Rollup merge of #103328 - compiler-errors:trivial-false-const-sugg, r=jackh726

Do not suggest trivially false const predicates

Pass through constness to `predicate_can_apply` and don't suggest other impls if it's satisfied but not const.

Fixes #103267

1 files changed, 7 insertions, 5 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index fc0040de6b3..1217d264a9c 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -764,6 +764,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             self.suggest_borrowing_for_object_cast(&mut err, &root_obligation, *concrete_ty, *obj_ty);
                         }
 
+                        let mut unsatisfied_const = false;
                         if trait_predicate.is_const_if_const() && obligation.param_env.is_const() {
                             let non_const_predicate = trait_ref.without_const();
                             let non_const_obligation = Obligation {
@@ -773,6 +774,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 recursion_depth: obligation.recursion_depth,
                             };
                             if self.predicate_may_hold(&non_const_obligation) {
+                                unsatisfied_const = true;
                                 err.span_note(
                                     span,
                                     &format!(
@@ -924,7 +926,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 }
                             }
                         } else if !trait_ref.has_non_region_infer()
-                            && self.predicate_can_apply(obligation.param_env, trait_ref)
+                            && self.predicate_can_apply(obligation.param_env, trait_predicate)
                         {
                             // If a where-clause may be useful, remind the
                             // user that they can add it.
@@ -939,7 +941,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 None,
                                 obligation.cause.body_id,
                             );
-                        } else if !suggested {
+                        } else if !suggested && !unsatisfied_const {
                             // Can't show anything else useful, try to find similar impls.
                             let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
                             if !self.report_similar_impl_candidates(
@@ -1436,7 +1438,7 @@ trait InferCtxtPrivExt<'tcx> {
     fn predicate_can_apply(
         &self,
         param_env: ty::ParamEnv<'tcx>,
-        pred: ty::PolyTraitRef<'tcx>,
+        pred: ty::PolyTraitPredicate<'tcx>,
     ) -> bool;
 
     fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
@@ -2511,7 +2513,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     fn predicate_can_apply(
         &self,
         param_env: ty::ParamEnv<'tcx>,
-        pred: ty::PolyTraitRef<'tcx>,
+        pred: ty::PolyTraitPredicate<'tcx>,
     ) -> bool {
         struct ParamToVarFolder<'a, 'tcx> {
             infcx: &'a InferCtxt<'tcx>,
@@ -2555,7 +2557,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             let obligation = Obligation::new(
                 ObligationCause::dummy(),
                 param_env,
-                cleaned_pred.without_const().to_predicate(selcx.tcx()),
+                cleaned_pred.to_predicate(selcx.tcx()),
             );
 
             self.predicate_may_hold(&obligation)