Auto merge of #44741 - qmx:trans_fulfill_obligation_should_not_crash, r=nikomatsakis

use param_env on the trait_cache key

We bailed from making trans_fulfill_obligation return `Option` or `Result`, just made it less prone to crashing outside trans

r? @nikomatsakis

src/librustc/traits/trans/mod.rs

@@ -19,7 +19,7 @@ use std::cell::RefCell;
 use std::marker::PhantomData;
 use syntax::ast;
 use syntax_pos::Span;
-use traits::{FulfillmentContext, Obligation, ObligationCause, Reveal, SelectionContext, Vtable};
+use traits::{FulfillmentContext, Obligation, ObligationCause, SelectionContext, Vtable};
 use ty::{self, Ty, TyCtxt};
 use ty::subst::{Subst, Substs};
 use ty::fold::{TypeFoldable, TypeFolder};
@@ -31,24 +31,25 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
     /// (necessarily) resolve all nested obligations on the impl. Note
     /// that type check should guarantee to us that all nested
     /// obligations *could be* resolved if we wanted to.
+    /// Assumes that this is run after the entire crate has been successfully type-checked.
     pub fn trans_fulfill_obligation(self,
                                     span: Span,
+                                    param_env: ty::ParamEnv<'tcx>,
                                     trait_ref: ty::PolyTraitRef<'tcx>)
                                     -> Vtable<'tcx, ()>
     {
         // Remove any references to regions; this helps improve caching.
         let trait_ref = self.erase_regions(&trait_ref);
 
-        self.trans_trait_caches.trait_cache.memoize(trait_ref, || {
+        self.trans_trait_caches.trait_cache.memoize((param_env, trait_ref), || {
             debug!("trans::fulfill_obligation(trait_ref={:?}, def_id={:?})",
-                   trait_ref, trait_ref.def_id());
+                   (param_env, trait_ref), trait_ref.def_id());
 
             // Do the initial selection for the obligation. This yields the
             // shallow result we are looking for -- that is, what specific impl.
             self.infer_ctxt().enter(|infcx| {
                 let mut selcx = SelectionContext::new(&infcx);
 
-                let param_env = ty::ParamEnv::empty(Reveal::All);
                 let obligation_cause = ObligationCause::misc(span,
                                                              ast::DUMMY_NODE_ID);
                 let obligation = Obligation::new(obligation_cause,
@@ -167,7 +168,7 @@ pub struct TraitSelectionCache<'tcx> {
 }
 
 impl<'tcx> DepTrackingMapConfig for TraitSelectionCache<'tcx> {
-    type Key = ty::PolyTraitRef<'tcx>;
+    type Key = (ty::ParamEnv<'tcx>, ty::PolyTraitRef<'tcx>);
     type Value = Vtable<'tcx, ()>;
     fn to_dep_kind() -> DepKind {
         DepKind::TraitSelect

src/librustc_trans/monomorphize.rs

@@ -112,7 +112,8 @@ fn resolve_associated_item<'a, 'tcx>(
            def_id, trait_id, rcvr_substs);
 
     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
-    let vtbl = tcx.trans_fulfill_obligation(DUMMY_SP, ty::Binder(trait_ref));
+    let vtbl = tcx.trans_fulfill_obligation(
+        DUMMY_SP, ty::ParamEnv::empty(traits::Reveal::All), ty::Binder(trait_ref));
 
     // Now that we know which impl is being used, we can dispatch to
     // the actual function:
@@ -226,7 +227,8 @@ pub fn custom_coerce_unsize_info<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         substs: tcx.mk_substs_trait(source_ty, &[target_ty])
     });
 
-    match tcx.trans_fulfill_obligation(DUMMY_SP, trait_ref) {
+    match tcx.trans_fulfill_obligation(
+        DUMMY_SP, ty::ParamEnv::empty(traits::Reveal::All), trait_ref) {
         traits::VtableImpl(traits::VtableImplData { impl_def_id, .. }) => {
             tcx.coerce_unsized_info(impl_def_id).custom_kind.unwrap()
         }

src/tools/toolstate.toml

@@ -23,7 +23,7 @@
 # Each tool has a list of people to ping
 
 # ping @oli-obk @RalfJung @eddyb
-miri = "Testing"
+miri = "Broken"
 
 # ping @Manishearth @llogiq @mcarton @oli-obk
 clippy = "Broken"