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`.

2 files changed, 32 insertions, 31 deletions

diff --git a/src/test/debuginfo/basic-types-globals-metadata.rs b/src/test/debuginfo/basic-types-globals-metadata.rs
index e9f801c5f05..91e78c820e6 100644
--- a/src/test/debuginfo/basic-types-globals-metadata.rs
+++ b/src/test/debuginfo/basic-types-globals-metadata.rs
@@ -47,26 +47,26 @@
 #![allow(dead_code)]
 #![omit_gdb_pretty_printer_section]
 
-
-static B: bool = false;
-static I: int = -1;
-static C: char = 'a';
-static I8: i8 = 68;
-static I16: i16 = -16;
-static I32: i32 = -32;
-static I64: i64 = -64;
-static U: uint = 1;
-static U8: u8 = 100;
-static U16: u16 = 16;
-static U32: u32 = 32;
-static U64: u64 = 64;
-static F32: f32 = 2.5;
-static F64: f64 = 3.5;
+// N.B. These are `mut` only so they don't constant fold away.
+static mut B: bool = false;
+static mut I: int = -1;
+static mut C: char = 'a';
+static mut I8: i8 = 68;
+static mut I16: i16 = -16;
+static mut I32: i32 = -32;
+static mut I64: i64 = -64;
+static mut U: uint = 1;
+static mut U8: u8 = 100;
+static mut U16: u16 = 16;
+static mut U32: u32 = 32;
+static mut U64: u64 = 64;
+static mut F32: f32 = 2.5;
+static mut F64: f64 = 3.5;
 
 fn main() {
     _zzz(); // #break
 
-    let a = (B, I, C, I8, I16, I32, I64, U, U8, U16, U32, U64, F32, F64);
+    let a = unsafe { (B, I, C, I8, I16, I32, I64, U, U8, U16, U32, U64, F32, F64) };
 }
 
 fn _zzz() {()}
diff --git a/src/test/debuginfo/basic-types-globals.rs b/src/test/debuginfo/basic-types-globals.rs
index a4d4ddfea53..d37b0f60d3d 100644
--- a/src/test/debuginfo/basic-types-globals.rs
+++ b/src/test/debuginfo/basic-types-globals.rs
@@ -52,25 +52,26 @@
 #![allow(unused_variables)]
 #![omit_gdb_pretty_printer_section]
 
-static B: bool = false;
-static I: int = -1;
-static C: char = 'a';
-static I8: i8 = 68;
-static I16: i16 = -16;
-static I32: i32 = -32;
-static I64: i64 = -64;
-static U: uint = 1;
-static U8: u8 = 100;
-static U16: u16 = 16;
-static U32: u32 = 32;
-static U64: u64 = 64;
-static F32: f32 = 2.5;
-static F64: f64 = 3.5;
+// N.B. These are `mut` only so they don't constant fold away.
+static mut B: bool = false;
+static mut I: int = -1;
+static mut C: char = 'a';
+static mut I8: i8 = 68;
+static mut I16: i16 = -16;
+static mut I32: i32 = -32;
+static mut I64: i64 = -64;
+static mut U: uint = 1;
+static mut U8: u8 = 100;
+static mut U16: u16 = 16;
+static mut U32: u32 = 32;
+static mut U64: u64 = 64;
+static mut F32: f32 = 2.5;
+static mut F64: f64 = 3.5;
 
 fn main() {
     _zzz(); // #break
 
-    let a = (B, I, C, I8, I16, I32, I64, U, U8, U16, U32, U64, F32, F64);
+    let a = unsafe { (B, I, C, I8, I16, I32, I64, U, U8, U16, U32, U64, F32, F64) };
 }
 
 fn _zzz() {()}