Rip out old effects var handling code from traits

14 files changed, 34 insertions, 491 deletions

diff --git a/compiler/rustc_const_eval/src/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/check_consts/qualifs.rs
index 7358a6c6d22..547030a1854 100644
--- a/compiler/rustc_const_eval/src/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/check_consts/qualifs.rs
@@ -6,13 +6,10 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_hir::LangItem;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::*;
-use rustc_middle::traits::BuiltinImplSource;
 use rustc_middle::ty::{self, AdtDef, GenericArgsRef, Ty};
 use rustc_middle::{bug, mir};
-use rustc_trait_selection::traits::{
-    ImplSource, Obligation, ObligationCause, ObligationCtxt, SelectionContext,
-};
-use tracing::{instrument, trace};
+use rustc_trait_selection::traits::{Obligation, ObligationCause, ObligationCtxt};
+use tracing::instrument;
 
 use super::ConstCx;
 
@@ -195,50 +192,8 @@ impl Qualif for NeedsNonConstDrop {
             return false;
         }
 
-        // FIXME(effects): If `destruct` is not a `const_trait`,
-        // or effects are disabled in this crate, then give up.
-        let destruct_def_id = cx.tcx.require_lang_item(LangItem::Destruct, Some(cx.body.span));
-        if !cx.tcx.has_host_param(destruct_def_id) || !cx.tcx.features().effects {
-            return NeedsDrop::in_any_value_of_ty(cx, ty);
-        }
-
-        let obligation = Obligation::new(
-            cx.tcx,
-            ObligationCause::dummy_with_span(cx.body.span),
-            cx.param_env,
-            ty::TraitRef::new(cx.tcx, destruct_def_id, [
-                ty::GenericArg::from(ty),
-                ty::GenericArg::from(cx.tcx.expected_host_effect_param_for_body(cx.def_id())),
-            ]),
-        );
-
-        let infcx = cx.tcx.infer_ctxt().build();
-        let mut selcx = SelectionContext::new(&infcx);
-        let Some(impl_src) = selcx.select(&obligation).ok().flatten() else {
-            // If we couldn't select a const destruct candidate, then it's bad
-            return true;
-        };
-
-        trace!(?impl_src);
-
-        if !matches!(
-            impl_src,
-            ImplSource::Builtin(BuiltinImplSource::Misc, _) | ImplSource::Param(_)
-        ) {
-            // If our const destruct candidate is not ConstDestruct or implied by the param env,
-            // then it's bad
-            return true;
-        }
-
-        if impl_src.borrow_nested_obligations().is_empty() {
-            return false;
-        }
-
-        // If we had any errors, then it's bad
-        let ocx = ObligationCtxt::new(&infcx);
-        ocx.register_obligations(impl_src.nested_obligations());
-        let errors = ocx.select_all_or_error();
-        !errors.is_empty()
+        // FIXME(effects): Reimplement const drop checking.
+        NeedsDrop::in_any_value_of_ty(cx, ty)
     }
 
     fn in_adt_inherently<'tcx>(
diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index 13ba615d4c9..fa6a86c6911 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -537,40 +537,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 //
                 // This check is here because there is currently no way to express a trait bound for `FnDef` types only.
                 if let ty::FnDef(def_id, _args) = *arg_ty.kind() {
-                    let fn_once_def_id =
-                        self.tcx.require_lang_item(hir::LangItem::FnOnce, Some(span));
-                    let fn_once_output_def_id =
-                        self.tcx.require_lang_item(hir::LangItem::FnOnceOutput, Some(span));
-                    if self.tcx.has_host_param(fn_once_def_id) {
-                        let const_param: ty::GenericArg<'tcx> =
-                            ([self.tcx.consts.false_, self.tcx.consts.true_])[idx].into();
-                        self.register_predicate(traits::Obligation::new(
-                            self.tcx,
-                            self.misc(span),
-                            self.param_env,
-                            ty::TraitRef::new(self.tcx, fn_once_def_id, [
-                                arg_ty.into(),
-                                fn_sig.inputs()[0].into(),
-                                const_param,
-                            ]),
-                        ));
-
-                        self.register_predicate(traits::Obligation::new(
-                            self.tcx,
-                            self.misc(span),
-                            self.param_env,
-                            ty::ProjectionPredicate {
-                                projection_term: ty::AliasTerm::new(
-                                    self.tcx,
-                                    fn_once_output_def_id,
-                                    [arg_ty.into(), fn_sig.inputs()[0].into(), const_param],
-                                ),
-                                term: fn_sig.output().into(),
-                            },
-                        ));
-
-                        self.select_obligations_where_possible(|_| {});
-                    } else if idx == 0 && !self.tcx.is_const_fn_raw(def_id) {
+                    if idx == 0 && !self.tcx.is_const_fn_raw(def_id) {
                         self.dcx().emit_err(errors::ConstSelectMustBeConst { span });
                     }
                 } else {
diff --git a/compiler/rustc_middle/src/traits/select.rs b/compiler/rustc_middle/src/traits/select.rs
index 66035464fa5..05556ae38a8 100644
--- a/compiler/rustc_middle/src/traits/select.rs
+++ b/compiler/rustc_middle/src/traits/select.rs
@@ -161,9 +161,7 @@ pub enum SelectionCandidate<'tcx> {
 
     /// Implementation of a `Fn`-family trait by one of the anonymous
     /// types generated for a fn pointer type (e.g., `fn(int) -> int`)
-    FnPointerCandidate {
-        fn_host_effect: ty::Const<'tcx>,
-    },
+    FnPointerCandidate,
 
     TraitAliasCandidate,
 
@@ -180,9 +178,6 @@ pub enum SelectionCandidate<'tcx> {
     BuiltinObjectCandidate,
 
     BuiltinUnsizeCandidate,
-
-    /// Implementation of `const Destruct`, optionally from a custom `impl const Drop`.
-    ConstDestructCandidate(Option<DefId>),
 }
 
 /// The result of trait evaluation. The order is important
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index 0a917120b3b..9a3049f3be6 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -907,24 +907,6 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
-    /// Constructs generic args for an item, optionally appending a const effect param type
-    pub fn with_opt_host_effect_param(
-        self,
-        caller_def_id: LocalDefId,
-        callee_def_id: DefId,
-        args: impl IntoIterator<Item: Into<ty::GenericArg<'tcx>>>,
-    ) -> ty::GenericArgsRef<'tcx> {
-        let generics = self.generics_of(callee_def_id);
-        assert_eq!(generics.parent, None);
-
-        let opt_const_param = generics
-            .host_effect_index
-            .is_some()
-            .then(|| ty::GenericArg::from(self.expected_host_effect_param_for_body(caller_def_id)));
-
-        self.mk_args_from_iter(args.into_iter().map(|arg| arg.into()).chain(opt_const_param))
-    }
-
     /// Expand any [weak alias types][weak] contained within the given `value`.
     ///
     /// This should be used over other normalization routines in situations where
diff --git a/compiler/rustc_mir_build/src/build/matches/test.rs b/compiler/rustc_mir_build/src/build/matches/test.rs
index 020c202f965..7170aebee7d 100644
--- a/compiler/rustc_mir_build/src/build/matches/test.rs
+++ b/compiler/rustc_mir_build/src/build/matches/test.rs
@@ -454,12 +454,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         };
 
         let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, Some(source_info.span));
-        let method = trait_method(
-            self.tcx,
-            eq_def_id,
-            sym::eq,
-            self.tcx.with_opt_host_effect_param(self.def_id, eq_def_id, [compare_ty, compare_ty]),
-        );
+        let method = trait_method(self.tcx, eq_def_id, sym::eq, [compare_ty, compare_ty]);
 
         let bool_ty = self.tcx.types.bool;
         let eq_result = self.temp(bool_ty, source_info.span);
diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
index 2c3611afca9..0dfa9168f7c 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
@@ -43,7 +43,6 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 }
 
 struct ConstToPat<'tcx> {
-    id: hir::HirId,
     span: Span,
     param_env: ty::ParamEnv<'tcx>,
 
@@ -62,7 +61,6 @@ impl<'tcx> ConstToPat<'tcx> {
     ) -> Self {
         trace!(?pat_ctxt.typeck_results.hir_owner);
         ConstToPat {
-            id,
             span,
             infcx,
             param_env: pat_ctxt.param_env,
@@ -149,15 +147,7 @@ impl<'tcx> ConstToPat<'tcx> {
             tcx,
             ObligationCause::dummy(),
             self.param_env,
-            ty::TraitRef::new_from_args(
-                tcx,
-                partial_eq_trait_id,
-                tcx.with_opt_host_effect_param(
-                    tcx.hir().enclosing_body_owner(self.id),
-                    partial_eq_trait_id,
-                    [ty, ty],
-                ),
-            ),
+            ty::TraitRef::new(tcx, partial_eq_trait_id, [ty, ty]),
         );
 
         // This *could* accept a type that isn't actually `PartialEq`, because region bounds get
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
index 733baaa99e5..677905a3085 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -3701,12 +3701,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         }
                         _ => None,
                     };
-                    // Also add host param, if present
-                    let host = self.tcx.generics_of(trait_pred.def_id()).host_effect_index.map(|idx| trait_pred.skip_binder().trait_ref.args[idx]);
                     let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
                         trait_ref: ty::TraitRef::new(self.tcx,
                             trait_pred.def_id(),
-                            [field_ty].into_iter().chain(trait_args).chain(host),
+                            [field_ty].into_iter().chain(trait_args),
                         ),
                         ..*tr
                     });
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 7f7c9bced18..cc634b65a0b 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -1642,24 +1642,9 @@ fn confirm_fn_pointer_candidate<'cx, 'tcx>(
         sig,
     );
 
-    let host_effect_param = match *fn_type.kind() {
-        ty::FnDef(def_id, args) => tcx
-            .generics_of(def_id)
-            .host_effect_index
-            .map_or(tcx.consts.true_, |idx| args.const_at(idx)),
-        ty::FnPtr(..) => tcx.consts.true_,
-        _ => unreachable!("only expected FnPtr or FnDef in `confirm_fn_pointer_candidate`"),
-    };
-
-    confirm_callable_candidate(
-        selcx,
-        obligation,
-        sig,
-        util::TupleArgumentsFlag::Yes,
-        host_effect_param,
-    )
-    .with_addl_obligations(nested)
-    .with_addl_obligations(obligations)
+    confirm_callable_candidate(selcx, obligation, sig, util::TupleArgumentsFlag::Yes)
+        .with_addl_obligations(nested)
+        .with_addl_obligations(obligations)
 }
 
 fn confirm_closure_candidate<'cx, 'tcx>(
@@ -1739,16 +1724,9 @@ fn confirm_closure_candidate<'cx, 'tcx>(
 
     debug!(?obligation, ?closure_sig, ?obligations, "confirm_closure_candidate");
 
-    confirm_callable_candidate(
-        selcx,
-        obligation,
-        closure_sig,
-        util::TupleArgumentsFlag::No,
-        // FIXME(effects): This doesn't handle const closures correctly!
-        selcx.tcx().consts.true_,
-    )
-    .with_addl_obligations(nested)
-    .with_addl_obligations(obligations)
+    confirm_callable_candidate(selcx, obligation, closure_sig, util::TupleArgumentsFlag::No)
+        .with_addl_obligations(nested)
+        .with_addl_obligations(obligations)
 }
 
 fn confirm_callable_candidate<'cx, 'tcx>(
@@ -1756,7 +1734,6 @@ fn confirm_callable_candidate<'cx, 'tcx>(
     obligation: &ProjectionTermObligation<'tcx>,
     fn_sig: ty::PolyFnSig<'tcx>,
     flag: util::TupleArgumentsFlag,
-    fn_host_effect: ty::Const<'tcx>,
 ) -> Progress<'tcx> {
     let tcx = selcx.tcx();
 
@@ -1771,7 +1748,6 @@ fn confirm_callable_candidate<'cx, 'tcx>(
         obligation.predicate.self_ty(),
         fn_sig,
         flag,
-        fn_host_effect,
     )
     .map_bound(|(trait_ref, ret_type)| ty::ProjectionPredicate {
         projection_term: ty::AliasTerm::new_from_args(tcx, fn_once_output_def_id, trait_ref.args),
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index aa313a526c1..ac38c9e24a2 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -543,23 +543,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // Provide an impl, but only for suitable `fn` pointers.
             ty::FnPtr(sig_tys, hdr) => {
                 if sig_tys.with(hdr).is_fn_trait_compatible() {
-                    candidates
-                        .vec
-                        .push(FnPointerCandidate { fn_host_effect: self.tcx().consts.true_ });
+                    candidates.vec.push(FnPointerCandidate);
                 }
             }
             // Provide an impl for suitable functions, rejecting `#[target_feature]` functions (RFC 2396).
-            ty::FnDef(def_id, args) => {
+            ty::FnDef(def_id, _args) => {
                 let tcx = self.tcx();
                 if tcx.fn_sig(def_id).skip_binder().is_fn_trait_compatible()
                     && tcx.codegen_fn_attrs(def_id).target_features.is_empty()
                 {
-                    candidates.vec.push(FnPointerCandidate {
-                        fn_host_effect: tcx
-                            .generics_of(def_id)
-                            .host_effect_index
-                            .map_or(tcx.consts.true_, |idx| args.const_at(idx)),
-                    });
+                    candidates.vec.push(FnPointerCandidate);
                 }
             }
             _ => {}
@@ -1170,103 +1163,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
     fn assemble_const_destruct_candidates(
         &mut self,
-        obligation: &PolyTraitObligation<'tcx>,
+        _obligation: &PolyTraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
-        // If the predicate is `~const Destruct` in a non-const environment, we don't actually need
-        // to check anything. We'll short-circuit checking any obligations in confirmation, too.
-        let Some(host_effect_index) =
-            self.tcx().generics_of(obligation.predicate.def_id()).host_effect_index
-        else {
-            candidates.vec.push(BuiltinCandidate { has_nested: false });
-            return;
-        };
-        // If the obligation has `host = true`, then the obligation is non-const and it's always
-        // trivially implemented.
-        if obligation.predicate.skip_binder().trait_ref.args.const_at(host_effect_index)
-            == self.tcx().consts.true_
-        {
-            candidates.vec.push(BuiltinCandidate { has_nested: false });
-            return;
-        }
-
-        let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder());
-        match self_ty.kind() {
-            ty::Alias(..)
-            | ty::Dynamic(..)
-            | ty::Error(_)
-            | ty::Bound(..)
-            | ty::Param(_)
-            | ty::Placeholder(_) => {
-                // We don't know if these are `~const Destruct`, at least
-                // not structurally... so don't push a candidate.
-            }
-
-            ty::Bool
-            | ty::Char
-            | ty::Int(_)
-            | ty::Uint(_)
-            | ty::Float(_)
-            | ty::Infer(ty::IntVar(_))
-            | ty::Infer(ty::FloatVar(_))
-            | ty::Str
-            | ty::RawPtr(_, _)
-            | ty::Ref(..)
-            | ty::FnDef(..)
-            | ty::FnPtr(..)
-            | ty::Never
-            | ty::Foreign(_)
-            | ty::Array(..)
-            | ty::Pat(..)
-            | ty::Slice(_)
-            | ty::Closure(..)
-            | ty::CoroutineClosure(..)
-            | ty::Coroutine(..)
-            | ty::Tuple(_)
-            | ty::CoroutineWitness(..) => {
-                // These are built-in, and cannot have a custom `impl const Destruct`.
-                candidates.vec.push(ConstDestructCandidate(None));
-            }
-
-            ty::Adt(..) => {
-                let mut relevant_impl = None;
-                self.tcx().for_each_relevant_impl(
-                    self.tcx().require_lang_item(LangItem::Drop, None),
-                    obligation.predicate.skip_binder().trait_ref.self_ty(),
-                    |impl_def_id| {
-                        if let Some(old_impl_def_id) = relevant_impl {
-                            self.tcx()
-                                .dcx()
-                                .struct_span_err(
-                                    self.tcx().def_span(impl_def_id),
-                                    "multiple drop impls found",
-                                )
-                                .with_span_note(
-                                    self.tcx().def_span(old_impl_def_id),
-                                    "other impl here",
-                                )
-                                .delay_as_bug();
-                        }
-
-                        relevant_impl = Some(impl_def_id);
-                    },
-                );
-
-                if let Some(impl_def_id) = relevant_impl {
-                    // Check that `impl Drop` is actually const, if there is a custom impl
-                    if self.tcx().constness(impl_def_id) == hir::Constness::Const {
-                        candidates.vec.push(ConstDestructCandidate(Some(impl_def_id)));
-                    }
-                } else {
-                    // Otherwise check the ADT like a built-in type (structurally)
-                    candidates.vec.push(ConstDestructCandidate(None));
-                }
-            }
-
-            ty::Infer(_) => {
-                candidates.ambiguous = true;
-            }
-        }
+        // FIXME(effects): Destruct is not const yet, and it is implemented
+        // by all types today in non-const setting.
+        candidates.vec.push(BuiltinCandidate { has_nested: false });
     }
 
     fn assemble_candidate_for_tuple(
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 0ba3b4e6e55..1764777ee69 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -28,9 +28,9 @@ use super::{BuiltinImplConditions, PredicateObligations, SelectionContext};
 use crate::traits::normalize::{normalize_with_depth, normalize_with_depth_to};
 use crate::traits::util::{self, closure_trait_ref_and_return_type};
 use crate::traits::{
-    ImplDerivedCause, ImplSource, ImplSourceUserDefinedData, Normalized, Obligation,
-    ObligationCause, PolyTraitObligation, PredicateObligation, Selection, SelectionError,
-    SignatureMismatch, TraitDynIncompatible, TraitObligation, Unimplemented,
+    ImplSource, ImplSourceUserDefinedData, Normalized, Obligation, ObligationCause,
+    PolyTraitObligation, PredicateObligation, Selection, SelectionError, SignatureMismatch,
+    TraitDynIncompatible, TraitObligation, Unimplemented,
 };
 
 impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
@@ -109,8 +109,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplSource::Builtin(BuiltinImplSource::Misc, vtable_iterator)
             }
 
-            FnPointerCandidate { fn_host_effect } => {
-                let data = self.confirm_fn_pointer_candidate(obligation, fn_host_effect)?;
+            FnPointerCandidate => {
+                let data = self.confirm_fn_pointer_candidate(obligation)?;
                 ImplSource::Builtin(BuiltinImplSource::Misc, data)
             }
 
@@ -131,11 +131,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             TraitUpcastingUnsizeCandidate(idx) => {
                 self.confirm_trait_upcasting_unsize_candidate(obligation, idx)?
             }
-
-            ConstDestructCandidate(def_id) => {
-                let data = self.confirm_const_destruct_candidate(obligation, def_id)?;
-                ImplSource::Builtin(BuiltinImplSource::Misc, data)
-            }
         };
 
         // The obligations returned by confirmation are recursively evaluated
@@ -708,7 +703,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     fn confirm_fn_pointer_candidate(
         &mut self,
         obligation: &PolyTraitObligation<'tcx>,
-        fn_host_effect: ty::Const<'tcx>,
     ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
         debug!(?obligation, "confirm_fn_pointer_candidate");
         let placeholder_predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
@@ -722,7 +716,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             self_ty,
             sig,
             util::TupleArgumentsFlag::Yes,
-            fn_host_effect,
         )
         .map_bound(|(trait_ref, _)| trait_ref);
 
@@ -904,11 +897,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let self_ty: Ty<'_> = self.infcx.shallow_resolve(placeholder_predicate.self_ty());
 
         let trait_ref = match *self_ty.kind() {
-            ty::Closure(..) => self.closure_trait_ref_unnormalized(
-                self_ty,
-                obligation.predicate.def_id(),
-                self.tcx().consts.true_,
-            ),
+            ty::Closure(..) => {
+                self.closure_trait_ref_unnormalized(self_ty, obligation.predicate.def_id())
+            }
             ty::CoroutineClosure(_, args) => {
                 args.as_coroutine_closure().coroutine_closure_sig().map_bound(|sig| {
                     ty::TraitRef::new(self.tcx(), obligation.predicate.def_id(), [
@@ -1341,170 +1332,4 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             _ => bug!("source: {source}, target: {target}"),
         })
     }
-
-    fn confirm_const_destruct_candidate(
-        &mut self,
-        obligation: &PolyTraitObligation<'tcx>,
-        impl_def_id: Option<DefId>,
-    ) -> Result<PredicateObligations<'tcx>, SelectionError<'tcx>> {
-        let Some(host_effect_index) =
-            self.tcx().generics_of(obligation.predicate.def_id()).host_effect_index
-        else {
-            bug!()
-        };
-        let host_effect_param: ty::GenericArg<'tcx> =
-            obligation.predicate.skip_binder().trait_ref.args.const_at(host_effect_index).into();
-
-        let drop_trait = self.tcx().require_lang_item(LangItem::Drop, None);
-
-        let tcx = self.tcx();
-        let self_ty = obligation.self_ty().map_bound(|ty| self.infcx.shallow_resolve(ty));
-
-        let mut nested = PredicateObligations::new();
-        let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
-
-        // If we have a custom `impl const Drop`, then
-        // first check it like a regular impl candidate.
-        // This is copied from confirm_impl_candidate but remaps the predicate to `~const Drop` beforehand.
-        if let Some(impl_def_id) = impl_def_id {
-            let mut new_obligation = obligation.clone();
-            new_obligation.predicate = new_obligation.predicate.map_bound(|mut trait_pred| {
-                trait_pred.trait_ref.def_id = drop_trait;
-                trait_pred
-            });
-            let args = self.rematch_impl(impl_def_id, &new_obligation);
-            debug!(?args, "impl args");
-
-            let cause = obligation.derived_cause(|derived| {
-                ObligationCauseCode::ImplDerived(Box::new(ImplDerivedCause {
-                    derived,
-                    impl_or_alias_def_id: impl_def_id,
-                    impl_def_predicate_index: None,
-                    span: obligation.cause.span,
-                }))
-            });
-            let obligations = ensure_sufficient_stack(|| {
-                self.vtable_impl(
-                    impl_def_id,
-                    args,
-                    &cause,
-                    new_obligation.recursion_depth + 1,
-                    new_obligation.param_env,
-                    obligation.predicate,
-                )
-            });
-            nested.extend(obligations.nested);
-        }
-
-        // We want to confirm the ADT's fields if we have an ADT
-        let mut stack = match *self_ty.skip_binder().kind() {
-            ty::Adt(def, args) => def.all_fields().map(|f| f.ty(tcx, args)).collect(),
-            _ => vec![self_ty.skip_binder()],
-        };
-
-        while let Some(nested_ty) = stack.pop() {
-            match *nested_ty.kind() {
-                // We know these types are trivially drop
-                ty::Bool
-                | ty::Char
-                | ty::Int(_)
-                | ty::Uint(_)
-                | ty::Float(_)
-                | ty::Infer(ty::IntVar(_))
-                | ty::Infer(ty::FloatVar(_))
-                | ty::Str
-                | ty::RawPtr(_, _)
-                | ty::Ref(..)
-                | ty::FnDef(..)
-                | ty::FnPtr(..)
-                | ty::Never
-                | ty::Foreign(_) => {}
-
-                // `ManuallyDrop` is trivially drop
-                ty::Adt(def, _) if def.is_manually_drop() => {}
-
-                // These types are built-in, so we can fast-track by registering
-                // nested predicates for their constituent type(s)
-                ty::Array(ty, _) | ty::Slice(ty) | ty::Pat(ty, _) => {
-                    stack.push(ty);
-                }
-                ty::Tuple(tys) => {
-                    stack.extend(tys.iter());
-                }
-                ty::Closure(_, args) => {
-                    stack.push(args.as_closure().tupled_upvars_ty());
-                }
-                ty::Coroutine(_, args) => {
-                    let coroutine = args.as_coroutine();
-                    stack.extend([coroutine.tupled_upvars_ty(), coroutine.witness()]);
-                }
-                ty::CoroutineWitness(def_id, args) => {
-                    let tcx = self.tcx();
-                    stack.extend(tcx.bound_coroutine_hidden_types(def_id).map(|bty| {
-                        self.infcx.enter_forall_and_leak_universe(bty.instantiate(tcx, args))
-                    }))
-                }
-
-                // If we have a projection type, make sure to normalize it so we replace it
-                // with a fresh infer variable
-                ty::Alias(ty::Projection | ty::Inherent, ..) => {
-                    let predicate = normalize_with_depth_to(
-                        self,
-                        obligation.param_env,
-                        cause.clone(),
-                        obligation.recursion_depth + 1,
-                        self_ty.rebind(ty::TraitPredicate {
-                            trait_ref: ty::TraitRef::new(
-                                self.tcx(),
-                                self.tcx().require_lang_item(LangItem::Destruct, Some(cause.span)),
-                                [nested_ty.into(), host_effect_param],
-                            ),
-                            polarity: ty::PredicatePolarity::Positive,
-                        }),
-                        &mut nested,
-                    );
-
-                    nested.push(Obligation::with_depth(
-                        tcx,
-                        cause.clone(),
-                        obligation.recursion_depth + 1,
-                        obligation.param_env,
-                        predicate,
-                    ));
-                }
-
-                // If we have any other type (e.g. an ADT), just register a nested obligation
-                // since it's either not `const Drop` (and we raise an error during selection),
-                // or it's an ADT (and we need to check for a custom impl during selection)
-                ty::Error(_)
-                | ty::Dynamic(..)
-                | ty::CoroutineClosure(..)
-                | ty::Param(_)
-                | ty::Bound(..)
-                | ty::Adt(..)
-                | ty::Alias(ty::Opaque | ty::Weak, _)
-                | ty::Infer(_)
-                | ty::Placeholder(_) => {
-                    let predicate = self_ty.rebind(ty::TraitPredicate {
-                        trait_ref: ty::TraitRef::new(
-                            self.tcx(),
-                            self.tcx().require_lang_item(LangItem::Destruct, Some(cause.span)),
-                            [nested_ty.into(), host_effect_param],
-                        ),
-                        polarity: ty::PredicatePolarity::Positive,
-                    });
-
-                    nested.push(Obligation::with_depth(
-                        tcx,
-                        cause.clone(),
-                        obligation.recursion_depth + 1,
-                        obligation.param_env,
-                        predicate,
-                    ));
-                }
-            }
-        }
-
-        Ok(nested)
-    }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 621babe9104..4757430a21c 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1831,12 +1831,8 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             (TransmutabilityCandidate, _) | (_, TransmutabilityCandidate) => DropVictim::No,
 
             // (*)
-            (BuiltinCandidate { has_nested: false } | ConstDestructCandidate(_), _) => {
-                DropVictim::Yes
-            }
-            (_, BuiltinCandidate { has_nested: false } | ConstDestructCandidate(_)) => {
-                DropVictim::No
-            }
+            (BuiltinCandidate { has_nested: false }, _) => DropVictim::Yes,
+            (_, BuiltinCandidate { has_nested: false }) => DropVictim::No,
 
             (ParamCandidate(other), ParamCandidate(victim)) => {
                 let same_except_bound_vars = other.skip_binder().trait_ref
@@ -1855,11 +1851,6 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                 }
             }
 
-            // Drop otherwise equivalent non-const fn pointer candidates
-            (FnPointerCandidate { .. }, FnPointerCandidate { fn_host_effect }) => {
-                DropVictim::drop_if(*fn_host_effect == self.tcx().consts.true_)
-            }
-
             (
                 ParamCandidate(other_cand),
                 ImplCandidate(..)
@@ -2766,7 +2757,6 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         &mut self,
         self_ty: Ty<'tcx>,
         fn_trait_def_id: DefId,
-        fn_host_effect: ty::Const<'tcx>,
     ) -> ty::PolyTraitRef<'tcx> {
         let ty::Closure(_, args) = *self_ty.kind() else {
             bug!("expected closure, found {self_ty}");
@@ -2779,7 +2769,6 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             self_ty,
             closure_sig,
             util::TupleArgumentsFlag::No,
-            fn_host_effect,
         )
         .map_bound(|(trait_ref, _)| trait_ref)
     }
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index aed2e3d61aa..b7a2f20b769 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -215,22 +215,13 @@ pub(crate) fn closure_trait_ref_and_return_type<'tcx>(
     self_ty: Ty<'tcx>,
     sig: ty::PolyFnSig<'tcx>,
     tuple_arguments: TupleArgumentsFlag,
-    fn_host_effect: ty::Const<'tcx>,
 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
     assert!(!self_ty.has_escaping_bound_vars());
     let arguments_tuple = match tuple_arguments {
         TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
         TupleArgumentsFlag::Yes => Ty::new_tup(tcx, sig.skip_binder().inputs()),
     };
-    let trait_ref = if tcx.has_host_param(fn_trait_def_id) {
-        ty::TraitRef::new(tcx, fn_trait_def_id, [
-            ty::GenericArg::from(self_ty),
-            ty::GenericArg::from(arguments_tuple),
-            ty::GenericArg::from(fn_host_effect),
-        ])
-    } else {
-        ty::TraitRef::new(tcx, fn_trait_def_id, [self_ty, arguments_tuple])
-    };
+    let trait_ref = ty::TraitRef::new(tcx, fn_trait_def_id, [self_ty, arguments_tuple]);
     sig.map_bound(|sig| (trait_ref, sig.output()))
 }
 
diff --git a/src/tools/clippy/clippy_lints/src/implied_bounds_in_impls.rs b/src/tools/clippy/clippy_lints/src/implied_bounds_in_impls.rs
index f4c00d8287d..00f83237224 100644
--- a/src/tools/clippy/clippy_lints/src/implied_bounds_in_impls.rs
+++ b/src/tools/clippy/clippy_lints/src/implied_bounds_in_impls.rs
@@ -190,15 +190,6 @@ fn is_same_generics<'tcx>(
         .enumerate()
         .skip(1) // skip `Self` implicit arg
         .all(|(arg_index, arg)| {
-            if [
-                implied_by_generics.host_effect_index,
-                implied_generics.host_effect_index,
-            ]
-            .contains(&Some(arg_index))
-            {
-                // skip host effect params in determining whether generics are same
-                return true;
-            }
             if let Some(ty) = arg.as_type() {
                 if let &ty::Param(ty::ParamTy { index, .. }) = ty.kind()
                     // `index == 0` means that it's referring to `Self`,
diff --git a/src/tools/clippy/clippy_utils/src/ty.rs b/src/tools/clippy/clippy_utils/src/ty.rs
index b7a3569ccf0..cab16b4927d 100644
--- a/src/tools/clippy/clippy_utils/src/ty.rs
+++ b/src/tools/clippy/clippy_utils/src/ty.rs
@@ -274,23 +274,10 @@ pub fn implements_trait_with_env_from_iter<'tcx>(
         .map(|arg| arg.into().unwrap_or_else(|| infcx.next_ty_var(DUMMY_SP).into()))
         .collect::<Vec<_>>();
 
-    // If an effect arg was not specified, we need to specify it.
-    let effect_arg = if tcx
-        .generics_of(trait_id)
-        .host_effect_index
-        .is_some_and(|x| args.get(x - 1).is_none())
-    {
-        Some(GenericArg::from(callee_id.map_or(tcx.consts.true_, |def_id| {
-            tcx.expected_host_effect_param_for_body(def_id)
-        })))
-    } else {
-        None
-    };
-
     let trait_ref = TraitRef::new(
         tcx,
         trait_id,
-        [GenericArg::from(ty)].into_iter().chain(args).chain(effect_arg),
+        [GenericArg::from(ty)].into_iter().chain(args),
     );
 
     debug_assert_matches!(