Introduce subst_iter and subst_iter_copied on EarlyBinder

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -795,8 +795,7 @@ pub trait PrettyPrinter<'tcx>:
         let mut fn_traits = FxIndexMap::default();
         let mut is_sized = false;
 
-        for predicate in bounds.transpose_iter().map(|e| e.map_bound(|(p, _)| *p)) {
-            let predicate = predicate.subst(tcx, substs);
+        for (predicate, _) in bounds.subst_iter_copied(tcx, substs) {
             let bound_predicate = predicate.kind();
 
             match bound_predicate.skip_binder() {

compiler/rustc_middle/src/ty/subst.rs

@@ -6,6 +6,7 @@ use crate::ty::sty::{ClosureSubsts, GeneratorSubsts, InlineConstSubsts};
 use crate::ty::visit::{TypeVisitable, TypeVisitor};
 use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt};
 
+use rustc_data_structures::captures::Captures;
 use rustc_data_structures::intern::{Interned, WithStableHash};
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
@@ -550,6 +551,28 @@ impl<T, U> EarlyBinder<(T, U)> {
     }
 }
 
+impl<'tcx, 's, T: IntoIterator<Item = I>, I: TypeFoldable<'tcx>> EarlyBinder<T> {
+    pub fn subst_iter(
+        self,
+        tcx: TyCtxt<'tcx>,
+        substs: &'s [GenericArg<'tcx>],
+    ) -> impl Iterator<Item = I> + Captures<'s> + Captures<'tcx> {
+        self.0.into_iter().map(move |t| EarlyBinder(t).subst(tcx, substs))
+    }
+}
+
+impl<'tcx, 's, 'a, T: IntoIterator<Item = &'a I>, I: Copy + TypeFoldable<'tcx> + 'a>
+    EarlyBinder<T>
+{
+    pub fn subst_iter_copied(
+        self,
+        tcx: TyCtxt<'tcx>,
+        substs: &'s [GenericArg<'tcx>],
+    ) -> impl Iterator<Item = I> + Captures<'s> + Captures<'tcx> + Captures<'a> {
+        self.0.into_iter().map(move |t| EarlyBinder(*t).subst(tcx, substs))
+    }
+}
+
 pub struct EarlyBinderIter<T> {
     t: T,
 }