use reveal_all during drop elaboration

This used to happen by default as part of the normalization routine
that was being used.

Author: nikomatsakis

src/librustc_mir/shim.rs

@@ -210,7 +210,7 @@ fn build_drop_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     if let Some(..) = ty {
         let patch = {
-            let param_env = tcx.param_env(def_id);
+            let param_env = tcx.param_env(def_id).with_reveal_all();
             let mut elaborator = DropShimElaborator {
                 mir: &mir,
                 patch: MirPatch::new(&mir),

src/librustc_mir/transform/elaborate_drops.rs

@@ -50,7 +50,7 @@ impl MirPass for ElaborateDrops {
             (hir::BodyOwnerKind::Fn, None) => {},
             _ => return
         }
-        let param_env = tcx.param_env(src.def_id);
+        let param_env = tcx.param_env(src.def_id).with_reveal_all();
         let move_data = MoveData::gather_moves(mir, tcx).unwrap();
         let elaborate_patch = {
             let mir = &*mir;

src/librustc_mir/util/elaborate_drops.rs

@@ -13,6 +13,7 @@ use rustc::hir;
 use rustc::mir::*;
 use rustc::middle::const_val::ConstVal;
 use rustc::middle::lang_items;
+use rustc::traits::Reveal;
 use rustc::ty::{self, Ty, TyCtxt};
 use rustc::ty::subst::{Kind, Substs};
 use rustc::ty::util::IntTypeExt;
@@ -206,6 +207,7 @@ impl<'l, 'b, 'tcx, D> DropCtxt<'l, 'b, 'tcx, D>
             let field = Field::new(i);
             let subpath = self.elaborator.field_subpath(variant_path, field);
 
+            assert_eq!(self.elaborator.param_env().reveal, Reveal::All);
             let field_ty = self.tcx().normalize_erasing_regions(
                 self.elaborator.param_env(),
                 f.ty(self.tcx(), substs),