add static_in_const feature gate

src/doc/reference.md

@@ -2441,6 +2441,9 @@ The currently implemented features of the reference compiler are:
             into a Rust program. This capability, especially the signature for the
             annotated function, is subject to change.
 
+* `static_in_const` - Enables lifetime elision with a `'static` default for
+                      `const` and `static` item declarations.
+
 * `thread_local` - The usage of the `#[thread_local]` attribute is experimental
                    and should be seen as unstable. This attribute is used to
                    declare a `static` as being unique per-thread leveraging

src/librustc_typeck/collect.rs

@@ -1567,7 +1567,7 @@ fn type_of_def_id<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
             NodeItem(item) => {
                 match item.node {
                     ItemStatic(ref t, ..) | ItemConst(ref t, _) => {
-                        ccx.icx(&()).to_ty(&ElidableRscope::new(ty::ReStatic), &t)
+                        ccx.icx(&()).to_ty(&StaticRscope::new(&ccx.tcx), &t)
                     }
                     ItemFn(ref decl, unsafety, _, abi, ref generics, _) => {
                         let tofd = AstConv::ty_of_bare_fn(&ccx.icx(generics), unsafety, abi, &decl,

src/librustc_typeck/rscope.rs

@@ -213,6 +213,45 @@ impl RegionScope for ElidableRscope {
     }
 }
 
+/// A scope that behaves as an ElidabeRscope with a `'static` default region
+/// that should also warn if the `static_in_const` feature is unset.
+#[derive(Copy, Clone)]
+pub struct StaticRscope<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
+    tcx: &'a ty::TyCtxt<'a, 'gcx, 'tcx>,
+}
+
+impl<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> StaticRscope<'a, 'gcx, 'tcx> {
+    /// create a new StaticRscope from a reference to the `TyCtxt`
+    pub fn new(tcx: &'a ty::TyCtxt<'a, 'gcx, 'tcx>) -> Self {
+        StaticRscope { tcx: tcx }
+    }
+}
+
+impl<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> RegionScope for StaticRscope<'a, 'gcx, 'tcx> {
+    fn anon_regions(&self,
+                    span: Span,
+                    count: usize)
+                    -> Result<Vec<ty::Region>, Option<Vec<ElisionFailureInfo>>> {
+        if !self.tcx.sess.features.borrow().static_in_const {
+            self.tcx
+                .sess
+                .struct_span_err(span,
+                                 "this needs a `'static` lifetime or the \
+                                 `static_in_const` feature, see #35897")
+                .emit();
+        }
+        Ok(vec![ty::ReStatic; count])
+    }
+
+    fn object_lifetime_default(&self, span: Span) -> Option<ty::Region> {
+        Some(self.base_object_lifetime_default(span))
+    }
+
+    fn base_object_lifetime_default(&self, _span: Span) -> ty::Region {
+        ty::ReStatic
+    }
+}
+
 /// A scope in which we generate anonymous, late-bound regions for
 /// omitted regions. This occurs in function signatures.
 pub struct BindingRscope {

src/libsyntax/feature_gate.rs

@@ -295,6 +295,9 @@ declare_features! (
 
     // Allows untagged unions `union U { ... }`
     (active, untagged_unions, "1.13.0", Some(32836)),
+
+    // elide `'static` lifetimes in `static`s and `const`s
+    (active, static_in_const, "1.13.0", Some(35897)),
 );
 
 declare_features! (

src/test/compile-fail/feature-gate-static-in-const.rs

@@ -0,0 +1,14 @@
+// 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.
+
+static FOO: &str = "this will work once static_in_const is stable";
+//~^ ERROR: this needs a `'static` lifetime or the `static_in_const` feature
+
+fn main() {}

src/test/compile-fail/issue-24446.rs

@@ -12,7 +12,6 @@ fn main() {
     static foo: Fn() -> u32 = || -> u32 {
         //~^ ERROR: mismatched types
         //~| ERROR: `std::ops::Fn() -> u32 + 'static: std::marker::Sized` is not satisfied
-
         0
     };
 }

src/test/compile-fail/rfc1623.rs

@@ -7,7 +7,7 @@
 // <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(static_in_const)]
 #![allow(dead_code)]
 
 fn non_elidable<'a, 'b>(a: &'a u8, b: &'b u8) -> &'a u8 {

src/test/run-pass/rfc1623.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(static_in_const)]
 #![allow(dead_code)]
 
 // very simple test for a 'static static with default lifetime