Auto merge of rust-lang#77381 - Dylan-DPC:rollup-0sr6p5p, r=Dylan-DPC

Rollup of 12 pull requests

Successful merges:

 - rust-lang#76909 (Add Iterator::advance_by and DoubleEndedIterator::advance_back_by)
 - rust-lang#77153 (Fix recursive nonterminal expansion during pretty-print/reparse check)
 - rust-lang#77202 (Defer Apple SDKROOT detection to link time.)
 - rust-lang#77303 (const evaluatable: improve `TooGeneric` handling)
 - rust-lang#77305 (move candidate_from_obligation_no_cache)
 - rust-lang#77315 (Rename AllocErr to AllocError)
 - rust-lang#77319 (Stable hashing: add comments and tests concerning platform-independence)
 - rust-lang#77324 (Don't fire `const_item_mutation` lint on writes through a pointer)
 - rust-lang#77343 (Validate `rustc_args_required_const`)
 - rust-lang#77349 (Update cargo)
 - rust-lang#77360 (References to ZSTs may be at arbitrary aligned addresses)
 - rust-lang#77371 (Remove trailing space in error message)

Failed merges:

r? `@ghost`

Author: bors

alloc/src/alloc.rs

@@ -145,13 +145,13 @@ pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
 
 impl Global {
     #[inline]
-    fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc_impl(&self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocError> {
         match layout.size() {
             0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
             // SAFETY: `layout` is non-zero in size,
             size => unsafe {
                 let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
-                let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
                 Ok(NonNull::slice_from_raw_parts(ptr, size))
             },
         }
@@ -165,7 +165,7 @@ impl Global {
         old_layout: Layout,
         new_layout: Layout,
         zeroed: bool,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         debug_assert!(
             new_layout.size() >= old_layout.size(),
             "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
@@ -183,7 +183,7 @@ impl Global {
                 intrinsics::assume(new_size >= old_layout.size());
 
                 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
-                let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
                 if zeroed {
                     raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
                 }
@@ -208,12 +208,12 @@ impl Global {
 #[unstable(feature = "allocator_api", issue = "32838")]
 unsafe impl AllocRef for Global {
     #[inline]
-    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         self.alloc_impl(layout, false)
     }
 
     #[inline]
-    fn alloc_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         self.alloc_impl(layout, true)
     }
 
@@ -232,7 +232,7 @@ unsafe impl AllocRef for Global {
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         // SAFETY: all conditions must be upheld by the caller
         unsafe { self.grow_impl(ptr, old_layout, new_layout, false) }
     }
@@ -243,7 +243,7 @@ unsafe impl AllocRef for Global {
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         // SAFETY: all conditions must be upheld by the caller
         unsafe { self.grow_impl(ptr, old_layout, new_layout, true) }
     }
@@ -254,7 +254,7 @@ unsafe impl AllocRef for Global {
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         debug_assert!(
             new_layout.size() <= old_layout.size(),
             "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
@@ -273,7 +273,7 @@ unsafe impl AllocRef for Global {
                 intrinsics::assume(new_size <= old_layout.size());
 
                 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
-                let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocError)?;
                 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
             },
 

alloc/src/raw_vec/tests.rs

@@ -3,7 +3,7 @@ use std::cell::Cell;
 
 #[test]
 fn allocator_param() {
-    use crate::alloc::AllocErr;
+    use crate::alloc::AllocError;
 
     // Writing a test of integration between third-party
     // allocators and `RawVec` is a little tricky because the `RawVec`
@@ -21,10 +21,10 @@ fn allocator_param() {
         fuel: Cell<usize>,
     }
     unsafe impl AllocRef for BoundedAlloc {
-        fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+        fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
             let size = layout.size();
             if size > self.fuel.get() {
-                return Err(AllocErr);
+                return Err(AllocError);
             }
             match Global.alloc(layout) {
                 ok @ Ok(_) => {

alloc/src/rc.rs

@@ -247,7 +247,7 @@ use core::pin::Pin;
 use core::ptr::{self, NonNull};
 use core::slice::from_raw_parts_mut;
 
-use crate::alloc::{box_free, handle_alloc_error, AllocErr, AllocRef, Global, Layout};
+use crate::alloc::{box_free, handle_alloc_error, AllocError, AllocRef, Global, Layout};
 use crate::borrow::{Cow, ToOwned};
 use crate::string::String;
 use crate::vec::Vec;
@@ -996,7 +996,7 @@ impl<T: ?Sized> Rc<T> {
     /// and must return back a (potentially fat)-pointer for the `RcBox<T>`.
     unsafe fn allocate_for_layout(
         value_layout: Layout,
-        allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocErr>,
+        allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocError>,
         mem_to_rcbox: impl FnOnce(*mut u8) -> *mut RcBox<T>,
     ) -> *mut RcBox<T> {
         // Calculate layout using the given value layout.

alloc/src/sync.rs

@@ -21,7 +21,7 @@ use core::slice::from_raw_parts_mut;
 use core::sync::atomic;
 use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
 
-use crate::alloc::{box_free, handle_alloc_error, AllocErr, AllocRef, Global, Layout};
+use crate::alloc::{box_free, handle_alloc_error, AllocError, AllocRef, Global, Layout};
 use crate::borrow::{Cow, ToOwned};
 use crate::boxed::Box;
 use crate::rc::is_dangling;
@@ -969,7 +969,7 @@ impl<T: ?Sized> Arc<T> {
     /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`.
     unsafe fn allocate_for_layout(
         value_layout: Layout,
-        allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocErr>,
+        allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocError>,
         mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>,
     ) -> *mut ArcInner<T> {
         // Calculate layout using the given value layout.

core/src/alloc/mod.rs

@@ -13,17 +13,17 @@ pub use self::layout::{Layout, LayoutErr};
 use crate::fmt;
 use crate::ptr::{self, NonNull};
 
-/// The `AllocErr` error indicates an allocation failure
+/// The `AllocError` error indicates an allocation failure
 /// that may be due to resource exhaustion or to
 /// something wrong when combining the given input arguments with this
 /// allocator.
 #[unstable(feature = "allocator_api", issue = "32838")]
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
-pub struct AllocErr;
+pub struct AllocError;
 
 // (we need this for downstream impl of trait Error)
 #[unstable(feature = "allocator_api", issue = "32838")]
-impl fmt::Display for AllocErr {
+impl fmt::Display for AllocError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str("memory allocation failed")
     }
@@ -109,7 +109,7 @@ pub unsafe trait AllocRef {
     /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
     ///
     /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr>;
+    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>;
 
     /// Behaves like `alloc`, but also ensures that the returned memory is zero-initialized.
     ///
@@ -126,7 +126,7 @@ pub unsafe trait AllocRef {
     /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
     ///
     /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
-    fn alloc_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         let ptr = self.alloc(layout)?;
         // SAFETY: `alloc` returns a valid memory block
         unsafe { ptr.as_non_null_ptr().as_ptr().write_bytes(0, ptr.len()) }
@@ -187,7 +187,7 @@ pub unsafe trait AllocRef {
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         debug_assert!(
             new_layout.size() >= old_layout.size(),
             "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
@@ -248,7 +248,7 @@ pub unsafe trait AllocRef {
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         debug_assert!(
             new_layout.size() >= old_layout.size(),
             "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
@@ -312,7 +312,7 @@ pub unsafe trait AllocRef {
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         debug_assert!(
             new_layout.size() <= old_layout.size(),
             "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
@@ -348,12 +348,12 @@ where
     A: AllocRef + ?Sized,
 {
     #[inline]
-    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         (**self).alloc(layout)
     }
 
     #[inline]
-    fn alloc_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+    fn alloc_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
         (**self).alloc_zeroed(layout)
     }
 
@@ -369,7 +369,7 @@ where
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         // SAFETY: the safety contract must be upheld by the caller
         unsafe { (**self).grow(ptr, old_layout, new_layout) }
     }
@@ -380,7 +380,7 @@ where
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         // SAFETY: the safety contract must be upheld by the caller
         unsafe { (**self).grow_zeroed(ptr, old_layout, new_layout) }
     }
@@ -391,7 +391,7 @@ where
         ptr: NonNull<u8>,
         old_layout: Layout,
         new_layout: Layout,
-    ) -> Result<NonNull<[u8]>, AllocErr> {
+    ) -> Result<NonNull<[u8]>, AllocError> {
         // SAFETY: the safety contract must be upheld by the caller
         unsafe { (**self).shrink(ptr, old_layout, new_layout) }
     }

core/src/iter/adapters/mod.rs

@@ -124,6 +124,11 @@ where
         self.iter.size_hint()
     }
 
+    #[inline]
+    fn advance_by(&mut self, n: usize) -> Result<(), usize> {
+        self.iter.advance_back_by(n)
+    }
+
     #[inline]
     fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
         self.iter.nth_back(n)
@@ -164,6 +169,11 @@ where
         self.iter.next()
     }
 
+    #[inline]
+    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+        self.iter.advance_by(n)
+    }
+
     #[inline]
     fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
         self.iter.nth(n)

core/src/iter/traits/double_ended.rs

@@ -91,6 +91,46 @@ pub trait DoubleEndedIterator: Iterator {
     #[stable(feature = "rust1", since = "1.0.0")]
     fn next_back(&mut self) -> Option<Self::Item>;
 
+    /// Advances the iterator from the back by `n` elements.
+    ///
+    /// `advance_back_by` is the reverse version of [`advance_by`]. This method will
+    /// eagerly skip `n` elements starting from the back by calling [`next_back`] up
+    /// to `n` times until [`None`] is encountered.
+    ///
+    /// `advance_back_by(n)` will return [`Ok(())`] if the iterator successfully advances by
+    /// `n` elements, or [`Err(k)`] if [`None`] is encountered, where `k` is the number of
+    /// elements the iterator is advanced by before running out of elements (i.e. the length
+    /// of the iterator). Note that `k` is always less than `n`.
+    ///
+    /// Calling `advance_back_by(0)` does not consume any elements and always returns [`Ok(())`].
+    ///
+    /// [`advance_by`]: Iterator::advance_by
+    /// [`next_back`]: DoubleEndedIterator::next_back
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(iter_advance_by)]
+    ///
+    /// let a = [3, 4, 5, 6];
+    /// let mut iter = a.iter();
+    ///
+    /// assert_eq!(iter.advance_back_by(2), Ok(()));
+    /// assert_eq!(iter.next_back(), Some(&4));
+    /// assert_eq!(iter.advance_back_by(0), Ok(()));
+    /// assert_eq!(iter.advance_back_by(100), Err(1)); // only `&3` was skipped
+    /// ```
+    #[inline]
+    #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "none")]
+    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+        for i in 0..n {
+            self.next_back().ok_or(i)?;
+        }
+        Ok(())
+    }
+
     /// Returns the `n`th element from the end of the iterator.
     ///
     /// This is essentially the reversed version of [`Iterator::nth()`].
@@ -134,14 +174,9 @@ pub trait DoubleEndedIterator: Iterator {
     /// ```
     #[inline]
     #[stable(feature = "iter_nth_back", since = "1.37.0")]
-    fn nth_back(&mut self, mut n: usize) -> Option<Self::Item> {
-        for x in self.rev() {
-            if n == 0 {
-                return Some(x);
-            }
-            n -= 1;
-        }
-        None
+    fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
+        self.advance_back_by(n).ok()?;
+        self.next_back()
     }
 
     /// This is the reverse version of [`Iterator::try_fold()`]: it takes
@@ -318,6 +353,9 @@ impl<'a, I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for &'a mut I {
     fn next_back(&mut self) -> Option<I::Item> {
         (**self).next_back()
     }
+    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+        (**self).advance_back_by(n)
+    }
     fn nth_back(&mut self, n: usize) -> Option<I::Item> {
         (**self).nth_back(n)
     }