Fix an ICE that can occur while errors are already being emitted

Author: oli-obk

src/librustc/ty/sty.rs

@@ -1975,8 +1975,12 @@ impl<'tcx> Const<'tcx> {
         ty: ParamEnvAnd<'tcx, Ty<'tcx>>,
     ) -> &'tcx Self {
         let ty = tcx.lift_to_global(&ty).unwrap();
-        let layout = tcx.layout_of(ty).unwrap_or_else(|e| {
-            panic!("could not compute layout for {:?}: {:?}", ty, e)
+        let layout = tcx.layout_of(ty).unwrap_or_else(|_| {
+            // FIXME: add delay_span_bug call, we can only get here if there are errors
+            // we produce a weird dummy layout with somewhat sane values
+            let mut layout = tcx.layout_of(ParamEnv::reveal_all().and(tcx.types.u128)).unwrap();
+            layout.ty = ty.value;
+            layout
         });
         let mut bytes = [0_u8; 16];
         let endian = tcx.data_layout.endian;