rust: upgrade to Rust 1.71.1

This is the second upgrade to the Rust toolchain, from 1.68.2 to 1.71.1
(i.e. the latest).

See the upgrade policy [1] and the comments on the first upgrade in
commit 3ed03f4da06e ("rust: upgrade to Rust 1.68.2").

# Unstable features

No unstable features (that we use) were stabilized.

Therefore, the only unstable feature allowed to be used outside
the `kernel` crate is still `new_uninit`, though other code to be
upstreamed may increase the list.

Please see [2] for details.

# Required changes

For the upgrade, this patch requires the following changes:

  - Removal of the `__rust_*` allocator functions, together with
    the addition of the `__rust_no_alloc_shim_is_unstable` static.
    See [3] for details.

  - Some more compiler builtins added due to `<f{32,64}>::midpoint()`
    that got added in Rust 1.71 [4].

# `alloc` upgrade and reviewing

The vast majority of changes are due to our `alloc` fork being upgraded
at once.

There are two kinds of changes to be aware of: the ones coming from
upstream, which we should follow as closely as possible, and the updates
needed in our added fallible APIs to keep them matching the newer
infallible APIs coming from upstream.

Instead of taking a look at the diff of this patch, an alternative
approach is reviewing a diff of the changes between upstream `alloc` and
the kernel's. This allows to easily inspect the kernel additions only,
especially to check if the fallible methods we already have still match
the infallible ones in the new version coming from upstream.

Another approach is reviewing the changes introduced in the additions in
the kernel fork between the two versions. This is useful to spot
potentially unintended changes to our additions.

To apply these approaches, one may follow steps similar to the following
to generate a pair of patches that show the differences between upstream
Rust and the kernel (for the subset of `alloc` we use) before and after
applying this patch:

    # Get the difference with respect to the old version.
    git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
    git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
        cut -d/ -f3- |
        grep -Fv README.md |
        xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
    git -C linux diff --patch-with-stat --summary -R > old.patch
    git -C linux restore rust/alloc

    # Apply this patch.
    git -C linux am rust-upgrade.patch

    # Get the difference with respect to the new version.
    git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
    git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
        cut -d/ -f3- |
        grep -Fv README.md |
        xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
    git -C linux diff --patch-with-stat --summary -R > new.patch
    git -C linux restore rust/alloc

Now one may check the `new.patch` to take a look at the additions (first
approach) or at the difference between those two patches (second
approach). For the latter, a side-by-side tool is recommended.

Link: https://rust-for-linux.com/rust-version-policy [1]
Link: https://github.com/Rust-for-Linux/linux/issues/2 [2]
Link: https://github.com/rust-lang/rust/pull/86844 [3]
Link: https://github.com/rust-lang/rust/pull/92048 [4]
Closes: https://github.com/Rust-for-Linux/linux/issues/68
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Link: https://lore.kernel.org/r/20230729220317.416771-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

4 files changed, 49 insertions, 86 deletions

diff --git a/rust/alloc/vec/drain.rs b/rust/alloc/vec/drain.rs
index d503d2f478ce..78177a9e2ad0 100644
--- a/rust/alloc/vec/drain.rs
+++ b/rust/alloc/vec/drain.rs
@@ -18,7 +18,7 @@ use super::Vec;
 ///
 /// ```
 /// let mut v = vec![0, 1, 2];
-/// let iter: std::vec::Drain<_> = v.drain(..);
+/// let iter: std::vec::Drain<'_, _> = v.drain(..);
 /// ```
 #[stable(feature = "drain", since = "1.6.0")]
 pub struct Drain<
@@ -114,9 +114,7 @@ impl<'a, T, A: Allocator> Drain<'a, T, A> {
             let unyielded_ptr = this.iter.as_slice().as_ptr();
 
             // ZSTs have no identity, so we don't need to move them around.
-            let needs_move = mem::size_of::<T>() != 0;
-
-            if needs_move {
+            if !T::IS_ZST {
                 let start_ptr = source_vec.as_mut_ptr().add(start);
 
                 // memmove back unyielded elements
@@ -199,7 +197,7 @@ impl<T, A: Allocator> Drop for Drain<'_, T, A> {
             }
         }
 
-        let iter = mem::replace(&mut self.iter, (&mut []).iter());
+        let iter = mem::take(&mut self.iter);
         let drop_len = iter.len();
 
         let mut vec = self.vec;
diff --git a/rust/alloc/vec/drain_filter.rs b/rust/alloc/vec/drain_filter.rs
index 4b019220657d..09efff090e42 100644
--- a/rust/alloc/vec/drain_filter.rs
+++ b/rust/alloc/vec/drain_filter.rs
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
 use crate::alloc::{Allocator, Global};
-use core::mem::{self, ManuallyDrop};
+use core::mem::{ManuallyDrop, SizedTypeProperties};
 use core::ptr;
 use core::slice;
 
@@ -18,7 +18,7 @@ use super::Vec;
 /// #![feature(drain_filter)]
 ///
 /// let mut v = vec![0, 1, 2];
-/// let iter: std::vec::DrainFilter<_, _> = v.drain_filter(|x| *x % 2 == 0);
+/// let iter: std::vec::DrainFilter<'_, _, _> = v.drain_filter(|x| *x % 2 == 0);
 /// ```
 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
 #[derive(Debug)]
@@ -98,9 +98,7 @@ where
 
         unsafe {
             // ZSTs have no identity, so we don't need to move them around.
-            let needs_move = mem::size_of::<T>() != 0;
-
-            if needs_move && this.idx < this.old_len && this.del > 0 {
+            if !T::IS_ZST && this.idx < this.old_len && this.del > 0 {
                 let ptr = this.vec.as_mut_ptr();
                 let src = ptr.add(this.idx);
                 let dst = src.sub(this.del);
diff --git a/rust/alloc/vec/into_iter.rs b/rust/alloc/vec/into_iter.rs
index 34a2a70d6ded..aac0ec16aef1 100644
--- a/rust/alloc/vec/into_iter.rs
+++ b/rust/alloc/vec/into_iter.rs
@@ -13,6 +13,7 @@ use core::iter::{
 };
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
+use core::num::NonZeroUsize;
 #[cfg(not(no_global_oom_handling))]
 use core::ops::Deref;
 use core::ptr::{self, NonNull};
@@ -109,7 +110,7 @@ impl<T, A: Allocator> IntoIter<T, A> {
     /// ```
     /// # let mut into_iter = Vec::<u8>::with_capacity(10).into_iter();
     /// let mut into_iter = std::mem::replace(&mut into_iter, Vec::new().into_iter());
-    /// (&mut into_iter).for_each(core::mem::drop);
+    /// (&mut into_iter).for_each(drop);
     /// std::mem::forget(into_iter);
     /// ```
     ///
@@ -215,7 +216,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
     }
 
     #[inline]
-    fn advance_by(&mut self, n: usize) -> Result<(), usize> {
+    fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
         let step_size = self.len().min(n);
         let to_drop = ptr::slice_from_raw_parts_mut(self.ptr as *mut T, step_size);
         if T::IS_ZST {
@@ -229,10 +230,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         unsafe {
             ptr::drop_in_place(to_drop);
         }
-        if step_size < n {
-            return Err(step_size);
-        }
-        Ok(())
+        NonZeroUsize::new(n - step_size).map_or(Ok(()), Err)
     }
 
     #[inline]
@@ -315,7 +313,7 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
     }
 
     #[inline]
-    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
         let step_size = self.len().min(n);
         if T::IS_ZST {
             // SAFETY: same as for advance_by()
@@ -329,10 +327,7 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
         unsafe {
             ptr::drop_in_place(to_drop);
         }
-        if step_size < n {
-            return Err(step_size);
-        }
-        Ok(())
+        NonZeroUsize::new(n - step_size).map_or(Ok(()), Err)
     }
 }
 
@@ -349,6 +344,24 @@ impl<T, A: Allocator> FusedIterator for IntoIter<T, A> {}
 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<T, A: Allocator> TrustedLen for IntoIter<T, A> {}
 
+#[stable(feature = "default_iters", since = "1.70.0")]
+impl<T, A> Default for IntoIter<T, A>
+where
+    A: Allocator + Default,
+{
+    /// Creates an empty `vec::IntoIter`.
+    ///
+    /// ```
+    /// # use std::vec;
+    /// let iter: vec::IntoIter<u8> = Default::default();
+    /// assert_eq!(iter.len(), 0);
+    /// assert_eq!(iter.as_slice(), &[]);
+    /// ```
+    fn default() -> Self {
+        super::Vec::new_in(Default::default()).into_iter()
+    }
+}
+
 #[doc(hidden)]
 #[unstable(issue = "none", feature = "std_internals")]
 #[rustc_unsafe_specialization_marker]
diff --git a/rust/alloc/vec/mod.rs b/rust/alloc/vec/mod.rs
index 94995913566b..05c70de0227e 100644
--- a/rust/alloc/vec/mod.rs
+++ b/rust/alloc/vec/mod.rs
@@ -58,13 +58,9 @@
 #[cfg(not(no_global_oom_handling))]
 use core::cmp;
 use core::cmp::Ordering;
-use core::convert::TryFrom;
 use core::fmt;
 use core::hash::{Hash, Hasher};
-use core::intrinsics::assume;
 use core::iter;
-#[cfg(not(no_global_oom_handling))]
-use core::iter::FromIterator;
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
@@ -381,8 +377,8 @@ mod spec_extend;
 /// Currently, `Vec` does not guarantee the order in which elements are dropped.
 /// The order has changed in the past and may change again.
 ///
-/// [`get`]: ../../std/vec/struct.Vec.html#method.get
-/// [`get_mut`]: ../../std/vec/struct.Vec.html#method.get_mut
+/// [`get`]: slice::get
+/// [`get_mut`]: slice::get_mut
 /// [`String`]: crate::string::String
 /// [`&str`]: type@str
 /// [`shrink_to_fit`]: Vec::shrink_to_fit
@@ -708,14 +704,14 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// // The vector contains no items, even though it has capacity for more
     /// assert_eq!(vec.len(), 0);
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     ///
     /// // These are all done without reallocating...
     /// for i in 0..10 {
     ///     vec.push(i);
     /// }
     /// assert_eq!(vec.len(), 10);
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     ///
     /// // ...but this may make the vector reallocate
     /// vec.push(11);
@@ -766,14 +762,14 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// // The vector contains no items, even though it has capacity for more
     /// assert_eq!(vec.len(), 0);
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     ///
     /// // These are all done without reallocating...
     /// for i in 0..10 {
     ///     vec.push(i);
     /// }
     /// assert_eq!(vec.len(), 10);
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     ///
     /// // ...but this may make the vector reallocate
     /// vec.push(11);
@@ -999,7 +995,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     /// let mut vec: Vec<i32> = Vec::with_capacity(10);
     /// vec.push(42);
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -1150,7 +1146,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     /// let mut vec = Vec::with_capacity(10);
     /// vec.extend([1, 2, 3]);
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     /// vec.shrink_to_fit();
     /// assert!(vec.capacity() >= 3);
     /// ```
@@ -1177,7 +1173,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// ```
     /// let mut vec = Vec::with_capacity(10);
     /// vec.extend([1, 2, 3]);
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     /// vec.shrink_to(4);
     /// assert!(vec.capacity() >= 4);
     /// vec.shrink_to(0);
@@ -1212,7 +1208,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// let mut vec = Vec::with_capacity(10);
     /// vec.extend([1, 2, 3]);
     ///
-    /// assert_eq!(vec.capacity(), 10);
+    /// assert!(vec.capacity() >= 10);
     /// let slice = vec.into_boxed_slice();
     /// assert_eq!(slice.into_vec().capacity(), 3);
     /// ```
@@ -1358,11 +1354,7 @@ impl<T, A: Allocator> Vec<T, A> {
     pub fn as_ptr(&self) -> *const T {
         // We shadow the slice method of the same name to avoid going through
         // `deref`, which creates an intermediate reference.
-        let ptr = self.buf.ptr();
-        unsafe {
-            assume(!ptr.is_null());
-        }
-        ptr
+        self.buf.ptr()
     }
 
     /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
@@ -1395,11 +1387,7 @@ impl<T, A: Allocator> Vec<T, A> {
     pub fn as_mut_ptr(&mut self) -> *mut T {
         // We shadow the slice method of the same name to avoid going through
         // `deref_mut`, which creates an intermediate reference.
-        let ptr = self.buf.ptr();
-        unsafe {
-            assume(!ptr.is_null());
-        }
-        ptr
+        self.buf.ptr()
     }
 
     /// Returns a reference to the underlying allocator.
@@ -2892,35 +2880,6 @@ impl<T, A: Allocator> ops::DerefMut for Vec<T, A> {
 }
 
 #[cfg(not(no_global_oom_handling))]
-trait SpecCloneFrom {
-    fn clone_from(this: &mut Self, other: &Self);
-}
-
-#[cfg(not(no_global_oom_handling))]
-impl<T: Clone, A: Allocator> SpecCloneFrom for Vec<T, A> {
-    default fn clone_from(this: &mut Self, other: &Self) {
-        // drop anything that will not be overwritten
-        this.truncate(other.len());
-
-        // self.len <= other.len due to the truncate above, so the
-        // slices here are always in-bounds.
-        let (init, tail) = other.split_at(this.len());
-
-        // reuse the contained values' allocations/resources.
-        this.clone_from_slice(init);
-        this.extend_from_slice(tail);
-    }
-}
-
-#[cfg(not(no_global_oom_handling))]
-impl<T: Copy, A: Allocator> SpecCloneFrom for Vec<T, A> {
-    fn clone_from(this: &mut Self, other: &Self) {
-        this.clear();
-        this.extend_from_slice(other);
-    }
-}
-
-#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
     #[cfg(not(test))]
@@ -2940,7 +2899,7 @@ impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
     }
 
     fn clone_from(&mut self, other: &Self) {
-        SpecCloneFrom::clone_from(self, other)
+        crate::slice::SpecCloneIntoVec::clone_into(other.as_slice(), self);
     }
 }
 
@@ -2948,7 +2907,6 @@ impl<T: Clone, A: Allocator + Clone> Clone for Vec<T, A> {
 /// as required by the `core::borrow::Borrow` implementation.
 ///
 /// ```
-/// #![feature(build_hasher_simple_hash_one)]
 /// use std::hash::BuildHasher;
 ///
 /// let b = std::collections::hash_map::RandomState::new();
@@ -3330,7 +3288,7 @@ impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
     }
 }
 
-/// Implements comparison of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
+/// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
     #[inline]
@@ -3342,7 +3300,7 @@ impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Eq, A: Allocator> Eq for Vec<T, A> {}
 
-/// Implements ordering of vectors, [lexicographically](core::cmp::Ord#lexicographical-comparison).
+/// Implements ordering of vectors, [lexicographically](Ord#lexicographical-comparison).
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord, A: Allocator> Ord for Vec<T, A> {
     #[inline]
@@ -3365,8 +3323,7 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
-impl<T> const Default for Vec<T> {
+impl<T> Default for Vec<T> {
     /// Creates an empty `Vec<T>`.
     ///
     /// The vector will not allocate until elements are pushed onto it.
@@ -3462,10 +3419,7 @@ impl<T, const N: usize> From<[T; N]> for Vec<T> {
     /// ```
     #[cfg(not(test))]
     fn from(s: [T; N]) -> Vec<T> {
-        <[T]>::into_vec(
-            #[rustc_box]
-            Box::new(s),
-        )
+        <[T]>::into_vec(Box::new(s))
     }
 
     #[cfg(test)]
@@ -3490,8 +3444,8 @@ where
     ///
     /// ```
     /// # use std::borrow::Cow;
-    /// let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]);
-    /// let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]);
+    /// let o: Cow<'_, [i32]> = Cow::Owned(vec![1, 2, 3]);
+    /// let b: Cow<'_, [i32]> = Cow::Borrowed(&[1, 2, 3]);
     /// assert_eq!(Vec::from(o), Vec::from(b));
     /// ```
     fn from(s: Cow<'a, [T]>) -> Vec<T> {