implement const iterator using `rustc_do_not_const_check`

4 files changed, 101 insertions, 1 deletions

diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index 323bacf70ab..651b3114484 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -67,7 +67,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::config;
 use rustc_session::Session;
 use rustc_span::def_id::{DefId, LocalDefId};
-use rustc_span::Span;
+use rustc_span::{sym, Span};
 
 #[macro_export]
 macro_rules! type_error_struct {
@@ -201,6 +201,11 @@ fn typeck_with_fallback<'tcx>(
 
     let typeck_results = Inherited::build(tcx, def_id).enter(|inh| {
         let param_env = tcx.param_env(def_id);
+        let param_env = if tcx.has_attr(def_id.to_def_id(), sym::rustc_do_not_const_check) {
+            param_env.without_const()
+        } else {
+            param_env
+        };
         let mut fcx = FnCtxt::new(&inh, param_env, def_id);
 
         if let Some(hir::FnSig { header, decl, .. }) = fn_sig {
diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
index 5a0b8594104..357c8082762 100644
--- a/library/core/src/iter/traits/iterator.rs
+++ b/library/core/src/iter/traits/iterator.rs
@@ -69,6 +69,7 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
 #[doc(notable_trait)]
 #[rustc_diagnostic_item = "Iterator"]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Iterator {
     /// The type of the elements being iterated over.
     #[rustc_diagnostic_item = "IteratorItem"]
@@ -141,6 +142,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iter_next_chunk", reason = "recently added", issue = "98326")]
+    #[rustc_do_not_const_check]
     fn next_chunk<const N: usize>(
         &mut self,
     ) -> Result<[Self::Item; N], array::IntoIter<Self::Item, N>>
@@ -218,6 +220,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn size_hint(&self) -> (usize, Option<usize>) {
         (0, None)
     }
@@ -255,6 +258,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn count(self) -> usize
     where
         Self: Sized,
@@ -285,6 +289,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn last(self) -> Option<Self::Item>
     where
         Self: Sized,
@@ -331,6 +336,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "77404")]
+    #[rustc_do_not_const_check]
     fn advance_by(&mut self, n: usize) -> Result<(), usize> {
         for i in 0..n {
             self.next().ok_or(i)?;
@@ -379,6 +385,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn nth(&mut self, n: usize) -> Option<Self::Item> {
         self.advance_by(n).ok()?;
         self.next()
@@ -431,6 +438,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_step_by", since = "1.28.0")]
+    #[rustc_do_not_const_check]
     fn step_by(self, step: usize) -> StepBy<Self>
     where
         Self: Sized,
@@ -502,6 +510,7 @@ pub trait Iterator {
     /// [`OsStr`]: ../../std/ffi/struct.OsStr.html
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter>
     where
         Self: Sized,
@@ -620,6 +629,7 @@ pub trait Iterator {
     /// [`zip`]: crate::iter::zip
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter>
     where
         Self: Sized,
@@ -662,6 +672,7 @@ pub trait Iterator {
     /// [`intersperse_with`]: Iterator::intersperse_with
     #[inline]
     #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
+    #[rustc_do_not_const_check]
     fn intersperse(self, separator: Self::Item) -> Intersperse<Self>
     where
         Self: Sized,
@@ -720,6 +731,7 @@ pub trait Iterator {
     /// [`intersperse`]: Iterator::intersperse
     #[inline]
     #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
+    #[rustc_do_not_const_check]
     fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G>
     where
         Self: Sized,
@@ -779,6 +791,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn map<B, F>(self, f: F) -> Map<Self, F>
     where
         Self: Sized,
@@ -824,6 +837,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_for_each", since = "1.21.0")]
+    #[rustc_do_not_const_check]
     fn for_each<F>(self, f: F)
     where
         Self: Sized,
@@ -899,6 +913,7 @@ pub trait Iterator {
     /// Note that `iter.filter(f).next()` is equivalent to `iter.find(f)`.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn filter<P>(self, predicate: P) -> Filter<Self, P>
     where
         Self: Sized,
@@ -944,6 +959,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
     where
         Self: Sized,
@@ -990,6 +1006,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn enumerate(self) -> Enumerate<Self>
     where
         Self: Sized,
@@ -1061,6 +1078,7 @@ pub trait Iterator {
     /// [`next`]: Iterator::next
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn peekable(self) -> Peekable<Self>
     where
         Self: Sized,
@@ -1126,6 +1144,7 @@ pub trait Iterator {
     #[inline]
     #[doc(alias = "drop_while")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
     where
         Self: Sized,
@@ -1207,6 +1226,7 @@ pub trait Iterator {
     /// the iteration should stop, but wasn't placed back into the iterator.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>
     where
         Self: Sized,
@@ -1295,6 +1315,7 @@ pub trait Iterator {
     /// [`fuse`]: Iterator::fuse
     #[inline]
     #[stable(feature = "iter_map_while", since = "1.57.0")]
+    #[rustc_do_not_const_check]
     fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P>
     where
         Self: Sized,
@@ -1326,6 +1347,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn skip(self, n: usize) -> Skip<Self>
     where
         Self: Sized,
@@ -1379,6 +1401,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn take(self, n: usize) -> Take<Self>
     where
         Self: Sized,
@@ -1428,6 +1451,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
     where
         Self: Sized,
@@ -1468,6 +1492,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
     where
         Self: Sized,
@@ -1552,6 +1577,7 @@ pub trait Iterator {
     /// [`flat_map()`]: Iterator::flat_map
     #[inline]
     #[stable(feature = "iterator_flatten", since = "1.29.0")]
+    #[rustc_do_not_const_check]
     fn flatten(self) -> Flatten<Self>
     where
         Self: Sized,
@@ -1620,6 +1646,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn fuse(self) -> Fuse<Self>
     where
         Self: Sized,
@@ -1704,6 +1731,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn inspect<F>(self, f: F) -> Inspect<Self, F>
     where
         Self: Sized,
@@ -1734,6 +1762,7 @@ pub trait Iterator {
     /// assert_eq!(of_rust, vec!["of", "Rust"]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn by_ref(&mut self) -> &mut Self
     where
         Self: Sized,
@@ -1853,6 +1882,7 @@ pub trait Iterator {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]
     #[cfg_attr(not(test), rustc_diagnostic_item = "iterator_collect_fn")]
+    #[rustc_do_not_const_check]
     fn collect<B: FromIterator<Self::Item>>(self) -> B
     where
         Self: Sized,
@@ -1931,6 +1961,7 @@ pub trait Iterator {
     /// [`collect`]: Iterator::collect
     #[inline]
     #[unstable(feature = "iterator_try_collect", issue = "94047")]
+    #[rustc_do_not_const_check]
     fn try_collect<B>(&mut self) -> ChangeOutputType<Self::Item, B>
     where
         Self: Sized,
@@ -2004,6 +2035,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iter_collect_into", reason = "new API", issue = "94780")]
+    #[rustc_do_not_const_check]
     fn collect_into<E: Extend<Self::Item>>(self, collection: &mut E) -> &mut E
     where
         Self: Sized,
@@ -2038,6 +2070,7 @@ pub trait Iterator {
     /// assert_eq!(odd, vec![1, 3]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn partition<B, F>(self, f: F) -> (B, B)
     where
         Self: Sized,
@@ -2100,6 +2133,7 @@ pub trait Iterator {
     /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds
     /// ```
     #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")]
+    #[rustc_do_not_const_check]
     fn partition_in_place<'a, T: 'a, P>(mut self, ref mut predicate: P) -> usize
     where
         Self: Sized + DoubleEndedIterator<Item = &'a mut T>,
@@ -2157,6 +2191,7 @@ pub trait Iterator {
     /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase));
     /// ```
     #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")]
+    #[rustc_do_not_const_check]
     fn is_partitioned<P>(mut self, mut predicate: P) -> bool
     where
         Self: Sized,
@@ -2251,6 +2286,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_try_fold", since = "1.27.0")]
+    #[rustc_do_not_const_check]
     fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R
     where
         Self: Sized,
@@ -2309,6 +2345,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_try_fold", since = "1.27.0")]
+    #[rustc_do_not_const_check]
     fn try_for_each<F, R>(&mut self, f: F) -> R
     where
         Self: Sized,
@@ -2428,6 +2465,7 @@ pub trait Iterator {
     #[doc(alias = "inject", alias = "foldl")]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn fold<B, F>(mut self, init: B, mut f: F) -> B
     where
         Self: Sized,
@@ -2465,6 +2503,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_fold_self", since = "1.51.0")]
+    #[rustc_do_not_const_check]
     fn reduce<F>(mut self, f: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -2536,6 +2575,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iterator_try_reduce", reason = "new API", issue = "87053")]
+    #[rustc_do_not_const_check]
     fn try_reduce<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<R::Output>>
     where
         Self: Sized,
@@ -2593,6 +2633,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn all<F>(&mut self, f: F) -> bool
     where
         Self: Sized,
@@ -2646,6 +2687,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn any<F>(&mut self, f: F) -> bool
     where
         Self: Sized,
@@ -2709,6 +2751,7 @@ pub trait Iterator {
     /// Note that `iter.find(f)` is equivalent to `iter.filter(f).next()`.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
     where
         Self: Sized,
@@ -2740,6 +2783,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_find_map", since = "1.30.0")]
+    #[rustc_do_not_const_check]
     fn find_map<B, F>(&mut self, f: F) -> Option<B>
     where
         Self: Sized,
@@ -2796,6 +2840,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "try_find", reason = "new API", issue = "63178")]
+    #[rustc_do_not_const_check]
     fn try_find<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<Self::Item>>
     where
         Self: Sized,
@@ -2878,6 +2923,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn position<P>(&mut self, predicate: P) -> Option<usize>
     where
         Self: Sized,
@@ -2935,6 +2981,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn rposition<P>(&mut self, predicate: P) -> Option<usize>
     where
         P: FnMut(Self::Item) -> bool,
@@ -2986,6 +3033,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn max(self) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3024,6 +3072,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn min(self) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3046,6 +3095,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
+    #[rustc_do_not_const_check]
     fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3079,6 +3129,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_max_by", since = "1.15.0")]
+    #[rustc_do_not_const_check]
     fn max_by<F>(self, compare: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3106,6 +3157,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
+    #[rustc_do_not_const_check]
     fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3139,6 +3191,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_min_by", since = "1.15.0")]
+    #[rustc_do_not_const_check]
     fn min_by<F>(self, compare: F) -> Option<Self::Item>
     where
         Self: Sized,
@@ -3176,6 +3229,7 @@ pub trait Iterator {
     #[inline]
     #[doc(alias = "reverse")]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn rev(self) -> Rev<Self>
     where
         Self: Sized + DoubleEndedIterator,
@@ -3214,6 +3268,7 @@ pub trait Iterator {
     /// assert_eq!(z, [3, 6]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
     where
         FromA: Default + Extend<A>,
@@ -3246,6 +3301,7 @@ pub trait Iterator {
     /// assert_eq!(v_map, vec![1, 2, 3]);
     /// ```
     #[stable(feature = "iter_copied", since = "1.36.0")]
+    #[rustc_do_not_const_check]
     fn copied<'a, T: 'a>(self) -> Copied<Self>
     where
         Self: Sized + Iterator<Item = &'a T>,
@@ -3293,6 +3349,7 @@ pub trait Iterator {
     /// assert_eq!(&[vec![23]], &faster[..]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_do_not_const_check]
     fn cloned<'a, T: 'a>(self) -> Cloned<Self>
     where
         Self: Sized + Iterator<Item = &'a T>,
@@ -3327,6 +3384,7 @@ pub trait Iterator {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
+    #[rustc_do_not_const_check]
     fn cycle(self) -> Cycle<Self>
     where
         Self: Sized + Clone,
@@ -3370,6 +3428,7 @@ pub trait Iterator {
     /// ```
     #[track_caller]
     #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "100450")]
+    #[rustc_do_not_const_check]
     fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N>
     where
         Self: Sized,
@@ -3400,6 +3459,7 @@ pub trait Iterator {
     /// assert_eq!(sum, 6);
     /// ```
     #[stable(feature = "iter_arith", since = "1.11.0")]
+    #[rustc_do_not_const_check]
     fn sum<S>(self) -> S
     where
         Self: Sized,
@@ -3429,6 +3489,7 @@ pub trait Iterator {
     /// assert_eq!(factorial(5), 120);
     /// ```
     #[stable(feature = "iter_arith", since = "1.11.0")]
+    #[rustc_do_not_const_check]
     fn product<P>(self) -> P
     where
         Self: Sized,
@@ -3450,6 +3511,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn cmp<I>(self, other: I) -> Ordering
     where
         I: IntoIterator<Item = Self::Item>,
@@ -3479,6 +3541,7 @@ pub trait Iterator {
     /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater);
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
+    #[rustc_do_not_const_check]
     fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
     where
         Self: Sized,
@@ -3517,6 +3580,7 @@ pub trait Iterator {
     /// assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn partial_cmp<I>(self, other: I) -> Option<Ordering>
     where
         I: IntoIterator,
@@ -3555,6 +3619,7 @@ pub trait Iterator {
     /// );
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
+    #[rustc_do_not_const_check]
     fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
     where
         Self: Sized,
@@ -3588,6 +3653,7 @@ pub trait Iterator {
     /// assert_eq!([1].iter().eq([1, 2].iter()), false);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn eq<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3613,6 +3679,7 @@ pub trait Iterator {
     /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y));
     /// ```
     #[unstable(feature = "iter_order_by", issue = "64295")]
+    #[rustc_do_not_const_check]
     fn eq_by<I, F>(self, other: I, eq: F) -> bool
     where
         Self: Sized,
@@ -3645,6 +3712,7 @@ pub trait Iterator {
     /// assert_eq!([1].iter().ne([1, 2].iter()), true);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn ne<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3666,6 +3734,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().lt([1, 2].iter()), false);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn lt<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3687,6 +3756,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().le([1, 2].iter()), true);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn le<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3708,6 +3778,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().gt([1, 2].iter()), false);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn gt<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3729,6 +3800,7 @@ pub trait Iterator {
     /// assert_eq!([1, 2].iter().ge([1, 2].iter()), true);
     /// ```
     #[stable(feature = "iter_order", since = "1.5.0")]
+    #[rustc_do_not_const_check]
     fn ge<I>(self, other: I) -> bool
     where
         I: IntoIterator,
@@ -3760,6 +3832,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[rustc_do_not_const_check]
     fn is_sorted(self) -> bool
     where
         Self: Sized,
@@ -3788,6 +3861,7 @@ pub trait Iterator {
     ///
     /// [`is_sorted`]: Iterator::is_sorted
     #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[rustc_do_not_const_check]
     fn is_sorted_by<F>(mut self, compare: F) -> bool
     where
         Self: Sized,
@@ -3834,6 +3908,7 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
+    #[rustc_do_not_const_check]
     fn is_sorted_by_key<F, K>(self, f: F) -> bool
     where
         Self: Sized,
@@ -3849,6 +3924,7 @@ pub trait Iterator {
     #[inline]
     #[doc(hidden)]
     #[unstable(feature = "trusted_random_access", issue = "none")]
+    #[rustc_do_not_const_check]
     unsafe fn __iterator_get_unchecked(&mut self, _idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccessNoCoerce,
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 6dfe36e6926..3528ef0a3e5 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -194,6 +194,7 @@
 #![feature(cfg_target_has_atomic_equal_alignment)]
 #![cfg_attr(not(bootstrap), feature(const_closures))]
 #![feature(const_fn_floating_point_arithmetic)]
+#![feature(const_for)]
 #![feature(const_mut_refs)]
 #![feature(const_precise_live_drops)]
 #![feature(const_refs_to_cell)]
diff --git a/tests/ui/rfc-2632-const-trait-impl/do-not-const-check.rs b/tests/ui/rfc-2632-const-trait-impl/do-not-const-check.rs
new file mode 100644
index 00000000000..3c39c53de5f
--- /dev/null
+++ b/tests/ui/rfc-2632-const-trait-impl/do-not-const-check.rs
@@ -0,0 +1,18 @@
+// check-pass
+#![feature(const_trait_impl, rustc_attrs)]
+
+#[const_trait]
+trait IntoIter {
+    fn into_iter(self);
+}
+
+#[const_trait]
+trait Hmm: Sized {
+    #[rustc_do_not_const_check]
+    fn chain<U>(self, other: U) where U: IntoIter,
+    {
+        other.into_iter()
+    }
+}
+
+fn main() {}