Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2023 insertions, 0 deletions

diff --git a/third_party/rust/bumpalo/src/lib.rs b/third_party/rust/bumpalo/src/lib.rs
new file mode 100644
index 0000000000..74dfcd4361
--- /dev/null
+++ b/third_party/rust/bumpalo/src/lib.rs
@@ -0,0 +1,2023 @@
+#![doc = include_str!("../README.md")]
+#![deny(missing_debug_implementations)]
+#![deny(missing_docs)]
+#![no_std]
+#![cfg_attr(
+    feature = "allocator_api",
+    feature(allocator_api, nonnull_slice_from_raw_parts)
+)]
+
+#[doc(hidden)]
+pub extern crate alloc as core_alloc;
+
+#[cfg(feature = "boxed")]
+pub mod boxed;
+#[cfg(feature = "collections")]
+pub mod collections;
+
+mod alloc;
+
+use core::cell::Cell;
+use core::fmt::Display;
+use core::iter;
+use core::marker::PhantomData;
+use core::mem;
+use core::ptr::{self, NonNull};
+use core::slice;
+use core::str;
+use core_alloc::alloc::{alloc, dealloc, Layout};
+#[cfg(feature = "allocator_api")]
+use core_alloc::alloc::{AllocError, Allocator};
+
+pub use alloc::AllocErr;
+
+/// An error returned from [`Bump::try_alloc_try_with`].
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum AllocOrInitError<E> {
+    /// Indicates that the initial allocation failed.
+    Alloc(AllocErr),
+    /// Indicates that the initializer failed with the contained error after
+    /// allocation.
+    ///
+    /// It is possible but not guaranteed that the allocated memory has been
+    /// released back to the allocator at this point.
+    Init(E),
+}
+impl<E> From<AllocErr> for AllocOrInitError<E> {
+    fn from(e: AllocErr) -> Self {
+        Self::Alloc(e)
+    }
+}
+impl<E: Display> Display for AllocOrInitError<E> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            AllocOrInitError::Alloc(err) => err.fmt(f),
+            AllocOrInitError::Init(err) => write!(f, "initialization failed: {}", err),
+        }
+    }
+}
+
+/// An arena to bump allocate into.
+///
+/// ## No `Drop`s
+///
+/// Objects that are bump-allocated will never have their [`Drop`] implementation
+/// called &mdash; unless you do it manually yourself. This makes it relatively
+/// easy to leak memory or other resources.
+///
+/// If you have a type which internally manages
+///
+/// * an allocation from the global heap (e.g. [`Vec<T>`]),
+/// * open file descriptors (e.g. [`std::fs::File`]), or
+/// * any other resource that must be cleaned up (e.g. an `mmap`)
+///
+/// and relies on its `Drop` implementation to clean up the internal resource,
+/// then if you allocate that type with a `Bump`, you need to find a new way to
+/// clean up after it yourself.
+///
+/// Potential solutions are:
+///
+/// * Using [`bumpalo::boxed::Box::new_in`] instead of [`Bump::alloc`], that
+///   will drop wrapped values similarly to [`std::boxed::Box`]. Note that this
+///   requires enabling the `"boxed"` Cargo feature for this crate. **This is
+///   often the easiest solution.**
+///
+/// * Calling [`drop_in_place`][drop_in_place] or using
+///   [`std::mem::ManuallyDrop`][manuallydrop] to manually drop these types.
+///
+/// * Using [`bumpalo::collections::Vec`] instead of [`std::vec::Vec`].
+///
+/// * Avoiding allocating these problematic types within a `Bump`.
+///
+/// Note that not calling `Drop` is memory safe! Destructors are never
+/// guaranteed to run in Rust, you can't rely on them for enforcing memory
+/// safety.
+///
+/// [`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html
+/// [`Vec<T>`]: https://doc.rust-lang.org/std/vec/struct.Vec.html
+/// [`std::fs::File`]: https://doc.rust-lang.org/std/fs/struct.File.html
+/// [drop_in_place]: https://doc.rust-lang.org/std/ptr/fn.drop_in_place.html
+/// [manuallydrop]: https://doc.rust-lang.org/std/mem/struct.ManuallyDrop.html
+/// [`bumpalo::collections::Vec`]: collections/vec/struct.Vec.html
+/// [`std::vec::Vec`]: https://doc.rust-lang.org/std/vec/struct.Vec.html
+/// [`bumpalo::boxed::Box::new_in`]: boxed/struct.Box.html#method.new_in
+/// [`std::boxed::Box`]: https://doc.rust-lang.org/std/boxed/struct.Box.html
+///
+/// ## Example
+///
+/// ```
+/// use bumpalo::Bump;
+///
+/// // Create a new bump arena.
+/// let bump = Bump::new();
+///
+/// // Allocate values into the arena.
+/// let forty_two = bump.alloc(42);
+/// assert_eq!(*forty_two, 42);
+///
+/// // Mutable references are returned from allocation.
+/// let mut s = bump.alloc("bumpalo");
+/// *s = "the bump allocator; and also is a buffalo";
+/// ```
+///
+/// ## Allocation Methods Come in Many Flavors
+///
+/// There are various allocation methods on `Bump`, the simplest being
+/// [`alloc`][Bump::alloc]. The others exist to satisfy some combination of
+/// fallible allocation and initialization. The allocation methods are
+/// summarized in the following table:
+///
+/// <table>
+///   <thead>
+///     <tr>
+///       <th></th>
+///       <th>Infallible Allocation</th>
+///       <th>Fallible Allocation</th>
+///     </tr>
+///   </thead>
+///     <tr>
+///       <th>By Value</th>
+///       <td><a href="#method.alloc"><code>alloc</code></a></td>
+///       <td><a href="#method.try_alloc"><code>try_alloc</code></a></td>
+///     </tr>
+///     <tr>
+///       <th>Infallible Initializer Function</th>
+///       <td><a href="#method.alloc_with"><code>alloc_with</code></a></td>
+///       <td><a href="#method.try_alloc_with"><code>try_alloc_with</code></a></td>
+///     </tr>
+///     <tr>
+///       <th>Fallible Initializer Function</th>
+///       <td><a href="#method.alloc_try_with"><code>alloc_try_with</code></a></td>
+///       <td><a href="#method.try_alloc_try_with"><code>try_alloc_try_with</code></a></td>
+///     </tr>
+///   <tbody>
+///   </tbody>
+/// </table>
+///
+/// ### Fallible Allocation: The `try_alloc_` Method Prefix
+///
+/// These allocation methods let you recover from out-of-memory (OOM)
+/// scenarioes, rather than raising a panic on OOM.
+///
+/// ```
+/// use bumpalo::Bump;
+///
+/// let bump = Bump::new();
+///
+/// match bump.try_alloc(MyStruct {
+///     // ...
+/// }) {
+///     Ok(my_struct) => {
+///         // Allocation succeeded.
+///     }
+///     Err(e) => {
+///         // Out of memory.
+///     }
+/// }
+///
+/// struct MyStruct {
+///     // ...
+/// }
+/// ```
+///
+/// ### Initializer Functions: The `_with` Method Suffix
+///
+/// Calling one of the generic `…alloc(x)` methods is essentially equivalent to
+/// the matching [`…alloc_with(|| x)`](?search=alloc_with). However if you use
+/// `…alloc_with`, then the closure will not be invoked until after allocating
+/// space for storing `x` on the heap.
+///
+/// This can be useful in certain edge-cases related to compiler optimizations.
+/// When evaluating for example `bump.alloc(x)`, semantically `x` is first put
+/// on the stack and then moved onto the heap. In some cases, the compiler is
+/// able to optimize this into constructing `x` directly on the heap, however
+/// in many cases it does not.
+///
+/// The `…alloc_with` functions try to help the compiler be smarter. In most
+/// cases doing for example `bump.try_alloc_with(|| x)` on release mode will be
+/// enough to help the compiler realize that this optimization is valid and
+/// to construct `x` directly onto the heap.
+///
+/// #### Warning
+///
+/// These functions critically depend on compiler optimizations to achieve their
+/// desired effect. This means that it is not an effective tool when compiling
+/// without optimizations on.
+///
+/// Even when optimizations are on, these functions do not **guarantee** that
+/// the value is constructed on the heap. To the best of our knowledge no such
+/// guarantee can be made in stable Rust as of 1.54.
+///
+/// ### Fallible Initialization: The `_try_with` Method Suffix
+///
+/// The generic [`…alloc_try_with(|| x)`](?search=_try_with) methods behave
+/// like the purely `_with` suffixed methods explained above. However, they
+/// allow for fallible initialization by accepting a closure that returns a
+/// [`Result`] and will attempt to undo the initial allocation if this closure
+/// returns [`Err`].
+///
+/// #### Warning
+///
+/// If the inner closure returns [`Ok`], space for the entire [`Result`] remains
+/// allocated inside `self`. This can be a problem especially if the [`Err`]
+/// variant is larger, but even otherwise there may be overhead for the
+/// [`Result`]'s discriminant.
+///
+/// <p><details><summary>Undoing the allocation in the <code>Err</code> case
+/// always fails if <code>f</code> successfully made any additional allocations
+/// in <code>self</code>.</summary>
+///
+/// For example, the following will always leak also space for the [`Result`]
+/// into this `Bump`, even though the inner reference isn't kept and the [`Err`]
+/// payload is returned semantically by value:
+///
+/// ```rust
+/// let bump = bumpalo::Bump::new();
+///
+/// let r: Result<&mut [u8; 1000], ()> = bump.alloc_try_with(|| {
+///     let _ = bump.alloc(0_u8);
+///     Err(())
+/// });
+///
+/// assert!(r.is_err());
+/// ```
+///
+///</details></p>
+///
+/// Since [`Err`] payloads are first placed on the heap and then moved to the
+/// stack, `bump.…alloc_try_with(|| x)?` is likely to execute more slowly than
+/// the matching `bump.…alloc(x?)` in case of initialization failure. If this
+/// happens frequently, using the plain un-suffixed method may perform better.
+///
+/// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html
+/// [`Ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Ok
+/// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
+///
+/// ### `Bump` Allocation Limits
+///
+/// `bumpalo` supports setting a limit on the maximum bytes of memory that can
+/// be allocated for use in a particular `Bump` arena. This limit can be set and removed with
+/// [`set_allocation_limit`][Bump::set_allocation_limit].
+/// The allocation limit is only enforced when allocating new backing chunks for
+/// a `Bump`. Updating the allocation limit will not affect existing allocations
+/// or any future allocations within the `Bump`'s current chunk.
+///
+/// #### Example
+///
+/// ```
+/// let bump = bumpalo::Bump::new();
+///
+/// assert_eq!(bump.allocation_limit(), None);
+/// bump.set_allocation_limit(Some(0));
+///
+/// assert!(bump.try_alloc(5).is_err());
+///
+/// bump.set_allocation_limit(Some(6));
+///
+/// assert_eq!(bump.allocation_limit(), Some(6));
+///
+/// bump.set_allocation_limit(None);
+///
+/// assert_eq!(bump.allocation_limit(), None);
+/// ```
+///
+/// #### Warning
+///
+/// Because of backwards compatibility, allocations that fail
+/// due to allocation limits will not present differently than
+/// errors due to resource exhaustion.
+
+#[derive(Debug)]
+pub struct Bump {
+    // The current chunk we are bump allocating within.
+    current_chunk_footer: Cell<NonNull<ChunkFooter>>,
+    allocation_limit: Cell<Option<usize>>,
+}
+
+#[repr(C)]
+#[derive(Debug)]
+struct ChunkFooter {
+    // Pointer to the start of this chunk allocation. This footer is always at
+    // the end of the chunk.
+    data: NonNull<u8>,
+
+    // The layout of this chunk's allocation.
+    layout: Layout,
+
+    // Link to the previous chunk.
+    //
+    // Note that the last node in the `prev` linked list is the canonical empty
+    // chunk, whose `prev` link points to itself.
+    prev: Cell<NonNull<ChunkFooter>>,
+
+    // Bump allocation finger that is always in the range `self.data..=self`.
+    ptr: Cell<NonNull<u8>>,
+
+    // The bytes allocated in all chunks so far, the canonical empty chunk has
+    // a size of 0 and for all other chunks, `allocated_bytes` will be
+    // the allocated_bytes of the current chunk plus the allocated bytes
+    // of the `prev` chunk.
+    allocated_bytes: usize,
+}
+
+/// A wrapper type for the canonical, statically allocated empty chunk.
+///
+/// For the canonical empty chunk to be `static`, its type must be `Sync`, which
+/// is the purpose of this wrapper type. This is safe because the empty chunk is
+/// immutable and never actually modified.
+#[repr(transparent)]
+struct EmptyChunkFooter(ChunkFooter);
+
+unsafe impl Sync for EmptyChunkFooter {}
+
+static EMPTY_CHUNK: EmptyChunkFooter = EmptyChunkFooter(ChunkFooter {
+    // This chunk is empty (except the foot itself).
+    layout: Layout::new::<ChunkFooter>(),
+
+    // The start of the (empty) allocatable region for this chunk is itself.
+    data: unsafe { NonNull::new_unchecked(&EMPTY_CHUNK as *const EmptyChunkFooter as *mut u8) },
+
+    // The end of the (empty) allocatable region for this chunk is also itself.
+    ptr: Cell::new(unsafe {
+        NonNull::new_unchecked(&EMPTY_CHUNK as *const EmptyChunkFooter as *mut u8)
+    }),
+
+    // Invariant: the last chunk footer in all `ChunkFooter::prev` linked lists
+    // is the empty chunk footer, whose `prev` points to itself.
+    prev: Cell::new(unsafe {
+        NonNull::new_unchecked(&EMPTY_CHUNK as *const EmptyChunkFooter as *mut ChunkFooter)
+    }),
+
+    // Empty chunks count as 0 allocated bytes in an arena.
+    allocated_bytes: 0,
+});
+
+impl EmptyChunkFooter {
+    fn get(&'static self) -> NonNull<ChunkFooter> {
+        unsafe { NonNull::new_unchecked(&self.0 as *const ChunkFooter as *mut ChunkFooter) }
+    }
+}
+
+impl ChunkFooter {
+    // Returns the start and length of the currently allocated region of this
+    // chunk.
+    fn as_raw_parts(&self) -> (*const u8, usize) {
+        let data = self.data.as_ptr() as *const u8;
+        let ptr = self.ptr.get().as_ptr() as *const u8;
+        debug_assert!(data <= ptr);
+        debug_assert!(ptr <= self as *const ChunkFooter as *const u8);
+        let len = unsafe { (self as *const ChunkFooter as *const u8).offset_from(ptr) as usize };
+        (ptr, len)
+    }
+
+    /// Is this chunk the last empty chunk?
+    fn is_empty(&self) -> bool {
+        ptr::eq(self, EMPTY_CHUNK.get().as_ptr())
+    }
+}
+
+impl Default for Bump {
+    fn default() -> Bump {
+        Bump::new()
+    }
+}
+
+impl Drop for Bump {
+    fn drop(&mut self) {
+        unsafe {
+            dealloc_chunk_list(self.current_chunk_footer.get());
+        }
+    }
+}
+
+#[inline]
+unsafe fn dealloc_chunk_list(mut footer: NonNull<ChunkFooter>) {
+    while !footer.as_ref().is_empty() {
+        let f = footer;
+        footer = f.as_ref().prev.get();
+        dealloc(f.as_ref().data.as_ptr(), f.as_ref().layout);
+    }
+}
+
+// `Bump`s are safe to send between threads because nothing aliases its owned
+// chunks until you start allocating from it. But by the time you allocate from
+// it, the returned references to allocations borrow the `Bump` and therefore
+// prevent sending the `Bump` across threads until the borrows end.
+unsafe impl Send for Bump {}
+
+#[inline]
+pub(crate) fn round_up_to(n: usize, divisor: usize) -> Option<usize> {
+    debug_assert!(divisor > 0);
+    debug_assert!(divisor.is_power_of_two());
+    Some(n.checked_add(divisor - 1)? & !(divisor - 1))
+}
+
+#[inline]
+pub(crate) fn round_down_to(n: usize, divisor: usize) -> usize {
+    debug_assert!(divisor > 0);
+    debug_assert!(divisor.is_power_of_two());
+    n & !(divisor - 1)
+}
+
+// After this point, we try to hit page boundaries instead of powers of 2
+const PAGE_STRATEGY_CUTOFF: usize = 0x1000;
+
+// We only support alignments of up to 16 bytes for iter_allocated_chunks.
+const SUPPORTED_ITER_ALIGNMENT: usize = 16;
+const CHUNK_ALIGN: usize = SUPPORTED_ITER_ALIGNMENT;
+const FOOTER_SIZE: usize = mem::size_of::<ChunkFooter>();
+
+// Assert that ChunkFooter is at most the supported alignment. This will give a compile time error if it is not the case
+const _FOOTER_ALIGN_ASSERTION: bool = mem::align_of::<ChunkFooter>() <= CHUNK_ALIGN;
+const _: [(); _FOOTER_ALIGN_ASSERTION as usize] = [()];
+
+// Maximum typical overhead per allocation imposed by allocators.
+const MALLOC_OVERHEAD: usize = 16;
+
+// This is the overhead from malloc, footer and alignment. For instance, if
+// we want to request a chunk of memory that has at least X bytes usable for
+// allocations (where X is aligned to CHUNK_ALIGN), then we expect that the
+// after adding a footer, malloc overhead and alignment, the chunk of memory
+// the allocator actually sets aside for us is X+OVERHEAD rounded up to the
+// nearest suitable size boundary.
+const OVERHEAD: usize = (MALLOC_OVERHEAD + FOOTER_SIZE + (CHUNK_ALIGN - 1)) & !(CHUNK_ALIGN - 1);
+
+// Choose a relatively small default initial chunk size, since we double chunk
+// sizes as we grow bump arenas to amortize costs of hitting the global
+// allocator.
+const FIRST_ALLOCATION_GOAL: usize = 1 << 9;
+
+// The actual size of the first allocation is going to be a bit smaller
+// than the goal. We need to make room for the footer, and we also need
+// take the alignment into account.
+const DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER: usize = FIRST_ALLOCATION_GOAL - OVERHEAD;
+
+/// The memory size and alignment details for a potential new chunk
+/// allocation.
+#[derive(Debug, Clone, Copy)]
+struct NewChunkMemoryDetails {
+    new_size_without_footer: usize,
+    align: usize,
+    size: usize,
+}
+
+/// Wrapper around `Layout::from_size_align` that adds debug assertions.
+#[inline]
+unsafe fn layout_from_size_align(size: usize, align: usize) -> Layout {
+    if cfg!(debug_assertions) {
+        Layout::from_size_align(size, align).unwrap()
+    } else {
+        Layout::from_size_align_unchecked(size, align)
+    }
+}
+
+#[inline(never)]
+fn allocation_size_overflow<T>() -> T {
+    panic!("requested allocation size overflowed")
+}
+
+// This can be migrated to directly use `usize::abs_diff` when the MSRV
+// reaches `1.60`
+fn abs_diff(a: usize, b: usize) -> usize {
+    usize::max(a, b) - usize::min(a, b)
+}
+
+impl Bump {
+    /// Construct a new arena to bump allocate into.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// # let _ = bump;
+    /// ```
+    pub fn new() -> Bump {
+        Self::with_capacity(0)
+    }
+
+    /// Attempt to construct a new arena to bump allocate into.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::try_new();
+    /// # let _ = bump.unwrap();
+    /// ```
+    pub fn try_new() -> Result<Bump, AllocErr> {
+        Bump::try_with_capacity(0)
+    }
+
+    /// Construct a new arena with the specified byte capacity to bump allocate into.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::with_capacity(100);
+    /// # let _ = bump;
+    /// ```
+    pub fn with_capacity(capacity: usize) -> Bump {
+        Bump::try_with_capacity(capacity).unwrap_or_else(|_| oom())
+    }
+
+    /// Attempt to construct a new arena with the specified byte capacity to bump allocate into.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::try_with_capacity(100);
+    /// # let _ = bump.unwrap();
+    /// ```
+    pub fn try_with_capacity(capacity: usize) -> Result<Self, AllocErr> {
+        if capacity == 0 {
+            return Ok(Bump {
+                current_chunk_footer: Cell::new(EMPTY_CHUNK.get()),
+                allocation_limit: Cell::new(None),
+            });
+        }
+
+        let layout = unsafe { layout_from_size_align(capacity, 1) };
+
+        let chunk_footer = unsafe {
+            Self::new_chunk(
+                Bump::new_chunk_memory_details(None, layout).ok_or(AllocErr)?,
+                layout,
+                EMPTY_CHUNK.get(),
+            )
+            .ok_or(AllocErr)?
+        };
+
+        Ok(Bump {
+            current_chunk_footer: Cell::new(chunk_footer),
+            allocation_limit: Cell::new(None),
+        })
+    }
+
+    /// The allocation limit for this arena in bytes.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::with_capacity(0);
+    ///
+    /// assert_eq!(bump.allocation_limit(), None);
+    ///
+    /// bump.set_allocation_limit(Some(6));
+    ///
+    /// assert_eq!(bump.allocation_limit(), Some(6));
+    ///
+    /// bump.set_allocation_limit(None);
+    ///
+    /// assert_eq!(bump.allocation_limit(), None);
+    /// ```
+    pub fn allocation_limit(&self) -> Option<usize> {
+        self.allocation_limit.get()
+    }
+
+    /// Set the allocation limit in bytes for this arena.
+    ///
+    /// The allocation limit is only enforced when allocating new backing chunks for
+    /// a `Bump`. Updating the allocation limit will not affect existing allocations
+    /// or any future allocations within the `Bump`'s current chunk.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::with_capacity(0);
+    ///
+    /// bump.set_allocation_limit(Some(0));
+    ///
+    /// assert!(bump.try_alloc(5).is_err());
+    /// ```
+    pub fn set_allocation_limit(&self, limit: Option<usize>) {
+        self.allocation_limit.set(limit)
+    }
+
+    /// How much headroom an arena has before it hits its allocation
+    /// limit.
+    fn allocation_limit_remaining(&self) -> Option<usize> {
+        self.allocation_limit.get().and_then(|allocation_limit| {
+            let allocated_bytes = self.allocated_bytes();
+            if allocated_bytes > allocation_limit {
+                None
+            } else {
+                Some(abs_diff(allocation_limit, allocated_bytes))
+            }
+        })
+    }
+
+    /// Whether a request to allocate a new chunk with a given size for a given
+    /// requested layout will fit under the allocation limit set on a `Bump`.
+    fn chunk_fits_under_limit(
+        allocation_limit_remaining: Option<usize>,
+        new_chunk_memory_details: NewChunkMemoryDetails,
+    ) -> bool {
+        allocation_limit_remaining
+            .map(|allocation_limit_left| {
+                allocation_limit_left >= new_chunk_memory_details.new_size_without_footer
+            })
+            .unwrap_or(true)
+    }
+
+    /// Determine the memory details including final size, alignment and
+    /// final size without footer for a new chunk that would be allocated
+    /// to fulfill an allocation request.
+    fn new_chunk_memory_details(
+        new_size_without_footer: Option<usize>,
+        requested_layout: Layout,
+    ) -> Option<NewChunkMemoryDetails> {
+        let mut new_size_without_footer =
+            new_size_without_footer.unwrap_or(DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER);
+
+        // We want to have CHUNK_ALIGN or better alignment
+        let mut align = CHUNK_ALIGN;
+
+        // If we already know we need to fulfill some request,
+        // make sure we allocate at least enough to satisfy it
+        align = align.max(requested_layout.align());
+        let requested_size =
+            round_up_to(requested_layout.size(), align).unwrap_or_else(allocation_size_overflow);
+        new_size_without_footer = new_size_without_footer.max(requested_size);
+
+        // We want our allocations to play nice with the memory allocator,
+        // and waste as little memory as possible.
+        // For small allocations, this means that the entire allocation
+        // including the chunk footer and mallocs internal overhead is
+        // as close to a power of two as we can go without going over.
+        // For larger allocations, we only need to get close to a page
+        // boundary without going over.
+        if new_size_without_footer < PAGE_STRATEGY_CUTOFF {
+            new_size_without_footer =
+                (new_size_without_footer + OVERHEAD).next_power_of_two() - OVERHEAD;
+        } else {
+            new_size_without_footer =
+                round_up_to(new_size_without_footer + OVERHEAD, 0x1000)? - OVERHEAD;
+        }
+
+        debug_assert_eq!(align % CHUNK_ALIGN, 0);
+        debug_assert_eq!(new_size_without_footer % CHUNK_ALIGN, 0);
+        let size = new_size_without_footer
+            .checked_add(FOOTER_SIZE)
+            .unwrap_or_else(allocation_size_overflow);
+
+        Some(NewChunkMemoryDetails {
+            new_size_without_footer,
+            size,
+            align,
+        })
+    }
+
+    /// Allocate a new chunk and return its initialized footer.
+    ///
+    /// If given, `layouts` is a tuple of the current chunk size and the
+    /// layout of the allocation request that triggered us to fall back to
+    /// allocating a new chunk of memory.
+    unsafe fn new_chunk(
+        new_chunk_memory_details: NewChunkMemoryDetails,
+        requested_layout: Layout,
+        prev: NonNull<ChunkFooter>,
+    ) -> Option<NonNull<ChunkFooter>> {
+        let NewChunkMemoryDetails {
+            new_size_without_footer,
+            align,
+            size,
+        } = new_chunk_memory_details;
+
+        let layout = layout_from_size_align(size, align);
+
+        debug_assert!(size >= requested_layout.size());
+
+        let data = alloc(layout);
+        let data = NonNull::new(data)?;
+
+        // The `ChunkFooter` is at the end of the chunk.
+        let footer_ptr = data.as_ptr().add(new_size_without_footer);
+        debug_assert_eq!((data.as_ptr() as usize) % align, 0);
+        debug_assert_eq!(footer_ptr as usize % CHUNK_ALIGN, 0);
+        let footer_ptr = footer_ptr as *mut ChunkFooter;
+
+        // The bump pointer is initialized to the end of the range we will
+        // bump out of.
+        let ptr = Cell::new(NonNull::new_unchecked(footer_ptr as *mut u8));
+
+        // The `allocated_bytes` of a new chunk counts the total size
+        // of the chunks, not how much of the chunks are used.
+        let allocated_bytes = prev.as_ref().allocated_bytes + new_size_without_footer;
+
+        ptr::write(
+            footer_ptr,
+            ChunkFooter {
+                data,
+                layout,
+                prev: Cell::new(prev),
+                ptr,
+                allocated_bytes,
+            },
+        );
+
+        Some(NonNull::new_unchecked(footer_ptr))
+    }
+
+    /// Reset this bump allocator.
+    ///
+    /// Performs mass deallocation on everything allocated in this arena by
+    /// resetting the pointer into the underlying chunk of memory to the start
+    /// of the chunk. Does not run any `Drop` implementations on deallocated
+    /// objects; see [the top-level documentation](struct.Bump.html) for details.
+    ///
+    /// If this arena has allocated multiple chunks to bump allocate into, then
+    /// the excess chunks are returned to the global allocator.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let mut bump = bumpalo::Bump::new();
+    ///
+    /// // Allocate a bunch of things.
+    /// {
+    ///     for i in 0..100 {
+    ///         bump.alloc(i);
+    ///     }
+    /// }
+    ///
+    /// // Reset the arena.
+    /// bump.reset();
+    ///
+    /// // Allocate some new things in the space previously occupied by the
+    /// // original things.
+    /// for j in 200..400 {
+    ///     bump.alloc(j);
+    /// }
+    ///```
+    pub fn reset(&mut self) {
+        // Takes `&mut self` so `self` must be unique and there can't be any
+        // borrows active that would get invalidated by resetting.
+        unsafe {
+            if self.current_chunk_footer.get().as_ref().is_empty() {
+                return;
+            }
+
+            let mut cur_chunk = self.current_chunk_footer.get();
+
+            // Deallocate all chunks except the current one
+            let prev_chunk = cur_chunk.as_ref().prev.replace(EMPTY_CHUNK.get());
+            dealloc_chunk_list(prev_chunk);
+
+            // Reset the bump finger to the end of the chunk.
+            cur_chunk.as_ref().ptr.set(cur_chunk.cast());
+
+            // Reset the allocated size of the chunk.
+            cur_chunk.as_mut().allocated_bytes = cur_chunk.as_ref().layout.size();
+
+            debug_assert!(
+                self.current_chunk_footer
+                    .get()
+                    .as_ref()
+                    .prev
+                    .get()
+                    .as_ref()
+                    .is_empty(),
+                "We should only have a single chunk"
+            );
+            debug_assert_eq!(
+                self.current_chunk_footer.get().as_ref().ptr.get(),
+                self.current_chunk_footer.get().cast(),
+                "Our chunk's bump finger should be reset to the start of its allocation"
+            );
+        }
+    }
+
+    /// Allocate an object in this `Bump` and return an exclusive reference to
+    /// it.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for `T` fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.alloc("hello");
+    /// assert_eq!(*x, "hello");
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc<T>(&self, val: T) -> &mut T {
+        self.alloc_with(|| val)
+    }
+
+    /// Try to allocate an object in this `Bump` and return an exclusive
+    /// reference to it.
+    ///
+    /// ## Errors
+    ///
+    /// Errors if reserving space for `T` fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.try_alloc("hello");
+    /// assert_eq!(x, Ok(&mut "hello"));
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn try_alloc<T>(&self, val: T) -> Result<&mut T, AllocErr> {
+        self.try_alloc_with(|| val)
+    }
+
+    /// Pre-allocate space for an object in this `Bump`, initializes it using
+    /// the closure, then returns an exclusive reference to it.
+    ///
+    /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a
+    /// discussion on the differences between the `_with` suffixed methods and
+    /// those methods without it, their performance characteristics, and when
+    /// you might or might not choose a `_with` suffixed method.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for `T` fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.alloc_with(|| "hello");
+    /// assert_eq!(*x, "hello");
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_with<F, T>(&self, f: F) -> &mut T
+    where
+        F: FnOnce() -> T,
+    {
+        #[inline(always)]
+        unsafe fn inner_writer<T, F>(ptr: *mut T, f: F)
+        where
+            F: FnOnce() -> T,
+        {
+            // This function is translated as:
+            // - allocate space for a T on the stack
+            // - call f() with the return value being put onto this stack space
+            // - memcpy from the stack to the heap
+            //
+            // Ideally we want LLVM to always realize that doing a stack
+            // allocation is unnecessary and optimize the code so it writes
+            // directly into the heap instead. It seems we get it to realize
+            // this most consistently if we put this critical line into it's
+            // own function instead of inlining it into the surrounding code.
+            ptr::write(ptr, f())
+        }
+
+        let layout = Layout::new::<T>();
+
+        unsafe {
+            let p = self.alloc_layout(layout);
+            let p = p.as_ptr() as *mut T;
+            inner_writer(p, f);
+            &mut *p
+        }
+    }
+
+    /// Tries to pre-allocate space for an object in this `Bump`, initializes
+    /// it using the closure, then returns an exclusive reference to it.
+    ///
+    /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a
+    /// discussion on the differences between the `_with` suffixed methods and
+    /// those methods without it, their performance characteristics, and when
+    /// you might or might not choose a `_with` suffixed method.
+    ///
+    /// ## Errors
+    ///
+    /// Errors if reserving space for `T` fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.try_alloc_with(|| "hello");
+    /// assert_eq!(x, Ok(&mut "hello"));
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn try_alloc_with<F, T>(&self, f: F) -> Result<&mut T, AllocErr>
+    where
+        F: FnOnce() -> T,
+    {
+        #[inline(always)]
+        unsafe fn inner_writer<T, F>(ptr: *mut T, f: F)
+        where
+            F: FnOnce() -> T,
+        {
+            // This function is translated as:
+            // - allocate space for a T on the stack
+            // - call f() with the return value being put onto this stack space
+            // - memcpy from the stack to the heap
+            //
+            // Ideally we want LLVM to always realize that doing a stack
+            // allocation is unnecessary and optimize the code so it writes
+            // directly into the heap instead. It seems we get it to realize
+            // this most consistently if we put this critical line into it's
+            // own function instead of inlining it into the surrounding code.
+            ptr::write(ptr, f())
+        }
+
+        //SAFETY: Self-contained:
+        // `p` is allocated for `T` and then a `T` is written.
+        let layout = Layout::new::<T>();
+        let p = self.try_alloc_layout(layout)?;
+        let p = p.as_ptr() as *mut T;
+
+        unsafe {
+            inner_writer(p, f);
+            Ok(&mut *p)
+        }
+    }
+
+    /// Pre-allocates space for a [`Result`] in this `Bump`, initializes it using
+    /// the closure, then returns an exclusive reference to its `T` if [`Ok`].
+    ///
+    /// Iff the allocation fails, the closure is not run.
+    ///
+    /// Iff [`Err`], an allocator rewind is *attempted* and the `E` instance is
+    /// moved out of the allocator to be consumed or dropped as normal.
+    ///
+    /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a
+    /// discussion on the differences between the `_with` suffixed methods and
+    /// those methods without it, their performance characteristics, and when
+    /// you might or might not choose a `_with` suffixed method.
+    ///
+    /// For caveats specific to fallible initialization, see
+    /// [The `_try_with` Method Suffix](#fallible-initialization-the-_try_with-method-suffix).
+    ///
+    /// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html
+    /// [`Ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Ok
+    /// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
+    ///
+    /// ## Errors
+    ///
+    /// Iff the allocation succeeds but `f` fails, that error is forwarded by value.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for `Result<T, E>` fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.alloc_try_with(|| Ok("hello"))?;
+    /// assert_eq!(*x, "hello");
+    /// # Result::<_, ()>::Ok(())
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_try_with<F, T, E>(&self, f: F) -> Result<&mut T, E>
+    where
+        F: FnOnce() -> Result<T, E>,
+    {
+        let rewind_footer = self.current_chunk_footer.get();
+        let rewind_ptr = unsafe { rewind_footer.as_ref() }.ptr.get();
+        let mut inner_result_ptr = NonNull::from(self.alloc_with(f));
+        match unsafe { inner_result_ptr.as_mut() } {
+            Ok(t) => Ok(unsafe {
+                //SAFETY:
+                // The `&mut Result<T, E>` returned by `alloc_with` may be
+                // lifetime-limited by `E`, but the derived `&mut T` still has
+                // the same validity as in `alloc_with` since the error variant
+                // is already ruled out here.
+
+                // We could conditionally truncate the allocation here, but
+                // since it grows backwards, it seems unlikely that we'd get
+                // any more than the `Result`'s discriminant this way, if
+                // anything at all.
+                &mut *(t as *mut _)
+            }),
+            Err(e) => unsafe {
+                // If this result was the last allocation in this arena, we can
+                // reclaim its space. In fact, sometimes we can do even better
+                // than simply calling `dealloc` on the result pointer: we can
+                // reclaim any alignment padding we might have added (which
+                // `dealloc` cannot do) if we didn't allocate a new chunk for
+                // this result.
+                if self.is_last_allocation(inner_result_ptr.cast()) {
+                    let current_footer_p = self.current_chunk_footer.get();
+                    let current_ptr = &current_footer_p.as_ref().ptr;
+                    if current_footer_p == rewind_footer {
+                        // It's still the same chunk, so reset the bump pointer
+                        // to its original value upon entry to this method
+                        // (reclaiming any alignment padding we may have
+                        // added).
+                        current_ptr.set(rewind_ptr);
+                    } else {
+                        // We allocated a new chunk for this result.
+                        //
+                        // We know the result is the only allocation in this
+                        // chunk: Any additional allocations since the start of
+                        // this method could only have happened when running
+                        // the initializer function, which is called *after*
+                        // reserving space for this result. Therefore, since we
+                        // already determined via the check above that this
+                        // result was the last allocation, there must not have
+                        // been any other allocations, and this result is the
+                        // only allocation in this chunk.
+                        //
+                        // Because this is the only allocation in this chunk,
+                        // we can reset the chunk's bump finger to the start of
+                        // the chunk.
+                        current_ptr.set(current_footer_p.as_ref().data);
+                    }
+                }
+                //SAFETY:
+                // As we received `E` semantically by value from `f`, we can
+                // just copy that value here as long as we avoid a double-drop
+                // (which can't happen as any specific references to the `E`'s
+                // data in `self` are destroyed when this function returns).
+                //
+                // The order between this and the deallocation doesn't matter
+                // because `Self: !Sync`.
+                Err(ptr::read(e as *const _))
+            },
+        }
+    }
+
+    /// Tries to pre-allocates space for a [`Result`] in this `Bump`,
+    /// initializes it using the closure, then returns an exclusive reference
+    /// to its `T` if all [`Ok`].
+    ///
+    /// Iff the allocation fails, the closure is not run.
+    ///
+    /// Iff the closure returns [`Err`], an allocator rewind is *attempted* and
+    /// the `E` instance is moved out of the allocator to be consumed or dropped
+    /// as normal.
+    ///
+    /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a
+    /// discussion on the differences between the `_with` suffixed methods and
+    /// those methods without it, their performance characteristics, and when
+    /// you might or might not choose a `_with` suffixed method.
+    ///
+    /// For caveats specific to fallible initialization, see
+    /// [The `_try_with` Method Suffix](#fallible-initialization-the-_try_with-method-suffix).
+    ///
+    /// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html
+    /// [`Ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Ok
+    /// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
+    ///
+    /// ## Errors
+    ///
+    /// Errors with the [`Alloc`](`AllocOrInitError::Alloc`) variant iff
+    /// reserving space for `Result<T, E>` fails.
+    ///
+    /// Iff the allocation succeeds but `f` fails, that error is forwarded by
+    /// value inside the [`Init`](`AllocOrInitError::Init`) variant.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.try_alloc_try_with(|| Ok("hello"))?;
+    /// assert_eq!(*x, "hello");
+    /// # Result::<_, bumpalo::AllocOrInitError<()>>::Ok(())
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn try_alloc_try_with<F, T, E>(&self, f: F) -> Result<&mut T, AllocOrInitError<E>>
+    where
+        F: FnOnce() -> Result<T, E>,
+    {
+        let rewind_footer = self.current_chunk_footer.get();
+        let rewind_ptr = unsafe { rewind_footer.as_ref() }.ptr.get();
+        let mut inner_result_ptr = NonNull::from(self.try_alloc_with(f)?);
+        match unsafe { inner_result_ptr.as_mut() } {
+            Ok(t) => Ok(unsafe {
+                //SAFETY:
+                // The `&mut Result<T, E>` returned by `alloc_with` may be
+                // lifetime-limited by `E`, but the derived `&mut T` still has
+                // the same validity as in `alloc_with` since the error variant
+                // is already ruled out here.
+
+                // We could conditionally truncate the allocation here, but
+                // since it grows backwards, it seems unlikely that we'd get
+                // any more than the `Result`'s discriminant this way, if
+                // anything at all.
+                &mut *(t as *mut _)
+            }),
+            Err(e) => unsafe {
+                // If this result was the last allocation in this arena, we can
+                // reclaim its space. In fact, sometimes we can do even better
+                // than simply calling `dealloc` on the result pointer: we can
+                // reclaim any alignment padding we might have added (which
+                // `dealloc` cannot do) if we didn't allocate a new chunk for
+                // this result.
+                if self.is_last_allocation(inner_result_ptr.cast()) {
+                    let current_footer_p = self.current_chunk_footer.get();
+                    let current_ptr = &current_footer_p.as_ref().ptr;
+                    if current_footer_p == rewind_footer {
+                        // It's still the same chunk, so reset the bump pointer
+                        // to its original value upon entry to this method
+                        // (reclaiming any alignment padding we may have
+                        // added).
+                        current_ptr.set(rewind_ptr);
+                    } else {
+                        // We allocated a new chunk for this result.
+                        //
+                        // We know the result is the only allocation in this
+                        // chunk: Any additional allocations since the start of
+                        // this method could only have happened when running
+                        // the initializer function, which is called *after*
+                        // reserving space for this result. Therefore, since we
+                        // already determined via the check above that this
+                        // result was the last allocation, there must not have
+                        // been any other allocations, and this result is the
+                        // only allocation in this chunk.
+                        //
+                        // Because this is the only allocation in this chunk,
+                        // we can reset the chunk's bump finger to the start of
+                        // the chunk.
+                        current_ptr.set(current_footer_p.as_ref().data);
+                    }
+                }
+                //SAFETY:
+                // As we received `E` semantically by value from `f`, we can
+                // just copy that value here as long as we avoid a double-drop
+                // (which can't happen as any specific references to the `E`'s
+                // data in `self` are destroyed when this function returns).
+                //
+                // The order between this and the deallocation doesn't matter
+                // because `Self: !Sync`.
+                Err(AllocOrInitError::Init(ptr::read(e as *const _)))
+            },
+        }
+    }
+
+    /// `Copy` a slice into this `Bump` and return an exclusive reference to
+    /// the copy.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the slice fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.alloc_slice_copy(&[1, 2, 3]);
+    /// assert_eq!(x, &[1, 2, 3]);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_slice_copy<T>(&self, src: &[T]) -> &mut [T]
+    where
+        T: Copy,
+    {
+        let layout = Layout::for_value(src);
+        let dst = self.alloc_layout(layout).cast::<T>();
+
+        unsafe {
+            ptr::copy_nonoverlapping(src.as_ptr(), dst.as_ptr(), src.len());
+            slice::from_raw_parts_mut(dst.as_ptr(), src.len())
+        }
+    }
+
+    /// `Clone` a slice into this `Bump` and return an exclusive reference to
+    /// the clone. Prefer [`alloc_slice_copy`](#method.alloc_slice_copy) if `T` is `Copy`.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the slice fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// #[derive(Clone, Debug, Eq, PartialEq)]
+    /// struct Sheep {
+    ///     name: String,
+    /// }
+    ///
+    /// let originals = [
+    ///     Sheep { name: "Alice".into() },
+    ///     Sheep { name: "Bob".into() },
+    ///     Sheep { name: "Cathy".into() },
+    /// ];
+    ///
+    /// let bump = bumpalo::Bump::new();
+    /// let clones = bump.alloc_slice_clone(&originals);
+    /// assert_eq!(originals, clones);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_slice_clone<T>(&self, src: &[T]) -> &mut [T]
+    where
+        T: Clone,
+    {
+        let layout = Layout::for_value(src);
+        let dst = self.alloc_layout(layout).cast::<T>();
+
+        unsafe {
+            for (i, val) in src.iter().cloned().enumerate() {
+                ptr::write(dst.as_ptr().add(i), val);
+            }
+
+            slice::from_raw_parts_mut(dst.as_ptr(), src.len())
+        }
+    }
+
+    /// `Copy` a string slice into this `Bump` and return an exclusive reference to it.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the string fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let hello = bump.alloc_str("hello world");
+    /// assert_eq!("hello world", hello);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_str(&self, src: &str) -> &mut str {
+        let buffer = self.alloc_slice_copy(src.as_bytes());
+        unsafe {
+            // This is OK, because it already came in as str, so it is guaranteed to be utf8
+            str::from_utf8_unchecked_mut(buffer)
+        }
+    }
+
+    /// Allocates a new slice of size `len` into this `Bump` and returns an
+    /// exclusive reference to the copy.
+    ///
+    /// The elements of the slice are initialized using the supplied closure.
+    /// The closure argument is the position in the slice.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the slice fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.alloc_slice_fill_with(5, |i| 5 * (i + 1));
+    /// assert_eq!(x, &[5, 10, 15, 20, 25]);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_slice_fill_with<T, F>(&self, len: usize, mut f: F) -> &mut [T]
+    where
+        F: FnMut(usize) -> T,
+    {
+        let layout = Layout::array::<T>(len).unwrap_or_else(|_| oom());
+        let dst = self.alloc_layout(layout).cast::<T>();
+
+        unsafe {
+            for i in 0..len {
+                ptr::write(dst.as_ptr().add(i), f(i));
+            }
+
+            let result = slice::from_raw_parts_mut(dst.as_ptr(), len);
+            debug_assert_eq!(Layout::for_value(result), layout);
+            result
+        }
+    }
+
+    /// Allocates a new slice of size `len` into this `Bump` and returns an
+    /// exclusive reference to the copy.
+    ///
+    /// All elements of the slice are initialized to `value`.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the slice fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.alloc_slice_fill_copy(5, 42);
+    /// assert_eq!(x, &[42, 42, 42, 42, 42]);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_slice_fill_copy<T: Copy>(&self, len: usize, value: T) -> &mut [T] {
+        self.alloc_slice_fill_with(len, |_| value)
+    }
+
+    /// Allocates a new slice of size `len` slice into this `Bump` and return an
+    /// exclusive reference to the copy.
+    ///
+    /// All elements of the slice are initialized to `value.clone()`.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the slice fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let s: String = "Hello Bump!".to_string();
+    /// let x: &[String] = bump.alloc_slice_fill_clone(2, &s);
+    /// assert_eq!(x.len(), 2);
+    /// assert_eq!(&x[0], &s);
+    /// assert_eq!(&x[1], &s);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_slice_fill_clone<T: Clone>(&self, len: usize, value: &T) -> &mut [T] {
+        self.alloc_slice_fill_with(len, |_| value.clone())
+    }
+
+    /// Allocates a new slice of size `len` slice into this `Bump` and return an
+    /// exclusive reference to the copy.
+    ///
+    /// The elements are initialized using the supplied iterator.
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the slice fails, or if the supplied
+    /// iterator returns fewer elements than it promised.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x: &[i32] = bump.alloc_slice_fill_iter([2, 3, 5].iter().cloned().map(|i| i * i));
+    /// assert_eq!(x, [4, 9, 25]);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_slice_fill_iter<T, I>(&self, iter: I) -> &mut [T]
+    where
+        I: IntoIterator<Item = T>,
+        I::IntoIter: ExactSizeIterator,
+    {
+        let mut iter = iter.into_iter();
+        self.alloc_slice_fill_with(iter.len(), |_| {
+            iter.next().expect("Iterator supplied too few elements")
+        })
+    }
+
+    /// Allocates a new slice of size `len` slice into this `Bump` and return an
+    /// exclusive reference to the copy.
+    ///
+    /// All elements of the slice are initialized to [`T::default()`].
+    ///
+    /// [`T::default()`]: https://doc.rust-lang.org/std/default/trait.Default.html#tymethod.default
+    ///
+    /// ## Panics
+    ///
+    /// Panics if reserving space for the slice fails.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let x = bump.alloc_slice_fill_default::<u32>(5);
+    /// assert_eq!(x, &[0, 0, 0, 0, 0]);
+    /// ```
+    #[inline(always)]
+    #[allow(clippy::mut_from_ref)]
+    pub fn alloc_slice_fill_default<T: Default>(&self, len: usize) -> &mut [T] {
+        self.alloc_slice_fill_with(len, |_| T::default())
+    }
+
+    /// Allocate space for an object with the given `Layout`.
+    ///
+    /// The returned pointer points at uninitialized memory, and should be
+    /// initialized with
+    /// [`std::ptr::write`](https://doc.rust-lang.org/std/ptr/fn.write.html).
+    ///
+    /// # Panics
+    ///
+    /// Panics if reserving space matching `layout` fails.
+    #[inline(always)]
+    pub fn alloc_layout(&self, layout: Layout) -> NonNull<u8> {
+        self.try_alloc_layout(layout).unwrap_or_else(|_| oom())
+    }
+
+    /// Attempts to allocate space for an object with the given `Layout` or else returns
+    /// an `Err`.
+    ///
+    /// The returned pointer points at uninitialized memory, and should be
+    /// initialized with
+    /// [`std::ptr::write`](https://doc.rust-lang.org/std/ptr/fn.write.html).
+    ///
+    /// # Errors
+    ///
+    /// Errors if reserving space matching `layout` fails.
+    #[inline(always)]
+    pub fn try_alloc_layout(&self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
+        if let Some(p) = self.try_alloc_layout_fast(layout) {
+            Ok(p)
+        } else {
+            self.alloc_layout_slow(layout).ok_or(AllocErr)
+        }
+    }
+
+    #[inline(always)]
+    fn try_alloc_layout_fast(&self, layout: Layout) -> Option<NonNull<u8>> {
+        // We don't need to check for ZSTs here since they will automatically
+        // be handled properly: the pointer will be bumped by zero bytes,
+        // modulo alignment. This keeps the fast path optimized for non-ZSTs,
+        // which are much more common.
+        unsafe {
+            let footer = self.current_chunk_footer.get();
+            let footer = footer.as_ref();
+            let ptr = footer.ptr.get().as_ptr();
+            let start = footer.data.as_ptr();
+            debug_assert!(start <= ptr);
+            debug_assert!(ptr as *const u8 <= footer as *const _ as *const u8);
+
+            if (ptr as usize) < layout.size() {
+                return None;
+            }
+
+            let ptr = ptr.wrapping_sub(layout.size());
+            let rem = ptr as usize % layout.align();
+            let aligned_ptr = ptr.wrapping_sub(rem);
+
+            if aligned_ptr >= start {
+                let aligned_ptr = NonNull::new_unchecked(aligned_ptr as *mut u8);
+                footer.ptr.set(aligned_ptr);
+                Some(aligned_ptr)
+            } else {
+                None
+            }
+        }
+    }
+
+    /// Gets the remaining capacity in the current chunk (in bytes).
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// use bumpalo::Bump;
+    ///
+    /// let bump = Bump::with_capacity(100);
+    ///
+    /// let capacity = bump.chunk_capacity();
+    /// assert!(capacity >= 100);
+    /// ```
+    pub fn chunk_capacity(&self) -> usize {
+        let current_footer = self.current_chunk_footer.get();
+        let current_footer = unsafe { current_footer.as_ref() };
+
+        current_footer as *const _ as usize - current_footer.data.as_ptr() as usize
+    }
+
+    /// Slow path allocation for when we need to allocate a new chunk from the
+    /// parent bump set because there isn't enough room in our current chunk.
+    #[inline(never)]
+    fn alloc_layout_slow(&self, layout: Layout) -> Option<NonNull<u8>> {
+        unsafe {
+            let size = layout.size();
+            let allocation_limit_remaining = self.allocation_limit_remaining();
+
+            // Get a new chunk from the global allocator.
+            let current_footer = self.current_chunk_footer.get();
+            let current_layout = current_footer.as_ref().layout;
+
+            // By default, we want our new chunk to be about twice as big
+            // as the previous chunk. If the global allocator refuses it,
+            // we try to divide it by half until it works or the requested
+            // size is smaller than the default footer size.
+            let min_new_chunk_size = layout.size().max(DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER);
+            let mut base_size = (current_layout.size() - FOOTER_SIZE)
+                .checked_mul(2)?
+                .max(min_new_chunk_size);
+            let chunk_memory_details = iter::from_fn(|| {
+                let bypass_min_chunk_size_for_small_limits = match self.allocation_limit() {
+                    Some(limit)
+                        if layout.size() < limit
+                            && base_size >= layout.size()
+                            && limit < DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER
+                            && self.allocated_bytes() == 0 =>
+                    {
+                        true
+                    }
+                    _ => false,
+                };
+
+                if base_size >= min_new_chunk_size || bypass_min_chunk_size_for_small_limits {
+                    let size = base_size;
+                    base_size = base_size / 2;
+                    Bump::new_chunk_memory_details(Some(size), layout)
+                } else {
+                    None
+                }
+            });
+
+            let new_footer = chunk_memory_details
+                .filter_map(|chunk_memory_details| {
+                    if Bump::chunk_fits_under_limit(
+                        allocation_limit_remaining,
+                        chunk_memory_details,
+                    ) {
+                        Bump::new_chunk(chunk_memory_details, layout, current_footer)
+                    } else {
+                        None
+                    }
+                })
+                .next()?;
+
+            debug_assert_eq!(
+                new_footer.as_ref().data.as_ptr() as usize % layout.align(),
+                0
+            );
+
+            // Set the new chunk as our new current chunk.
+            self.current_chunk_footer.set(new_footer);
+
+            let new_footer = new_footer.as_ref();
+
+            // Move the bump ptr finger down to allocate room for `val`. We know
+            // this can't overflow because we successfully allocated a chunk of
+            // at least the requested size.
+            let mut ptr = new_footer.ptr.get().as_ptr().sub(size);
+            // Round the pointer down to the requested alignment.
+            ptr = ptr.sub(ptr as usize % layout.align());
+            debug_assert!(
+                ptr as *const _ <= new_footer,
+                "{:p} <= {:p}",
+                ptr,
+                new_footer
+            );
+            let ptr = NonNull::new_unchecked(ptr as *mut u8);
+            new_footer.ptr.set(ptr);
+
+            // Return a pointer to the freshly allocated region in this chunk.
+            Some(ptr)
+        }
+    }
+
+    /// Returns an iterator over each chunk of allocated memory that
+    /// this arena has bump allocated into.
+    ///
+    /// The chunks are returned ordered by allocation time, with the most
+    /// recently allocated chunk being returned first, and the least recently
+    /// allocated chunk being returned last.
+    ///
+    /// The values inside each chunk are also ordered by allocation time, with
+    /// the most recent allocation being earlier in the slice, and the least
+    /// recent allocation being towards the end of the slice.
+    ///
+    /// ## Safety
+    ///
+    /// Because this method takes `&mut self`, we know that the bump arena
+    /// reference is unique and therefore there aren't any active references to
+    /// any of the objects we've allocated in it either. This potential aliasing
+    /// of exclusive references is one common footgun for unsafe code that we
+    /// don't need to worry about here.
+    ///
+    /// However, there could be regions of uninitialized memory used as padding
+    /// between allocations, which is why this iterator has items of type
+    /// `[MaybeUninit<u8>]`, instead of simply `[u8]`.
+    ///
+    /// The only way to guarantee that there is no padding between allocations
+    /// or within allocated objects is if all of these properties hold:
+    ///
+    /// 1. Every object allocated in this arena has the same alignment,
+    ///    and that alignment is at most 16.
+    /// 2. Every object's size is a multiple of its alignment.
+    /// 3. None of the objects allocated in this arena contain any internal
+    ///    padding.
+    ///
+    /// If you want to use this `iter_allocated_chunks` method, it is *your*
+    /// responsibility to ensure that these properties hold before calling
+    /// `MaybeUninit::assume_init` or otherwise reading the returned values.
+    ///
+    /// Finally, you must also ensure that any values allocated into the bump
+    /// arena have not had their `Drop` implementations called on them,
+    /// e.g. after dropping a [`bumpalo::boxed::Box<T>`][crate::boxed::Box].
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let mut bump = bumpalo::Bump::new();
+    ///
+    /// // Allocate a bunch of `i32`s in this bump arena, potentially causing
+    /// // additional memory chunks to be reserved.
+    /// for i in 0..10000 {
+    ///     bump.alloc(i);
+    /// }
+    ///
+    /// // Iterate over each chunk we've bump allocated into. This is safe
+    /// // because we have only allocated `i32`s in this arena, which fulfills
+    /// // the above requirements.
+    /// for ch in bump.iter_allocated_chunks() {
+    ///     println!("Used a chunk that is {} bytes long", ch.len());
+    ///     println!("The first byte is {:?}", unsafe {
+    ///         ch[0].assume_init()
+    ///     });
+    /// }
+    ///
+    /// // Within a chunk, allocations are ordered from most recent to least
+    /// // recent. If we allocated 'a', then 'b', then 'c', when we iterate
+    /// // through the chunk's data, we get them in the order 'c', then 'b',
+    /// // then 'a'.
+    ///
+    /// bump.reset();
+    /// bump.alloc(b'a');
+    /// bump.alloc(b'b');
+    /// bump.alloc(b'c');
+    ///
+    /// assert_eq!(bump.iter_allocated_chunks().count(), 1);
+    /// let chunk = bump.iter_allocated_chunks().nth(0).unwrap();
+    /// assert_eq!(chunk.len(), 3);
+    ///
+    /// // Safe because we've only allocated `u8`s in this arena, which
+    /// // fulfills the above requirements.
+    /// unsafe {
+    ///     assert_eq!(chunk[0].assume_init(), b'c');
+    ///     assert_eq!(chunk[1].assume_init(), b'b');
+    ///     assert_eq!(chunk[2].assume_init(), b'a');
+    /// }
+    /// ```
+    pub fn iter_allocated_chunks(&mut self) -> ChunkIter<'_> {
+        // SAFE: Ensured by mutable borrow of `self`.
+        let raw = unsafe { self.iter_allocated_chunks_raw() };
+        ChunkIter {
+            raw,
+            bump: PhantomData,
+        }
+    }
+
+    /// Returns an iterator over raw pointers to chunks of allocated memory that
+    /// this arena has bump allocated into.
+    ///
+    /// This is an unsafe version of [`iter_allocated_chunks()`](Bump::iter_allocated_chunks),
+    /// with the caller responsible for safe usage of the returned pointers as
+    /// well as ensuring that the iterator is not invalidated by new
+    /// allocations.
+    ///
+    /// ## Safety
+    ///
+    /// Allocations from this arena must not be performed while the returned
+    /// iterator is alive. If reading the chunk data (or casting to a reference)
+    /// the caller must ensure that there exist no mutable references to
+    /// previously allocated data.
+    ///
+    /// In addition, all of the caveats when reading the chunk data from
+    /// [`iter_allocated_chunks()`](Bump::iter_allocated_chunks) still apply.
+    pub unsafe fn iter_allocated_chunks_raw(&self) -> ChunkRawIter<'_> {
+        ChunkRawIter {
+            footer: self.current_chunk_footer.get(),
+            bump: PhantomData,
+        }
+    }
+
+    /// Calculates the number of bytes currently allocated across all chunks in
+    /// this bump arena.
+    ///
+    /// If you allocate types of different alignments or types with
+    /// larger-than-typical alignment in the same arena, some padding
+    /// bytes might get allocated in the bump arena. Note that those padding
+    /// bytes will add to this method's resulting sum, so you cannot rely
+    /// on it only counting the sum of the sizes of the things
+    /// you've allocated in the arena.
+    ///
+    /// The allocated bytes do not include the size of bumpalo's metadata,
+    /// so the amount of memory requested from the Rust allocator is higher
+    /// than the returned value.
+    ///
+    /// ## Example
+    ///
+    /// ```
+    /// let bump = bumpalo::Bump::new();
+    /// let _x = bump.alloc_slice_fill_default::<u32>(5);
+    /// let bytes = bump.allocated_bytes();
+    /// assert!(bytes >= core::mem::size_of::<u32>() * 5);
+    /// ```
+    pub fn allocated_bytes(&self) -> usize {
+        let footer = self.current_chunk_footer.get();
+
+        unsafe { footer.as_ref().allocated_bytes }
+    }
+
+    #[inline]
+    unsafe fn is_last_allocation(&self, ptr: NonNull<u8>) -> bool {
+        let footer = self.current_chunk_footer.get();
+        let footer = footer.as_ref();
+        footer.ptr.get() == ptr
+    }
+
+    #[inline]
+    unsafe fn dealloc(&self, ptr: NonNull<u8>, layout: Layout) {
+        // If the pointer is the last allocation we made, we can reuse the bytes,
+        // otherwise they are simply leaked -- at least until somebody calls reset().
+        if self.is_last_allocation(ptr) {
+            let ptr = NonNull::new_unchecked(ptr.as_ptr().add(layout.size()));
+            self.current_chunk_footer.get().as_ref().ptr.set(ptr);
+        }
+    }
+
+    #[inline]
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<u8>, AllocErr> {
+        let old_size = old_layout.size();
+        let new_size = new_layout.size();
+        let align_is_compatible = old_layout.align() >= new_layout.align();
+
+        if !align_is_compatible {
+            return Err(AllocErr);
+        }
+
+        // This is how much space we would *actually* reclaim while satisfying
+        // the requested alignment.
+        let delta = round_down_to(old_size - new_size, new_layout.align());
+
+        if self.is_last_allocation(ptr)
+                // Only reclaim the excess space (which requires a copy) if it
+                // is worth it: we are actually going to recover "enough" space
+                // and we can do a non-overlapping copy.
+                && delta >= old_size / 2
+        {
+            let footer = self.current_chunk_footer.get();
+            let footer = footer.as_ref();
+
+            // NB: new_ptr is aligned, because ptr *has to* be aligned, and we
+            // made sure delta is aligned.
+            let new_ptr = NonNull::new_unchecked(footer.ptr.get().as_ptr().add(delta));
+            footer.ptr.set(new_ptr);
+
+            // NB: we know it is non-overlapping because of the size check
+            // in the `if` condition.
+            ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), new_size);
+
+            return Ok(new_ptr);
+        } else {
+            return Ok(ptr);
+        }
+    }
+
+    #[inline]
+    unsafe fn grow(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<u8>, AllocErr> {
+        let old_size = old_layout.size();
+        let new_size = new_layout.size();
+        let align_is_compatible = old_layout.align() >= new_layout.align();
+
+        if align_is_compatible && self.is_last_allocation(ptr) {
+            // Try to allocate the delta size within this same block so we can
+            // reuse the currently allocated space.
+            let delta = new_size - old_size;
+            if let Some(p) =
+                self.try_alloc_layout_fast(layout_from_size_align(delta, old_layout.align()))
+            {
+                ptr::copy(ptr.as_ptr(), p.as_ptr(), old_size);
+                return Ok(p);
+            }
+        }
+
+        // Fallback: do a fresh allocation and copy the existing data into it.
+        let new_ptr = self.try_alloc_layout(new_layout)?;
+        ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), old_size);
+        Ok(new_ptr)
+    }
+}
+
+/// An iterator over each chunk of allocated memory that
+/// an arena has bump allocated into.
+///
+/// The chunks are returned ordered by allocation time, with the most recently
+/// allocated chunk being returned first.
+///
+/// The values inside each chunk are also ordered by allocation time, with the most
+/// recent allocation being earlier in the slice.
+///
+/// This struct is created by the [`iter_allocated_chunks`] method on
+/// [`Bump`]. See that function for a safety description regarding reading from the returned items.
+///
+/// [`Bump`]: struct.Bump.html
+/// [`iter_allocated_chunks`]: struct.Bump.html#method.iter_allocated_chunks
+#[derive(Debug)]
+pub struct ChunkIter<'a> {
+    raw: ChunkRawIter<'a>,
+    bump: PhantomData<&'a mut Bump>,
+}
+
+impl<'a> Iterator for ChunkIter<'a> {
+    type Item = &'a [mem::MaybeUninit<u8>];
+    fn next(&mut self) -> Option<&'a [mem::MaybeUninit<u8>]> {
+        unsafe {
+            let (ptr, len) = self.raw.next()?;
+            let slice = slice::from_raw_parts(ptr as *const mem::MaybeUninit<u8>, len);
+            Some(slice)
+        }
+    }
+}
+
+impl<'a> iter::FusedIterator for ChunkIter<'a> {}
+
+/// An iterator over raw pointers to chunks of allocated memory that this
+/// arena has bump allocated into.
+///
+/// See [`ChunkIter`] for details regarding the returned chunks.
+///
+/// This struct is created by the [`iter_allocated_chunks_raw`] method on
+/// [`Bump`]. See that function for a safety description regarding reading from
+/// the returned items.
+///
+/// [`Bump`]: struct.Bump.html
+/// [`iter_allocated_chunks_raw`]: struct.Bump.html#method.iter_allocated_chunks_raw
+#[derive(Debug)]
+pub struct ChunkRawIter<'a> {
+    footer: NonNull<ChunkFooter>,
+    bump: PhantomData<&'a Bump>,
+}
+
+impl Iterator for ChunkRawIter<'_> {
+    type Item = (*mut u8, usize);
+    fn next(&mut self) -> Option<(*mut u8, usize)> {
+        unsafe {
+            let foot = self.footer.as_ref();
+            if foot.is_empty() {
+                return None;
+            }
+            let (ptr, len) = foot.as_raw_parts();
+            self.footer = foot.prev.get();
+            Some((ptr as *mut u8, len))
+        }
+    }
+}
+
+impl iter::FusedIterator for ChunkRawIter<'_> {}
+
+#[inline(never)]
+#[cold]
+fn oom() -> ! {
+    panic!("out of memory")
+}
+
+unsafe impl<'a> alloc::Alloc for &'a Bump {
+    #[inline(always)]
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
+        self.try_alloc_layout(layout)
+    }
+
+    #[inline]
+    unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
+        Bump::dealloc(self, ptr, layout)
+    }
+
+    #[inline]
+    unsafe fn realloc(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<NonNull<u8>, AllocErr> {
+        let old_size = layout.size();
+
+        if old_size == 0 {
+            return self.try_alloc_layout(layout);
+        }
+
+        let new_layout = layout_from_size_align(new_size, layout.align());
+        if new_size <= old_size {
+            self.shrink(ptr, layout, new_layout)
+        } else {
+            self.grow(ptr, layout, new_layout)
+        }
+    }
+}
+
+#[cfg(feature = "allocator_api")]
+unsafe impl<'a> Allocator for &'a Bump {
+    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
+        self.try_alloc_layout(layout)
+            .map(|p| NonNull::slice_from_raw_parts(p, layout.size()))
+            .map_err(|_| AllocError)
+    }
+
+    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
+        Bump::dealloc(self, ptr, layout)
+    }
+
+    unsafe fn shrink(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        Bump::shrink(self, ptr, old_layout, new_layout)
+            .map(|p| NonNull::slice_from_raw_parts(p, new_layout.size()))
+            .map_err(|_| AllocError)
+    }
+
+    unsafe fn grow(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        Bump::grow(self, ptr, old_layout, new_layout)
+            .map(|p| NonNull::slice_from_raw_parts(p, new_layout.size()))
+            .map_err(|_| AllocError)
+    }
+
+    unsafe fn grow_zeroed(
+        &self,
+        ptr: NonNull<u8>,
+        old_layout: Layout,
+        new_layout: Layout,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        let mut ptr = self.grow(ptr, old_layout, new_layout)?;
+        ptr.as_mut()[old_layout.size()..].fill(0);
+        Ok(ptr)
+    }
+}
+
+// NB: Only tests which require private types, fields, or methods should be in
+// here. Anything that can just be tested via public API surface should be in
+// `bumpalo/tests/all/*`.
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Uses private type `ChunkFooter`.
+    #[test]
+    fn chunk_footer_is_five_words() {
+        assert_eq!(mem::size_of::<ChunkFooter>(), mem::size_of::<usize>() * 6);
+    }
+
+    // Uses private `alloc` module.
+    #[test]
+    #[allow(clippy::cognitive_complexity)]
+    fn test_realloc() {
+        use crate::alloc::Alloc;
+
+        unsafe {
+            const CAPACITY: usize = 1024 - OVERHEAD;
+            let mut b = Bump::with_capacity(CAPACITY);
+
+            // `realloc` doesn't shrink allocations that aren't "worth it".
+            let layout = Layout::from_size_align(100, 1).unwrap();
+            let p = b.alloc_layout(layout);
+            let q = (&b).realloc(p, layout, 51).unwrap();
+            assert_eq!(p, q);
+            b.reset();
+
+            // `realloc` will shrink allocations that are "worth it".
+            let layout = Layout::from_size_align(100, 1).unwrap();
+            let p = b.alloc_layout(layout);
+            let q = (&b).realloc(p, layout, 50).unwrap();
+            assert!(p != q);
+            b.reset();
+
+            // `realloc` will reuse the last allocation when growing.
+            let layout = Layout::from_size_align(10, 1).unwrap();
+            let p = b.alloc_layout(layout);
+            let q = (&b).realloc(p, layout, 11).unwrap();
+            assert_eq!(q.as_ptr() as usize, p.as_ptr() as usize - 1);
+            b.reset();
+
+            // `realloc` will allocate a new chunk when growing the last
+            // allocation, if need be.
+            let layout = Layout::from_size_align(1, 1).unwrap();
+            let p = b.alloc_layout(layout);
+            let q = (&b).realloc(p, layout, CAPACITY + 1).unwrap();
+            assert!(q.as_ptr() as usize != p.as_ptr() as usize - CAPACITY);
+            b = Bump::with_capacity(CAPACITY);
+
+            // `realloc` will allocate and copy when reallocating anything that
+            // wasn't the last allocation.
+            let layout = Layout::from_size_align(1, 1).unwrap();
+            let p = b.alloc_layout(layout);
+            let _ = b.alloc_layout(layout);
+            let q = (&b).realloc(p, layout, 2).unwrap();
+            assert!(q.as_ptr() as usize != p.as_ptr() as usize - 1);
+            b.reset();
+        }
+    }
+
+    // Uses our private `alloc` module.
+    #[test]
+    fn invalid_read() {
+        use alloc::Alloc;
+
+        let mut b = &Bump::new();
+
+        unsafe {
+            let l1 = Layout::from_size_align(12000, 4).unwrap();
+            let p1 = Alloc::alloc(&mut b, l1).unwrap();
+
+            let l2 = Layout::from_size_align(1000, 4).unwrap();
+            Alloc::alloc(&mut b, l2).unwrap();
+
+            let p1 = b.realloc(p1, l1, 24000).unwrap();
+            let l3 = Layout::from_size_align(24000, 4).unwrap();
+            b.realloc(p1, l3, 48000).unwrap();
+        }
+    }
+}