1 files changed, 5 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index 111b1d009b3..4d5f5b8658c 100644
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -11,6 +11,7 @@ use rustc_errors::{DiagnosticArgValue, IntoDiagnosticArg};
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
 use rustc_serialize::{self, Decodable, Encodable};
+use rustc_span::sym;
 use rustc_type_ir::WithCachedTypeInfo;
 use smallvec::SmallVec;
 
@@ -451,6 +452,10 @@ impl<'tcx> InternalSubsts<'tcx> {
     pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> {
         tcx.mk_substs_from_iter(self.iter().take(generics.count()))
     }
+
+    pub fn host_effect_param(&'tcx self) -> Option<ty::Const<'tcx>> {
+        self.consts().rfind(|x| matches!(x.kind(), ty::ConstKind::Param(p) if p.name == sym::host))
+    }
 }
 
 impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for SubstsRef<'tcx> {