Auto merge of #21744 - eddyb:rvalue-promotion, r=nikomatsakis

This includes everything necessary for promoting borrows of constant rvalues to `'static`.
That is, `&expr` will have the type `&'static T` if `const T: &'static T = &expr;` is valid.
There is a small exception, dereferences of raw pointers, as they misbehave.
They still "work" in constants as I didn't want to break legitimate uses (are there any?).

The qualification done here can be expanded to allow simple CTFE via `const fn`.

Author: bors

src/librand/reseeding.rs

@@ -134,7 +134,11 @@ pub trait Reseeder<R> {
 /// Reseed an RNG using a `Default` instance. This reseeds by
 /// replacing the RNG with the result of a `Default::default` call.
 #[derive(Copy)]
-pub struct ReseedWithDefault;
+pub struct ReseedWithDefault { __hack: [u8; 0] }
+// FIXME(#21721) used to be an unit struct but that can cause
+// certain LLVM versions to abort during optimizations.
+#[allow(non_upper_case_globals)]
+pub const ReseedWithDefault: ReseedWithDefault = ReseedWithDefault { __hack: [] };
 
 impl<R: Rng + Default> Reseeder<R> for ReseedWithDefault {
     fn reseed(&mut self, rng: &mut R) {

src/librustc/diagnostics.rs

@@ -59,6 +59,7 @@ register_diagnostics! {
     E0010,
     E0011,
     E0012,
+    E0013,
     E0014,
     E0015,
     E0016,

src/librustc/lib.rs

@@ -90,7 +90,6 @@ pub mod middle {
     pub mod check_loop;
     pub mod check_match;
     pub mod check_rvalues;
-    pub mod check_static;
     pub mod const_eval;
     pub mod dataflow;
     pub mod dead;

src/librustc/lint/builtin.rs

@@ -199,7 +199,7 @@ impl LintPass for TypeLimits {
                             if let ast::LitInt(shift, _) = lit.node { shift >= bits }
                             else { false }
                         } else {
-                            match eval_const_expr_partial(cx.tcx, &**r) {
+                            match eval_const_expr_partial(cx.tcx, &**r, Some(cx.tcx.types.uint)) {
                                 Ok(const_int(shift)) => { shift as u64 >= bits },
                                 Ok(const_uint(shift)) => { shift >= bits },
                                 _ => { false }

src/librustc/metadata/common.rs

@@ -12,7 +12,6 @@
 
 pub use self::astencode_tag::*;
 
-use std::mem;
 use back::svh::Svh;
 
 // EBML enum definitions and utils shared by the encoder and decoder
@@ -113,7 +112,7 @@ pub const tag_items_data_item_reexport_def_id: uint = 0x39;
 pub const tag_items_data_item_reexport_name: uint = 0x3a;
 
 // used to encode crate_ctxt side tables
-#[derive(Copy, PartialEq)]
+#[derive(Copy, PartialEq, FromPrimitive)]
 #[repr(uint)]
 pub enum astencode_tag { // Reserves 0x40 -- 0x5f
     tag_ast = 0x40,
@@ -144,17 +143,7 @@ pub enum astencode_tag { // Reserves 0x40 -- 0x5f
     tag_table_upvar_capture_map = 0x56,
     tag_table_capture_modes = 0x57,
     tag_table_object_cast_map = 0x58,
-}
-
-static first_astencode_tag: uint = tag_ast as uint;
-static last_astencode_tag: uint = tag_table_object_cast_map as uint;
-impl astencode_tag {
-    pub fn from_uint(value : uint) -> Option<astencode_tag> {
-        let is_a_tag = first_astencode_tag <= value && value <= last_astencode_tag;
-        if !is_a_tag { None } else {
-            Some(unsafe { mem::transmute::<uint, astencode_tag>(value) })
-        }
-    }
+    tag_table_const_qualif = 0x59,
 }
 
 pub const tag_item_trait_item_sort: uint = 0x60;

src/librustc/middle/astencode.rs

@@ -23,6 +23,7 @@ use metadata::tydecode;
 use metadata::tydecode::{DefIdSource, NominalType, TypeWithId, TypeParameter};
 use metadata::tydecode::{RegionParameter, ClosureSource};
 use metadata::tyencode;
+use middle::check_const::ConstQualif;
 use middle::mem_categorization::Typer;
 use middle::subst;
 use middle::subst::VecPerParamSpace;
@@ -38,6 +39,7 @@ use syntax::ptr::P;
 use syntax;
 
 use std::old_io::Seek;
+use std::num::FromPrimitive;
 use std::rc::Rc;
 
 use rbml::io::SeekableMemWriter;
@@ -1305,6 +1307,15 @@ fn encode_side_tables_for_id(ecx: &e::EncodeContext,
             })
         })
     }
+
+    for &qualif in tcx.const_qualif_map.borrow().get(&id).iter() {
+        rbml_w.tag(c::tag_table_const_qualif, |rbml_w| {
+            rbml_w.id(id);
+            rbml_w.tag(c::tag_table_val, |rbml_w| {
+                qualif.encode(rbml_w).unwrap()
+            })
+        })
+    }
 }
 
 trait doc_decoder_helpers {
@@ -1836,8 +1847,8 @@ fn decode_side_tables(dcx: &DecodeContext,
         debug!(">> Side table document with tag 0x{:x} \
                 found for id {} (orig {})",
                tag, id, id0);
-
-        match c::astencode_tag::from_uint(tag) {
+        let decoded_tag: Option<c::astencode_tag> = FromPrimitive::from_uint(tag);
+        match decoded_tag {
             None => {
                 dcx.tcx.sess.bug(
                     &format!("unknown tag found in side tables: {:x}",
@@ -1919,6 +1930,10 @@ fn decode_side_tables(dcx: &DecodeContext,
                         dcx.tcx.closure_kinds.borrow_mut().insert(ast_util::local_def(id),
                                                                   closure_kind);
                     }
+                    c::tag_table_const_qualif => {
+                        let qualif: ConstQualif = Decodable::decode(val_dsr).unwrap();
+                        dcx.tcx.const_qualif_map.borrow_mut().insert(id, qualif);
+                    }
                     _ => {
                         dcx.tcx.sess.bug(
                             &format!("unknown tag found in side tables: {:x}",