make ConstEvaluatable more strict

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -6,6 +6,7 @@ use self::EvaluationResult::*;
 use self::SelectionCandidate::*;
 
 use super::coherence::{self, Conflict};
+use super::const_evaluatable;
 use super::project;
 use super::project::normalize_with_depth_to;
 use super::util;
@@ -542,17 +543,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
 
             ty::PredicateAtom::ConstEvaluatable(def_id, substs) => {
-                match self.tcx().const_eval_resolve(
-                    obligation.param_env,
+                const_evaluatable::is_const_evaluatable(
+                    self.infcx,
                     def_id,
                     substs,
-                    None,
-                    None,
-                ) {
-                    Ok(_) => Ok(EvaluatedToOk),
-                    Err(ErrorHandled::TooGeneric) => Ok(EvaluatedToAmbig),
-                    Err(_) => Ok(EvaluatedToErr),
-                }
+                    obligation.param_env,
+                    obligation.cause.span,
+                )
+                .map(|()| EvaluatedToOk)
+                .or_else(|e| match e {
+                    ErrorHandled::TooGeneric => Ok(EvaluatedToAmbig),
+                    _ => Ok(EvaluatedToErr),
+                })
             }
 
             ty::PredicateAtom::ConstEquate(c1, c2) => {