debug!("paramenv={}paramenv={}paramenv={}paramenv={}")

compiler/rustc_infer/src/infer/combine.rs

@@ -228,6 +228,7 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
         ct: &'tcx ty::Const<'tcx>,
         vid_is_expected: bool,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
+        debug!("unify_const_variable: param_env={:?}", param_env);
         let (for_universe, span) = {
             let mut inner = self.inner.borrow_mut();
             let variable_table = &mut inner.const_unification_table();

compiler/rustc_middle/src/mir/interpret/queries.rs

@@ -39,6 +39,7 @@ impl<'tcx> TyCtxt<'tcx> {
         promoted: Option<mir::Promoted>,
         span: Option<Span>,
     ) -> EvalToConstValueResult<'tcx> {
+        debug!("const_eval_resolve: param_env={:?}", param_env);
         match ty::Instance::resolve_opt_const_arg(self, param_env, def, substs) {
             Ok(Some(instance)) => {
                 let cid = GlobalId { instance, promoted };

compiler/rustc_middle/src/ty/instance.rs

@@ -353,6 +353,7 @@ impl<'tcx> Instance<'tcx> {
         def: ty::WithOptConstParam<DefId>,
         substs: SubstsRef<'tcx>,
     ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
+        debug!("resolve_opt_const_arg: param_env={:?},substs={:?}", param_env, substs);
         // All regions in the result of this query are erased, so it's
         // fine to erase all of the input regions.
 

compiler/rustc_ty_utils/src/instance.rs

@@ -14,6 +14,7 @@ fn resolve_instance<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, (DefId, SubstsRef<'tcx>)>,
 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
+    debug!("resolve_instance: key = {:?}", key);
     let (param_env, (did, substs)) = key.into_parts();
     if let Some(did) = did.as_local() {
         if let Some(param_did) = tcx.opt_const_param_of(did) {
@@ -44,7 +45,7 @@ fn inner_resolve_instance<'tcx>(
 ) -> Result<Option<Instance<'tcx>>, ErrorReported> {
     let (param_env, (def, substs)) = key.into_parts();
 
-    debug!("resolve(def={:?}, substs={:?})", def.did, substs);
+    debug!("inner_resolve_instance: key={:?}", key);
     let result = if let Some(trait_def_id) = tcx.trait_of_item(def.did) {
         debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
         let item = tcx.associated_item(def.did);
@@ -93,7 +94,10 @@ fn inner_resolve_instance<'tcx>(
         };
         Ok(Some(Instance { def, substs }))
     };
-    debug!("resolve(def.did={:?}, substs={:?}) = {:?}", def.did, substs, result);
+    debug!(
+        "inner_resolve_instance: resolve(def.did={:?}, substs={:?}) = {:?}",
+        def.did, substs, result
+    );
     result
 }