Revert "Mark DoubleEndedIterator as #[const_trait] using rustc_do_not_const_check, implement const Iterator and DoubleEndedIterator for Range."

This reverts commit 8a9d6bf4fd.

library/core/src/iter/range.rs

@@ -1,5 +1,4 @@
 use crate::convert::TryFrom;
-use crate::marker::Destruct;
 use crate::mem;
 use crate::num::NonZeroUsize;
 use crate::ops::{self, Try};
@@ -524,7 +523,6 @@ macro_rules! range_incl_exact_iter_impl {
 }
 
 /// Specialization implementations for `Range`.
-#[const_trait]
 trait RangeIteratorImpl {
     type Item;
 
@@ -539,7 +537,7 @@ trait RangeIteratorImpl {
     fn spec_advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize>;
 }
 
-impl<A: ~const Step + ~const Destruct> const RangeIteratorImpl for ops::Range<A> {
+impl<A: Step> RangeIteratorImpl for ops::Range<A> {
     type Item = A;
 
     #[inline]
@@ -625,7 +623,7 @@ impl<A: ~const Step + ~const Destruct> const RangeIteratorImpl for ops::Range<A>
     }
 }
 
-impl<T: ~const TrustedStep + ~const Destruct> const RangeIteratorImpl for ops::Range<T> {
+impl<T: TrustedStep> RangeIteratorImpl for ops::Range<T> {
     #[inline]
     fn spec_next(&mut self) -> Option<T> {
         if self.start < self.end {
@@ -713,8 +711,7 @@ impl<T: ~const TrustedStep + ~const Destruct> const RangeIteratorImpl for ops::R
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_iter", issue = "92476")]
-impl<A: ~const Step + ~const Destruct> const Iterator for ops::Range<A> {
+impl<A: Step> Iterator for ops::Range<A> {
     type Item = A;
 
     #[inline]
@@ -824,8 +821,7 @@ range_incl_exact_iter_impl! {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_iter", issue = "92476")]
-impl<A: ~const Step + ~const Destruct> const DoubleEndedIterator for ops::Range<A> {
+impl<A: Step> DoubleEndedIterator for ops::Range<A> {
     #[inline]
     fn next_back(&mut self) -> Option<A> {
         self.spec_next_back()

library/core/src/iter/traits/double_ended.rs

@@ -1,4 +1,3 @@
-use crate::marker::Destruct;
 use crate::num::NonZeroUsize;
 use crate::ops::{ControlFlow, Try};
 
@@ -39,7 +38,6 @@ use crate::ops::{ControlFlow, Try};
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "DoubleEndedIterator")]
-#[const_trait]
 pub trait DoubleEndedIterator: Iterator {
     /// Removes and returns an element from the end of the iterator.
     ///
@@ -136,10 +134,7 @@ pub trait DoubleEndedIterator: Iterator {
     /// [`Err(k)`]: Err
     #[inline]
     #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "77404")]
-    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize>
-    where
-        Self::Item: ~const Destruct,
-    {
+    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
         for i in 0..n {
             if self.next_back().is_none() {
                 // SAFETY: `i` is always less than `n`.
@@ -192,7 +187,6 @@ pub trait DoubleEndedIterator: Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_nth_back", since = "1.37.0")]
-    #[rustc_do_not_const_check]
     fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
         if self.advance_back_by(n).is_err() {
             return None;
@@ -232,7 +226,6 @@ pub trait DoubleEndedIterator: Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iterator_try_fold", since = "1.27.0")]
-    #[rustc_do_not_const_check]
     fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R
     where
         Self: Sized,
@@ -304,7 +297,6 @@ pub trait DoubleEndedIterator: Iterator {
     #[doc(alias = "foldr")]
     #[inline]
     #[stable(feature = "iter_rfold", since = "1.27.0")]
-    #[rustc_do_not_const_check]
     fn rfold<B, F>(mut self, init: B, mut f: F) -> B
     where
         Self: Sized,
@@ -360,7 +352,6 @@ pub trait DoubleEndedIterator: Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_rfind", since = "1.27.0")]
-    #[rustc_do_not_const_check]
     fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
     where
         Self: Sized,

library/core/src/iter/traits/iterator.rs

@@ -1,6 +1,5 @@
 use crate::array;
 use crate::cmp::{self, Ordering};
-use crate::marker::Destruct;
 use crate::num::NonZeroUsize;
 use crate::ops::{ChangeOutputType, ControlFlow, FromResidual, Residual, Try};
 
@@ -340,10 +339,8 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "77404")]
-    fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize>
-    where
-        Self::Item: ~const Destruct,
-    {
+    #[rustc_do_not_const_check]
+    fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
         for i in 0..n {
             if self.next().is_none() {
                 // SAFETY: `i` is always less than `n`.
@@ -394,10 +391,8 @@ pub trait Iterator {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    fn nth(&mut self, n: usize) -> Option<Self::Item>
-    where
-        Self::Item: ~const Destruct,
-    {
+    #[rustc_do_not_const_check]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
         self.advance_by(n).ok()?;
         self.next()
     }

library/core/src/lib.rs

@@ -123,7 +123,6 @@
 #![feature(const_index_range_slice_index)]
 #![feature(const_inherent_unchecked_arith)]
 #![feature(const_int_unchecked_arith)]
-#![feature(const_intoiterator_identity)]
 #![feature(const_intrinsic_forget)]
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]

library/core/tests/iter/consts.rs

@@ -1,36 +0,0 @@
-#[test]
-fn const_manual_iter() {
-    struct S(bool);
-
-    impl const Iterator for S {
-        type Item = ();
-
-        fn next(&mut self) -> Option<Self::Item> {
-            if self.0 == false {
-                self.0 = true;
-                Some(())
-            } else {
-                None
-            }
-        }
-    }
-    const {
-        let mut val = S(false);
-        assert!(val.next().is_some());
-        assert!(val.next().is_none());
-        assert!(val.next().is_none());
-    }
-}
-
-#[test]
-fn const_range() {
-    const {
-        let mut arr = [0; 3];
-        for i in 0..arr.len() {
-            arr[i] = i;
-        }
-        assert!(arr[0] == 0);
-        assert!(arr[1] == 1);
-        assert!(arr[2] == 2);
-    }
-}

library/core/tests/iter/mod.rs

@@ -20,8 +20,6 @@ mod range;
 mod sources;
 mod traits;
 
-mod consts;
-
 use core::cell::Cell;
 use core::convert::TryFrom;
 use core::iter::*;

library/core/tests/lib.rs

@@ -12,11 +12,8 @@
 #![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
 #![feature(const_convert)]
-#![feature(const_for)]
 #![feature(const_hash)]
 #![feature(const_heap)]
-#![feature(const_intoiterator_identity)]
-#![feature(const_iter)]
 #![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_assume_init_read)]
 #![feature(const_nonnull_new)]

tests/ui/typeck/typeck_type_placeholder_item.rs

@@ -228,4 +228,5 @@ fn evens_squared(n: usize) -> _ {
 
 const _: _ = (1..10).filter(|x| x % 2 == 0).map(|x| x * x);
 //~^ ERROR the trait bound
+//~| ERROR the trait bound
 //~| ERROR the placeholder

tests/ui/typeck/typeck_type_placeholder_item.stderr

@@ -437,6 +437,19 @@ 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
    |
@@ -664,7 +677,7 @@ LL |     const D: _ = 42;
    |              not allowed in type signatures
    |              help: replace with the correct type: `i32`
 
-error: aborting due to 72 previous errors
+error: aborting due to 73 previous errors
 
 Some errors have detailed explanations: E0121, E0277, E0282, E0403.
 For more information about an error, try `rustc --explain E0121`.