do not use InterpError::description outside librustc::mir

Author: RalfJung

src/librustc/mir/interpret/error.rs

@@ -330,7 +330,7 @@ pub enum InterpError<'tcx, O> {
 pub type InterpResult<'tcx, T = ()> = Result<T, InterpErrorInfo<'tcx>>;
 
 impl<'tcx, O> InterpError<'tcx, O> {
-    pub fn description(&self) -> &str {
+    pub(crate) fn description(&self) -> &str {
         use self::InterpError::*;
         match *self {
             MachineError(ref inner) => inner,

src/librustc_codegen_ssa/mir/block.rs

@@ -418,8 +418,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     vec![file_line_col, index, len])
             }
             _ => {
-                let str = msg.description();
-                let msg_str = LocalInternedString::intern(str);
+                let str = format!("{:?}", msg);
+                let msg_str = LocalInternedString::intern(&str);
                 let msg_file_line_col = bx.static_panic_msg(
                     Some(msg_str),
                     filename,

src/librustc_mir/transform/const_prop.rs

@@ -809,7 +809,7 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
         self.super_terminator(terminator, location);
         let source_info = terminator.source_info;
         match &mut terminator.kind {
-            TerminatorKind::Assert { expected, msg, ref mut cond, .. } => {
+            TerminatorKind::Assert { expected, ref msg, ref mut cond, .. } => {
                 if let Some(value) = self.eval_operand(&cond, source_info) {
                     trace!("assertion on {:?} should be {:?}", value, expected);
                     let expected = ScalarMaybeUndef::from(Scalar::from_bool(*expected));
@@ -836,7 +836,8 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
                             Panic(PanicMessage::Overflow(_)) |
                             Panic(PanicMessage::OverflowNeg) |
                             Panic(PanicMessage::DivisionByZero) |
-                            Panic(PanicMessage::RemainderByZero) => msg.description().to_owned(),
+                            Panic(PanicMessage::RemainderByZero) =>
+                                format!("{:?}", msg),
                             Panic(PanicMessage::BoundsCheck { ref len, ref index }) => {
                                 let len = self
                                     .eval_operand(len, source_info)