ty/instance: use ParamEnvAnd in the resolve_instance query.

src/librustc_middle/query/mod.rs

@@ -1258,8 +1258,10 @@ rustc_queries! {
             desc { "looking up enabled feature gates" }
         }
 
-        query resolve_instance(key: (ty::ParamEnv<'tcx>, DefId, SubstsRef<'tcx>)) -> Option<ty::Instance<'tcx>> {
-            desc { "resolving instance `{:?}` `{:?}` with {:?}", key.1, key.2, key.0 }
+        query resolve_instance(
+            key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>
+        ) -> Option<ty::Instance<'tcx>> {
+            desc { "resolving instance `{}`", ty::Instance::new(key.value.0, key.value.1) }
         }
     }
 }

src/librustc_middle/ty/instance.rs

@@ -290,7 +290,14 @@ impl<'tcx> Instance<'tcx> {
     ) -> Option<Instance<'tcx>> {
         // All regions in the result of this query are erased, so it's
         // fine to erase all of the input regions.
-        tcx.resolve_instance((tcx.erase_regions(&param_env), def_id, tcx.erase_regions(&substs)))
+
+        // HACK(eddyb) erase regions in `substs` first, so that `param_env.and(...)`
+        // below is more likely to ignore the bounds in scope (e.g. if the only
+        // generic parameters mentioned by `substs` were lifetime ones).
+        let substs = tcx.erase_regions(&substs);
+
+        // FIXME(eddyb) should this always use `param_env.with_reveal_all()`?
+        tcx.resolve_instance(tcx.erase_regions(&param_env.and((def_id, substs))))
     }
 
     pub fn resolve_for_fn_ptr(

src/librustc_middle/ty/query/keys.rs

@@ -296,14 +296,3 @@ impl Key for (Symbol, u32, u32) {
         DUMMY_SP
     }
 }
-
-impl<'tcx> Key for (ty::ParamEnv<'tcx>, DefId, SubstsRef<'tcx>) {
-    type CacheSelector = DefaultCacheSelector;
-
-    fn query_crate(&self) -> CrateNum {
-        self.1.krate
-    }
-    fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
-        tcx.def_span(self.1)
-    }
-}

src/librustc_ty/instance.rs

@@ -9,10 +9,12 @@ use traits::{translate_substs, Reveal};
 
 use log::debug;
 
-pub fn resolve_instance<'tcx>(
+fn resolve_instance<'tcx>(
     tcx: TyCtxt<'tcx>,
-    (param_env, def_id, substs): (ty::ParamEnv<'tcx>, DefId, SubstsRef<'tcx>),
+    key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
 ) -> Option<Instance<'tcx>> {
+    let (param_env, (def_id, substs)) = key.into_parts();
+
     debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
     let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);