Minor [const] tweaks

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -390,45 +390,13 @@ fn check_predicates<'tcx>(
 
     let mut res = Ok(());
     for (clause, span) in impl1_predicates {
-        if !impl2_predicates.iter().any(|pred2| trait_predicates_eq(clause.as_predicate(), *pred2))
-        {
+        if !impl2_predicates.iter().any(|&pred2| clause.as_predicate() == pred2) {
             res = res.and(check_specialization_on(tcx, clause, span))
         }
     }
     res
 }
 
-/// Checks if some predicate on the specializing impl (`predicate1`) is the same
-/// as some predicate on the base impl (`predicate2`).
-///
-/// This basically just checks syntactic equivalence, but is a little more
-/// forgiving since we want to equate `T: Tr` with `T: [const] Tr` so this can work:
-///
-/// ```ignore (illustrative)
-/// #[rustc_specialization_trait]
-/// trait Specialize { }
-///
-/// impl<T: Bound> Tr for T { }
-/// impl<T: [const] Bound + Specialize> const Tr for T { }
-/// ```
-///
-/// However, we *don't* want to allow the reverse, i.e., when the bound on the
-/// specializing impl is not as const as the bound on the base impl:
-///
-/// ```ignore (illustrative)
-/// impl<T: [const] Bound> const Tr for T { }
-/// impl<T: Bound + Specialize> const Tr for T { } // should be T: [const] Bound
-/// ```
-///
-/// So we make that check in this function and try to raise a helpful error message.
-fn trait_predicates_eq<'tcx>(
-    predicate1: ty::Predicate<'tcx>,
-    predicate2: ty::Predicate<'tcx>,
-) -> bool {
-    // FIXME(const_trait_impl)
-    predicate1 == predicate2
-}
-
 #[instrument(level = "debug", skip(tcx))]
 fn check_specialization_on<'tcx>(
     tcx: TyCtxt<'tcx>,

compiler/rustc_hir_typeck/src/callee.rs

@@ -910,7 +910,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // const stability checking here too, I guess.
         if self.tcx.is_conditionally_const(callee_did) {
             let q = self.tcx.const_conditions(callee_did);
-            // FIXME(const_trait_impl): Use this span with a better cause code.
             for (idx, (cond, pred_span)) in
                 q.instantiate(self.tcx, callee_args).into_iter().enumerate()
             {

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -37,7 +37,6 @@ use super::on_unimplemented::{AppendConstMessage, OnUnimplementedNote};
 use super::suggestions::get_explanation_based_on_obligation;
 use super::{
     ArgKind, CandidateSimilarity, FindExprBySpan, GetSafeTransmuteErrorAndReason, ImplCandidate,
-    UnsatisfiedConst,
 };
 use crate::error_reporting::TypeErrCtxt;
 use crate::error_reporting::infer::TyCategory;
@@ -374,13 +373,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             }
                         }
 
-                        let UnsatisfiedConst(unsatisfied_const) = self
-                            .maybe_add_note_for_unsatisfied_const(
-                                leaf_trait_predicate,
-                                &mut err,
-                                span,
-                            );
-
                         if let Some((msg, span)) = type_def {
                             err.span_label(span, msg);
                         }
@@ -506,7 +498,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             span,
                             is_fn_trait,
                             suggested,
-                            unsatisfied_const,
                         );
 
                         // Changing mutability doesn't make a difference to whether we have
@@ -2716,7 +2707,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         span: Span,
         is_fn_trait: bool,
         suggested: bool,
-        unsatisfied_const: bool,
     ) {
         let body_def_id = obligation.cause.body_id;
         let span = if let ObligationCauseCode::BinOp { rhs_span: Some(rhs_span), .. } =
@@ -2763,10 +2753,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 self.tcx.def_span(trait_def_id),
                 crate::fluent_generated::trait_selection_trait_has_no_impls,
             );
-        } else if !suggested
-            && !unsatisfied_const
-            && trait_predicate.polarity() == ty::PredicatePolarity::Positive
-        {
+        } else if !suggested && trait_predicate.polarity() == ty::PredicatePolarity::Positive {
             // 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(
@@ -2878,17 +2865,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         }
     }
 
-    fn maybe_add_note_for_unsatisfied_const(
-        &self,
-        _trait_predicate: ty::PolyTraitPredicate<'tcx>,
-        _err: &mut Diag<'_>,
-        _span: Span,
-    ) -> UnsatisfiedConst {
-        let unsatisfied_const = UnsatisfiedConst(false);
-        // FIXME(const_trait_impl)
-        unsatisfied_const
-    }
-
     fn report_closure_error(
         &self,
         obligation: &PredicateObligation<'tcx>,

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

@@ -51,8 +51,6 @@ enum GetSafeTransmuteErrorAndReason {
     Error { err_msg: String, safe_transmute_explanation: Option<String> },
 }
 
-struct UnsatisfiedConst(pub bool);
-
 /// Crude way of getting back an `Expr` from a `Span`.
 pub struct FindExprBySpan<'hir> {
     pub span: Span,