@ -13,7 +13,7 @@
 //
 // (Compare against compile-fail/dropck_vec_cycle_checked.rs)
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::cell::Cell;
 use id::Id;

src/test/ui/span/dropck_vec_cycle_checked.rs

@@ -12,7 +12,7 @@
 //
 // (Compare against compile-fail/dropck_arr_cycle_checked.rs)
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::cell::Cell;
 use id::Id;

src/test/ui/span/vec-must-not-hide-type-from-dropck.rs

@@ -23,7 +23,7 @@
 // conditions above to be satisfied, meaning that if the dropck is
 // sound, it should reject this code.
 
-#![feature(const_fn)]
+#![feature(const_atomic_usize_new)]
 
 use std::cell::Cell;
 use id::Id;

src/tools/rls

@@ -1 +1 @@
-Subproject commit 8dd70945fb049df3f9dc7685cdc58d94e05e8ffc
+Subproject commit 52d48656f93eeeb2c568e6c1048e64168e5b209f