Bootstrapping preparation for the library

Since just `ops::Try` will need to change meaning.

Author: scottmcm

library/alloc/src/collections/vec_deque/iter.rs

@@ -1,6 +1,6 @@
 use core::fmt;
 use core::iter::{FusedIterator, TrustedLen, TrustedRandomAccess};
-use core::ops::Try;
+use core::ops::TryWhereOutputEquals;
 
 use super::{count, wrap_index, RingSlices};
 
@@ -66,7 +66,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: TryWhereOutputEquals<B>,
     {
         let (mut iter, final_res);
         if self.tail <= self.head {
@@ -140,7 +140,7 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: TryWhereOutputEquals<B>,
     {
         let (mut iter, final_res);
         if self.tail <= self.head {

library/alloc/src/lib.rs

@@ -141,6 +141,7 @@
 #![feature(alloc_layout_extra)]
 #![feature(trusted_random_access)]
 #![feature(try_trait)]
+#![feature(try_trait_transition)]
 #![feature(min_type_alias_impl_trait)]
 #![feature(associated_type_bounds)]
 #![feature(slice_group_by)]

library/core/src/iter/adapters/chain.rs

@@ -1,5 +1,5 @@
 use crate::iter::{DoubleEndedIterator, FusedIterator, Iterator, TrustedLen};
-use crate::ops::Try;
+use crate::ops::TryWhereOutputEquals;
 
 /// An iterator that links two iterators together, in a chain.
 ///
@@ -98,7 +98,7 @@ where
     where
         Self: Sized,
         F: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         if let Some(ref mut a) = self.a {
             acc = a.try_fold(acc, &mut f)?;
@@ -281,7 +281,7 @@ where
     where
         Self: Sized,
         F: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         if let Some(ref mut b) = self.b {
             acc = b.try_rfold(acc, &mut f)?;

library/core/src/iter/adapters/cloned.rs

@@ -1,6 +1,6 @@
 use crate::iter::adapters::{zip::try_get_unchecked, TrustedRandomAccess};
 use crate::iter::{FusedIterator, TrustedLen};
-use crate::ops::Try;
+use crate::ops::TryWhereOutputEquals;
 
 /// An iterator that clones the elements of an underlying iterator.
 ///
@@ -46,7 +46,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: TryWhereOutputEquals<B>,
     {
         self.it.try_fold(init, clone_try_fold(f))
     }
@@ -82,7 +82,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: TryWhereOutputEquals<B>,
     {
         self.it.try_rfold(init, clone_try_fold(f))
     }

library/core/src/iter/adapters/copied.rs

@@ -1,6 +1,6 @@
 use crate::iter::adapters::{zip::try_get_unchecked, TrustedRandomAccess};
 use crate::iter::{FusedIterator, TrustedLen};
-use crate::ops::Try;
+use crate::ops::TryWhereOutputEquals;
 
 /// An iterator that copies the elements of an underlying iterator.
 ///
@@ -50,7 +50,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: TryWhereOutputEquals<B>,
     {
         self.it.try_fold(init, copy_try_fold(f))
     }
@@ -98,7 +98,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: TryWhereOutputEquals<B>,
     {
         self.it.try_rfold(init, copy_try_fold(f))
     }

library/core/src/iter/adapters/cycle.rs

@@ -1,4 +1,4 @@
-use crate::{iter::FusedIterator, ops::Try};
+use crate::{iter::FusedIterator, ops::TryWhereOutputEquals};
 
 /// An iterator that repeats endlessly.
 ///
@@ -53,7 +53,7 @@ where
     fn try_fold<Acc, F, R>(&mut self, mut acc: Acc, mut f: F) -> R
     where
         F: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         // fully iterate the current iterator. this is necessary because
         // `self.iter` may be empty even when `self.orig` isn't

library/core/src/iter/adapters/enumerate.rs

@@ -1,6 +1,6 @@
 use crate::iter::adapters::{zip::try_get_unchecked, SourceIter, TrustedRandomAccess};
 use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen};
-use crate::ops::Try;
+use crate::ops::TryWhereOutputEquals;
 
 /// An iterator that yields the current count and the element during iteration.
 ///
@@ -71,7 +71,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         #[inline]
         fn enumerate<'a, T, Acc, R>(
@@ -150,7 +150,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         // Can safely add and subtract the count, as `ExactSizeIterator` promises
         // that the number of elements fits into a `usize`.

library/core/src/iter/adapters/filter.rs

@@ -1,6 +1,6 @@
 use crate::fmt;
 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
-use crate::ops::Try;
+use crate::ops::TryWhereOutputEquals;
 
 /// An iterator that filters the elements of `iter` with `predicate`.
 ///
@@ -37,7 +37,7 @@ fn filter_fold<T, Acc>(
     move |acc, item| if predicate(&item) { fold(acc, item) } else { acc }
 }
 
-fn filter_try_fold<'a, T, Acc, R: Try<Ok = Acc>>(
+fn filter_try_fold<'a, T, Acc, R: TryWhereOutputEquals<Acc>>(
     predicate: &'a mut impl FnMut(&T) -> bool,
     mut fold: impl FnMut(Acc, T) -> R + 'a,
 ) -> impl FnMut(Acc, T) -> R + 'a {
@@ -88,7 +88,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.iter.try_fold(init, filter_try_fold(&mut self.predicate, fold))
     }
@@ -117,7 +117,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.iter.try_rfold(init, filter_try_fold(&mut self.predicate, fold))
     }

library/core/src/iter/adapters/filter_map.rs

@@ -1,6 +1,6 @@
 use crate::fmt;
 use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable};
-use crate::ops::{ControlFlow, Try};
+use crate::ops::{ControlFlow, TryWhereOutputEquals};
 
 /// An iterator that uses `f` to both filter and map elements from `iter`.
 ///
@@ -39,7 +39,7 @@ fn filter_map_fold<T, B, Acc>(
     }
 }
 
-fn filter_map_try_fold<'a, T, B, Acc, R: Try<Ok = Acc>>(
+fn filter_map_try_fold<'a, T, B, Acc, R: TryWhereOutputEquals<Acc>>(
     f: &'a mut impl FnMut(T) -> Option<B>,
     mut fold: impl FnMut(Acc, B) -> R + 'a,
 ) -> impl FnMut(Acc, T) -> R + 'a {
@@ -72,7 +72,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.iter.try_fold(init, filter_map_try_fold(&mut self.f, fold))
     }
@@ -111,7 +111,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.iter.try_rfold(init, filter_map_try_fold(&mut self.f, fold))
     }

library/core/src/iter/adapters/flatten.rs

@@ -1,6 +1,6 @@
 use crate::fmt;
 use crate::iter::{DoubleEndedIterator, Fuse, FusedIterator, Iterator, Map};
-use crate::ops::Try;
+use crate::ops::TryWhereOutputEquals;
 
 /// An iterator that maps each element to an iterator, and yields the elements
 /// of the produced iterators.
@@ -61,7 +61,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.inner.try_fold(init, fold)
     }
@@ -91,7 +91,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.inner.try_rfold(init, fold)
     }
@@ -178,7 +178,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.inner.try_fold(init, fold)
     }
@@ -208,7 +208,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         self.inner.try_rfold(init, fold)
     }
@@ -293,10 +293,10 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         #[inline]
-        fn flatten<'a, T: IntoIterator, Acc, R: Try<Ok = Acc>>(
+        fn flatten<'a, T: IntoIterator, Acc, R: TryWhereOutputEquals<Acc>>(
             frontiter: &'a mut Option<T::IntoIter>,
             fold: &'a mut impl FnMut(Acc, T::Item) -> R,
         ) -> impl FnMut(Acc, T) -> R + 'a {
@@ -382,10 +382,10 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: TryWhereOutputEquals<Acc>,
     {
         #[inline]
-        fn flatten<'a, T: IntoIterator, Acc, R: Try<Ok = Acc>>(
+        fn flatten<'a, T: IntoIterator, Acc, R: TryWhereOutputEquals<Acc>>(
             backiter: &'a mut Option<T::IntoIter>,
             fold: &'a mut impl FnMut(Acc, T::Item) -> R,
         ) -> impl FnMut(Acc, T) -> R + 'a