Auto merge of #27808 - SimonSapin:utf16decoder, r=alexcrichton

* Rename `Utf16Items` to `Utf16Decoder`. "Items" is meaningless.
* Generalize it to any `u16` iterator, not just `[u16].iter()`
* Make it yield `Result` instead of a custom `Utf16Item` enum that was isomorphic to `Result`. This enable using the `FromIterator for Result` impl.
* Replace `Utf16Item::to_char_lossy` with a `Utf16Decoder::lossy` iterator adaptor.

This is a [breaking change], but only for users of the unstable `rustc_unicode` crate.

I’d like this functionality to be stabilized and re-exported in `std` eventually, as the "low-level equivalent" of `String::from_utf16` and `String::from_utf16_lossy` like #27784 is the low-level equivalent of #27714.

CC @aturon, @alexcrichton 

3 files changed, 18 insertions, 0 deletions

diff --git a/src/liballoc/arc.rs b/src/liballoc/arc.rs
index bb2daa2a1d7..b68d7976540 100644
--- a/src/liballoc/arc.rs
+++ b/src/liballoc/arc.rs
@@ -73,6 +73,7 @@ use boxed::Box;
 
 use core::sync::atomic;
 use core::sync::atomic::Ordering::{Relaxed, Release, Acquire, SeqCst};
+use core::borrow;
 use core::fmt;
 use core::cmp::Ordering;
 use core::mem::{align_of_val, size_of_val};
@@ -1109,3 +1110,7 @@ mod tests {
         assert!(y.upgrade().is_none());
     }
 }
+
+impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
+    fn borrow(&self) -> &T { &**self }
+}
diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index e3019f952fe..a6e0f3a9bd9 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -57,6 +57,7 @@ use heap;
 use raw_vec::RawVec;
 
 use core::any::Any;
+use core::borrow;
 use core::cmp::Ordering;
 use core::fmt;
 use core::hash::{self, Hash};
@@ -562,3 +563,10 @@ impl<T: Clone> Clone for Box<[T]> {
     }
 }
 
+impl<T: ?Sized> borrow::Borrow<T> for Box<T> {
+    fn borrow(&self) -> &T { &**self }
+}
+
+impl<T: ?Sized> borrow::BorrowMut<T> for Box<T> {
+    fn borrow_mut(&mut self) -> &mut T { &mut **self }
+}
diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index 9649d0f71a1..b1fb5be4d21 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -158,6 +158,7 @@ use boxed::Box;
 #[cfg(test)]
 use std::boxed::Box;
 
+use core::borrow;
 use core::cell::Cell;
 use core::cmp::Ordering;
 use core::fmt;
@@ -1091,3 +1092,7 @@ mod tests {
         assert_eq!(foo, foo.clone());
     }
 }
+
+impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
+    fn borrow(&self) -> &T { &**self }
+}