Add helper for when we want to know if an item has a host param

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -157,9 +157,7 @@ impl Qualif for NeedsNonConstDrop {
  // 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.generics_of(destruct_def_id).host_effect_index.is_none()
- || !cx.tcx.features().effects
- {
+ if !cx.tcx.has_host_param(destruct_def_id) || !cx.tcx.features().effects {
  return NeedsDrop::in_any_value_of_ty(cx, ty);
  }
 

compiler/rustc_hir_typeck/src/callee.rs

@@ -490,11 +490,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  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.generics_of(fn_once_def_id).host_effect_index.is_none() {
- if idx == 0 && !self.tcx.is_const_fn_raw(def_id) {
- self.dcx().emit_err(errors::ConstSelectMustBeConst { span });
- }
- } else {
+ 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(
@@ -523,6 +519,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  ));
 
  self.select_obligations_where_possible(|_| {});
+ } else if idx == 0 && !self.tcx.is_const_fn_raw(def_id) {
+ self.dcx().emit_err(errors::ConstSelectMustBeConst { span });
  }
  } else {
  self.dcx().emit_err(errors::ConstSelectMustBeFn { span, ty: arg_ty });

compiler/rustc_middle/src/ty/util.rs

@@ -1,7 +1,7 @@
 //! Miscellaneous type-system utilities that are too small to deserve their own modules.
 
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
-use crate::query::Providers;
+use crate::query::{IntoQueryParam, Providers};
 use crate::ty::layout::IntegerExt;
 use crate::ty::{
  self, FallibleTypeFolder, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
@@ -786,6 +786,13 @@ impl<'tcx> TyCtxt<'tcx> {
  || self.extern_crate(key.as_def_id()).is_some_and(|e| e.is_direct())
  }
 
+ /// Whether the item has a host effect param. This is different from `TyCtxt::is_const`,
+ /// because the item must also be "maybe const", and the crate where the item is
+ /// defined must also have the effects feature enabled.
+ pub fn has_host_param(self, def_id: impl IntoQueryParam<DefId>) -> bool {
+ self.generics_of(def_id).host_effect_index.is_some()
+ }
+
  pub fn expected_host_effect_param_for_body(self, def_id: impl Into<DefId>) -> ty::Const<'tcx> {
  let def_id = def_id.into();
  // FIXME(effects): This is suspicious and should probably not be done,

compiler/rustc_trait_selection/src/traits/util.rs

@@ -271,7 +271,7 @@ pub fn closure_trait_ref_and_return_type<'tcx>(
  TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
  TupleArgumentsFlag::Yes => Ty::new_tup(tcx, sig.skip_binder().inputs()),
  };
- let trait_ref = if tcx.generics_of(fn_trait_def_id).host_effect_index.is_some() {
+ let trait_ref = if tcx.has_host_param(fn_trait_def_id) {
  ty::TraitRef::new(
  tcx,
  fn_trait_def_id,