Constants reading or referencing statics is illegal

and some uses of it will be illegal forever
(e.g. mutable or interior mutable statics)

Author: oli-obk

src/librustc_mir/const_eval.rs

@@ -182,6 +182,7 @@ fn eval_body_using_ecx<'mir, 'tcx>(
 #[derive(Clone, Debug)]
 pub enum ConstEvalError {
     NeedsRfc(String),
+    ConstAccessesStatic,
 }
 
 impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalError {
@@ -201,6 +202,7 @@ impl fmt::Display for ConstEvalError {
                     msg
                 )
             }
+            ConstAccessesStatic => write!(f, "constant accesses static"),
         }
     }
 }
@@ -210,6 +212,7 @@ impl Error for ConstEvalError {
         use self::ConstEvalError::*;
         match *self {
             NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
+            ConstAccessesStatic => "constant accesses static",
         }
     }
 
@@ -547,9 +550,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         if memory_extra.can_access_statics {
             Ok(())
         } else {
-            Err(ConstEvalError::NeedsRfc(
-                "constants accessing static items".to_string(),
-            ).into())
+            Err(ConstEvalError::ConstAccessesStatic.into())
         }
     }
 }

src/test/ui/consts/const-points-to-static.stderr

@@ -8,7 +8,7 @@ error[E0080]: it is undefined behavior to use this value
   --> $DIR/const-points-to-static.rs:5:1
    |
 LL | const TEST: &u8 = &MY_STATIC;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ "constants accessing static items" needs an rfc before being allowed inside constants
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constant accesses static
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
 

src/test/ui/consts/const-prop-read-static-in-const.stderr

@@ -10,7 +10,7 @@ error: any use of this value will cause an error
 LL | const TEST: u8 = MY_STATIC;
    | -----------------^^^^^^^^^-
    |                  |
-   |                  "constants accessing static items" needs an rfc before being allowed inside constants
+   |                  constant accesses static
    |
    = note: `#[deny(const_err)]` on by default
 

src/test/ui/consts/miri_unleashed/const_refers_to_static.stderr

@@ -42,7 +42,7 @@ LL | |     static FOO: AtomicUsize = AtomicUsize::new(0);
 LL | |     unsafe { &*(&FOO as *const _ as *const usize) }
 LL | |
 LL | | };
-   | |__^ "constants accessing static items" needs an rfc before being allowed inside constants
+   | |__^ constant accesses static
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
 
@@ -54,7 +54,7 @@ LL | |     static FOO: usize = 0;
 LL | |     &FOO
 LL | |
 LL | | };
-   | |__^ "constants accessing static items" needs an rfc before being allowed inside constants
+   | |__^ constant accesses static
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
 

src/test/ui/issues/issue-52060.stderr

@@ -8,7 +8,7 @@ error[E0080]: evaluation of constant value failed
   --> $DIR/issue-52060.rs:4:26
    |
 LL | static B: [u32; 1] = [0; A.len()];
-   |                          ^ "constants accessing static items" needs an rfc before being allowed inside constants
+   |                          ^ constant accesses static
 
 error: aborting due to 2 previous errors