Use the new solver in the impossible_predicates

Author: compiler-errors

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -701,8 +701,11 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
 /// used during analysis.
 pub fn impossible_predicates<'tcx>(tcx: TyCtxt<'tcx>, predicates: Vec<ty::Clause<'tcx>>) -> bool {
     debug!("impossible_predicates(predicates={:?})", predicates);
-    let (infcx, param_env) =
-        tcx.infer_ctxt().build_with_typing_env(ty::TypingEnv::fully_monomorphized());
+    let (infcx, param_env) = tcx
+        .infer_ctxt()
+        .with_next_trait_solver(true)
+        .build_with_typing_env(ty::TypingEnv::fully_monomorphized());
+
     let ocx = ObligationCtxt::new(&infcx);
     let predicates = ocx.normalize(&ObligationCause::dummy(), param_env, predicates);
     for predicate in predicates {
@@ -715,13 +718,6 @@ pub fn impossible_predicates<'tcx>(tcx: TyCtxt<'tcx>, predicates: Vec<ty::Clause
         return true;
     }
 
-    // Leak check for any higher-ranked trait mismatches.
-    // We only need to do this in the old solver, since the new solver already
-    // leak-checks.
-    if !infcx.next_trait_solver() && infcx.leak_check(ty::UniverseIndex::ROOT, None).is_err() {
-        return true;
-    }
-
     false
 }