Rollup merge of #106541 - fee1-dead-contrib:no-const-check-no, r=thomcc

implement const iterator using `rustc_do_not_const_check` Previous experiment: #102225. Explanation: rather than making all default methods work under `const` all at once, this uses `rustc_do_not_const_check` as a workaround to "trick" the compiler to not run any checks on those other default methods. Any const implementations are only required to implement the `next` method. Any actual calls to the trait methods other than `next` will either error in compile time (at CTFE runs), or run the methods correctly if they do not have any non-const operations. This is extremely easy to maintain, remove, or improve.
2023-02-24 12:02:40 +05:30 · 2023-02-24 12:02:40 +05:30 · 8c135eecac
commit 8c135eecac
parent 07c993eba8 3aeb43cb78
9 changed files with 167 additions and 10 deletions
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@ -71,7 +71,7 @@ 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};

 fluent_messages! { "../locales/en-US.ftl" }

@ -207,6 +207,11 @@ 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 {
--- 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,
@ -3535,6 +3598,7 @@ pub trait Iterator {
    /// ```
    ///
    #[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,
@ -3573,6 +3637,7 @@ 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,
@ -3606,6 +3671,7 @@ 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,
@ -3631,6 +3697,7 @@ 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,
@ -3663,6 +3730,7 @@ 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,
@ -3684,6 +3752,7 @@ 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,
@ -3705,6 +3774,7 @@ 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,
@ -3726,6 +3796,7 @@ 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,
@ -3747,6 +3818,7 @@ 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,
@ -3778,6 +3850,7 @@ 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,
@ -3806,6 +3879,7 @@ 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,
@ -3852,6 +3926,7 @@ 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,
@ -3867,6 +3942,7 @@ 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,
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@ -194,6 +194,7 @@
 #![feature(cfg_target_has_atomic_equal_alignment)]
 #![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)]
--- a/tests/ui/consts/gate-do-not-const-check.rs
+++ b/tests/ui/consts/gate-do-not-const-check.rs
@ -0,0 +1,5 @@
+#[rustc_do_not_const_check]
+//~^ ERROR this is an internal attribute that will never be stable
+const fn foo() {}
+
+fn main() {}
--- a/tests/ui/consts/gate-do-not-const-check.stderr
+++ b/tests/ui/consts/gate-do-not-const-check.stderr
@ -0,0 +1,11 @@
+error[E0658]: this is an internal attribute that will never be stable
+  --> $DIR/gate-do-not-const-check.rs:1:1
+   |
+LL | #[rustc_do_not_const_check]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.
--- a/tests/ui/rfc-2632-const-trait-impl/do-not-const-check-override.rs
+++ b/tests/ui/rfc-2632-const-trait-impl/do-not-const-check-override.rs
@ -0,0 +1,19 @@
+// check-pass
+#![feature(const_trait_impl, rustc_attrs)]
+
+#[const_trait]
+trait Foo {
+    #[rustc_do_not_const_check]
+    fn into_iter(&self) { println!("FEAR ME!") }
+}
+
+
+impl const Foo for () {
+    fn into_iter(&self) {
+        // ^_^
+    }
+}
+
+const _: () = Foo::into_iter(&());
+
+fn main() {}
--- 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
@ -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() {}
--- a/tests/ui/typeck/typeck_type_placeholder_item.rs
+++ b/tests/ui/typeck/typeck_type_placeholder_item.rs
@ -227,4 +227,6 @@ fn evens_squared(n: usize) -> _ {
 }

 const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
-//~^ ERROR the placeholder `_` is not allowed within types on item signatures for constants
+//~^ ERROR the trait bound
+//~| ERROR the trait bound
+//~| ERROR the placeholder
--- a/tests/ui/typeck/typeck_type_placeholder_item.stderr
+++ b/tests/ui/typeck/typeck_type_placeholder_item.stderr
@ -437,17 +437,37 @@ LL | fn evens_squared(n: usize) -> _ {
   |                               not allowed in type signatures
   |                               help: replace with an appropriate return type: `impl Iterator<Item = usize>`

+error[E0277]: the trait bound `std::ops::Range<{integer}>: Iterator` is not satisfied
+  --> $DIR/typeck_type_placeholder_item.rs:229:22
+   |
+LL | const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
+   |                      ^^^^^^ `std::ops::Range<{integer}>` is not an iterator
+   |
+   = help: the trait `~const Iterator` is not implemented for `std::ops::Range<{integer}>`
+note: the trait `Iterator` is implemented for `std::ops::Range<{integer}>`, but that implementation is not `const`
+  --> $DIR/typeck_type_placeholder_item.rs:229:14
+   |
+LL | const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
+   |              ^^^^^^^
+
+error[E0277]: the trait bound `Filter<std::ops::Range<{integer}>, [closure@$DIR/typeck_type_placeholder_item.rs:229:29: 229:32]>: Iterator` is not satisfied
+  --> $DIR/typeck_type_placeholder_item.rs:229:45
+   |
+LL | const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
+   |                                             ^^^ `Filter<std::ops::Range<{integer}>, [closure@$DIR/typeck_type_placeholder_item.rs:229:29: 229:32]>` is not an iterator
+   |
+   = help: the trait `~const Iterator` is not implemented for `Filter<std::ops::Range<{integer}>, [closure@$DIR/typeck_type_placeholder_item.rs:229:29: 229:32]>`
+note: the trait `Iterator` is implemented for `Filter<std::ops::Range<{integer}>, [closure@$DIR/typeck_type_placeholder_item.rs:229:29: 229:32]>`, but that implementation is not `const`
+  --> $DIR/typeck_type_placeholder_item.rs:229:14
+   |
+LL | const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error[E0121]: the placeholder `_` is not allowed within types on item signatures for constants
  --> $DIR/typeck_type_placeholder_item.rs:229:10
   |
 LL | const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
   |          ^ not allowed in type signatures
-   |
-note: however, the inferred type `Map<Filter<Range<i32>, [closure@typeck_type_placeholder_item.rs:229:29]>, [closure@typeck_type_placeholder_item.rs:229:49]>` cannot be named
-  --> $DIR/typeck_type_placeholder_item.rs:229:14
-   |
-LL | const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 error[E0121]: the placeholder `_` is not allowed within types on item signatures for functions
  --> $DIR/typeck_type_placeholder_item.rs:140:31
@ -657,7 +677,7 @@ LL |     const D: _ = 42;
   |              not allowed in type signatures
   |              help: replace with the correct type: `i32`

-error: aborting due to 71 previous errors
+error: aborting due to 73 previous errors

-Some errors have detailed explanations: E0121, E0282, E0403.
+Some errors have detailed explanations: E0121, E0277, E0282, E0403.
 For more information about an error, try `rustc --explain E0121`.