unify Instance::resolve

Author: lcnr

src/librustc_middle/mir/interpret/queries.rs

@@ -39,7 +39,7 @@ impl<'tcx> TyCtxt<'tcx> {
         promoted: Option<mir::Promoted>,
         span: Option<Span>,
     ) -> ConstEvalResult<'tcx> {
-        match ty::Instance::resolve_const_arg(self, param_env, def, substs) {
+        match ty::Instance::resolve_opt_const_arg(self, param_env, def, substs) {
             Ok(Some(instance)) => {
                 let cid = GlobalId { instance, promoted };
                 self.const_eval_global_id(param_env, cid, span)

src/librustc_middle/ty/instance.rs

@@ -339,27 +339,30 @@ impl<'tcx> Instance<'tcx> {
         def_id: DefId,
         substs: SubstsRef<'tcx>,
     ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
-        // All regions in the result of this query are erased, so it's
-        // fine to erase all of the input regions.
-
-        // 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))))
+        Instance::resolve_opt_const_arg(
+            tcx,
+            param_env,
+            ty::WithOptConstParam::unknown(def_id),
+            substs,
+        )
     }
 
     // This should be kept up to date with `resolve`.
-    pub fn resolve_const_arg(
+    pub fn resolve_opt_const_arg(
         tcx: TyCtxt<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         def: ty::WithOptConstParam<DefId>,
         substs: SubstsRef<'tcx>,
     ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
+        // All regions in the result of this query are erased, so it's
+        // fine to erase all of the input regions.
+
+        // 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()`?
         if let Some((did, param_did)) = def.as_const_arg() {
             tcx.resolve_instance_of_const_arg(
                 tcx.erase_regions(&param_env.and((did, param_did, substs))),