Adding upstream version 110.0.1.upstream/110.0.1upstream

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

10 files changed, 9441 insertions, 0 deletions

diff --git a/third_party/rust/bumpalo/src/alloc.rs b/third_party/rust/bumpalo/src/alloc.rs
new file mode 100644
index 0000000000..0bcc21f22c
--- /dev/null
+++ b/third_party/rust/bumpalo/src/alloc.rs
@@ -0,0 +1,794 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(unstable_name_collisions)]
+#![allow(dead_code)]
+#![allow(deprecated)]
+
+//! Memory allocation APIs
+
+use core::cmp;
+use core::fmt;
+use core::mem;
+use core::ptr::{self, NonNull};
+use core::usize;
+
+pub use core::alloc::{Layout, LayoutErr};
+
+fn new_layout_err() -> LayoutErr {
+    Layout::from_size_align(1, 3).unwrap_err()
+}
+
+pub fn handle_alloc_error(layout: Layout) -> ! {
+    panic!("encountered allocation error: {:?}", layout)
+}
+
+pub trait UnstableLayoutMethods {
+    fn padding_needed_for(&self, align: usize) -> usize;
+    fn repeat(&self, n: usize) -> Result<(Layout, usize), LayoutErr>;
+    fn array<T>(n: usize) -> Result<Layout, LayoutErr>;
+}
+
+impl UnstableLayoutMethods for Layout {
+    fn padding_needed_for(&self, align: usize) -> usize {
+        let len = self.size();
+
+        // Rounded up value is:
+        //   len_rounded_up = (len + align - 1) & !(align - 1);
+        // and then we return the padding difference: `len_rounded_up - len`.
+        //
+        // We use modular arithmetic throughout:
+        //
+        // 1. align is guaranteed to be > 0, so align - 1 is always
+        //    valid.
+        //
+        // 2. `len + align - 1` can overflow by at most `align - 1`,
+        //    so the &-mask with `!(align - 1)` will ensure that in the
+        //    case of overflow, `len_rounded_up` will itself be 0.
+        //    Thus the returned padding, when added to `len`, yields 0,
+        //    which trivially satisfies the alignment `align`.
+        //
+        // (Of course, attempts to allocate blocks of memory whose
+        // size and padding overflow in the above manner should cause
+        // the allocator to yield an error anyway.)
+
+        let len_rounded_up = len.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1);
+        len_rounded_up.wrapping_sub(len)
+    }
+
+    fn repeat(&self, n: usize) -> Result<(Layout, usize), LayoutErr> {
+        let padded_size = self
+            .size()
+            .checked_add(self.padding_needed_for(self.align()))
+            .ok_or_else(new_layout_err)?;
+        let alloc_size = padded_size.checked_mul(n).ok_or_else(new_layout_err)?;
+
+        unsafe {
+            // self.align is already known to be valid and alloc_size has been
+            // padded already.
+            Ok((
+                Layout::from_size_align_unchecked(alloc_size, self.align()),
+                padded_size,
+            ))
+        }
+    }
+
+    fn array<T>(n: usize) -> Result<Layout, LayoutErr> {
+        Layout::new::<T>().repeat(n).map(|(k, offs)| {
+            debug_assert!(offs == mem::size_of::<T>());
+            k
+        })
+    }
+}
+
+/// Represents the combination of a starting address and
+/// a total capacity of the returned block.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Debug)]
+pub struct Excess(pub NonNull<u8>, pub usize);
+
+fn size_align<T>() -> (usize, usize) {
+    (mem::size_of::<T>(), mem::align_of::<T>())
+}
+
+/// The `AllocErr` error indicates an allocation failure
+/// that may be due to resource exhaustion or to
+/// something wrong when combining the given input arguments with this
+/// allocator.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct AllocErr;
+
+// (we need this for downstream impl of trait Error)
+// #[unstable(feature = "allocator_api", issue = "32838")]
+impl fmt::Display for AllocErr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("memory allocation failed")
+    }
+}
+
+/// The `CannotReallocInPlace` error is used when `grow_in_place` or
+/// `shrink_in_place` were unable to reuse the given memory block for
+/// a requested layout.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct CannotReallocInPlace;
+
+// #[unstable(feature = "allocator_api", issue = "32838")]
+impl CannotReallocInPlace {
+    pub fn description(&self) -> &str {
+        "cannot reallocate allocator's memory in place"
+    }
+}
+
+// (we need this for downstream impl of trait Error)
+// #[unstable(feature = "allocator_api", issue = "32838")]
+impl fmt::Display for CannotReallocInPlace {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.description())
+    }
+}
+
+/// An implementation of `Alloc` can allocate, reallocate, and
+/// deallocate arbitrary blocks of data described via `Layout`.
+///
+/// Some of the methods require that a memory block be *currently
+/// allocated* via an allocator. This means that:
+///
+/// * the starting address for that memory block was previously
+///   returned by a previous call to an allocation method (`alloc`,
+///   `alloc_zeroed`, `alloc_excess`, `alloc_one`, `alloc_array`) or
+///   reallocation method (`realloc`, `realloc_excess`, or
+///   `realloc_array`), and
+///
+/// * the memory block has not been subsequently deallocated, where
+///   blocks are deallocated either by being passed to a deallocation
+///   method (`dealloc`, `dealloc_one`, `dealloc_array`) or by being
+///   passed to a reallocation method (see above) that returns `Ok`.
+///
+/// A note regarding zero-sized types and zero-sized layouts: many
+/// methods in the `Alloc` trait state that allocation requests
+/// must be non-zero size, or else undefined behavior can result.
+///
+/// * However, some higher-level allocation methods (`alloc_one`,
+///   `alloc_array`) are well-defined on zero-sized types and can
+///   optionally support them: it is left up to the implementor
+///   whether to return `Err`, or to return `Ok` with some pointer.
+///
+/// * If an `Alloc` implementation chooses to return `Ok` in this
+///   case (i.e. the pointer denotes a zero-sized inaccessible block)
+///   then that returned pointer must be considered "currently
+///   allocated". On such an allocator, *all* methods that take
+///   currently-allocated pointers as inputs must accept these
+///   zero-sized pointers, *without* causing undefined behavior.
+///
+/// * In other words, if a zero-sized pointer can flow out of an
+///   allocator, then that allocator must likewise accept that pointer
+///   flowing back into its deallocation and reallocation methods.
+///
+/// Some of the methods require that a layout *fit* a memory block.
+/// What it means for a layout to "fit" a memory block means (or
+/// equivalently, for a memory block to "fit" a layout) is that the
+/// following two conditions must hold:
+///
+/// 1. The block's starting address must be aligned to `layout.align()`.
+///
+/// 2. The block's size must fall in the range `[use_min, use_max]`, where:
+///
+///    * `use_min` is `self.usable_size(layout).0`, and
+///
+///    * `use_max` is the capacity that was (or would have been)
+///      returned when (if) the block was allocated via a call to
+///      `alloc_excess` or `realloc_excess`.
+///
+/// Note that:
+///
+///  * the size of the layout most recently used to allocate the block
+///    is guaranteed to be in the range `[use_min, use_max]`, and
+///
+///  * a lower-bound on `use_max` can be safely approximated by a call to
+///    `usable_size`.
+///
+///  * if a layout `k` fits a memory block (denoted by `ptr`)
+///    currently allocated via an allocator `a`, then it is legal to
+///    use that layout to deallocate it, i.e. `a.dealloc(ptr, k);`.
+///
+/// # Unsafety
+///
+/// The `Alloc` trait is an `unsafe` trait for a number of reasons, and
+/// implementors must ensure that they adhere to these contracts:
+///
+/// * Pointers returned from allocation functions must point to valid memory and
+///   retain their validity until at least the instance of `Alloc` is dropped
+///   itself.
+///
+/// * `Layout` queries and calculations in general must be correct. Callers of
+///   this trait are allowed to rely on the contracts defined on each method,
+///   and implementors must ensure such contracts remain true.
+///
+/// Note that this list may get tweaked over time as clarifications are made in
+/// the future.
+// #[unstable(feature = "allocator_api", issue = "32838")]
+pub unsafe trait Alloc {
+    // (Note: some existing allocators have unspecified but well-defined
+    // behavior in response to a zero size allocation request ;
+    // e.g. in C, `malloc` of 0 will either return a null pointer or a
+    // unique pointer, but will not have arbitrary undefined
+    // behavior.
+    // However in jemalloc for example,
+    // `mallocx(0)` is documented as undefined behavior.)
+
+    /// Returns a pointer meeting the size and alignment guarantees of
+    /// `layout`.
+    ///
+    /// If this method returns an `Ok(addr)`, then the `addr` returned
+    /// will be non-null address pointing to a block of storage
+    /// suitable for holding an instance of `layout`.
+    ///
+    /// The returned block of storage may or may not have its contents
+    /// initialized. (Extension subtraits might restrict this
+    /// behavior, e.g. to ensure initialization to particular sets of
+    /// bit patterns.)
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure that `layout` has non-zero size.
+    ///
+    /// (Extension subtraits might provide more specific bounds on
+    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// in response to a zero-size allocation request.)
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// Implementations are encouraged to return `Err` on memory
+    /// exhaustion rather than panicking or aborting, but this is not
+    /// a strict requirement. (Specifically: it is *legal* to
+    /// implement this trait atop an underlying native allocation
+    /// library that aborts on memory exhaustion.)
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr>;
+
+    /// Deallocate the memory referenced by `ptr`.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must denote a block of memory currently allocated via
+    ///   this allocator,
+    ///
+    /// * `layout` must *fit* that block of memory,
+    ///
+    /// * In addition to fitting the block of memory `layout`, the
+    ///   alignment of the `layout` must match the alignment used
+    ///   to allocate that block of memory.
+    unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout);
+
+    // == ALLOCATOR-SPECIFIC QUANTITIES AND LIMITS ==
+    // usable_size
+
+    /// Returns bounds on the guaranteed usable size of a successful
+    /// allocation created with the specified `layout`.
+    ///
+    /// In particular, if one has a memory block allocated via a given
+    /// allocator `a` and layout `k` where `a.usable_size(k)` returns
+    /// `(l, u)`, then one can pass that block to `a.dealloc()` with a
+    /// layout in the size range [l, u].
+    ///
+    /// (All implementors of `usable_size` must ensure that
+    /// `l <= k.size() <= u`)
+    ///
+    /// Both the lower- and upper-bounds (`l` and `u` respectively)
+    /// are provided, because an allocator based on size classes could
+    /// misbehave if one attempts to deallocate a block without
+    /// providing a correct value for its size (i.e., one within the
+    /// range `[l, u]`).
+    ///
+    /// Clients who wish to make use of excess capacity are encouraged
+    /// to use the `alloc_excess` and `realloc_excess` instead, as
+    /// this method is constrained to report conservative values that
+    /// serve as valid bounds for *all possible* allocation method
+    /// calls.
+    ///
+    /// However, for clients that do not wish to track the capacity
+    /// returned by `alloc_excess` locally, this method is likely to
+    /// produce useful results.
+    #[inline]
+    fn usable_size(&self, layout: &Layout) -> (usize, usize) {
+        (layout.size(), layout.size())
+    }
+
+    // == METHODS FOR MEMORY REUSE ==
+    // realloc. alloc_excess, realloc_excess
+
+    /// Returns a pointer suitable for holding data described by
+    /// a new layout with `layout`’s alignment and a size given
+    /// by `new_size`. To
+    /// accomplish this, this may extend or shrink the allocation
+    /// referenced by `ptr` to fit the new layout.
+    ///
+    /// If this returns `Ok`, then ownership of the memory block
+    /// referenced by `ptr` has been transferred to this
+    /// allocator. The memory may or may not have been freed, and
+    /// should be considered unusable (unless of course it was
+    /// transferred back to the caller again via the return value of
+    /// this method).
+    ///
+    /// If this method returns `Err`, then ownership of the memory
+    /// block has not been transferred to this allocator, and the
+    /// contents of the memory block are unaltered.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * `layout` must *fit* the `ptr` (see above). (The `new_size`
+    ///   argument need not fit it.)
+    ///
+    /// * `new_size` must be greater than zero.
+    ///
+    /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,
+    ///   must not overflow (i.e. the rounded value must be less than `usize::MAX`).
+    ///
+    /// (Extension subtraits might provide more specific bounds on
+    /// behavior, e.g. guarantee a sentinel address or a null pointer
+    /// in response to a zero-size allocation request.)
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err` only if the new layout
+    /// does not meet the allocator's size
+    /// and alignment constraints of the allocator, or if reallocation
+    /// otherwise fails.
+    ///
+    /// Implementations are encouraged to return `Err` on memory
+    /// exhaustion rather than panicking or aborting, but this is not
+    /// a strict requirement. (Specifically: it is *legal* to
+    /// implement this trait atop an underlying native allocation
+    /// library that aborts on memory exhaustion.)
+    ///
+    /// Clients wishing to abort computation in response to a
+    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn realloc(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<NonNull<u8>, AllocErr> {
+        let old_size = layout.size();
+
+        if new_size >= old_size {
+            if let Ok(()) = self.grow_in_place(ptr, layout, new_size) {
+                return Ok(ptr);
+            }
+        } else if new_size < old_size {
+            if let Ok(()) = self.shrink_in_place(ptr, layout, new_size) {
+                return Ok(ptr);
+            }
+        }
+
+        // otherwise, fall back on alloc + copy + dealloc.
+        let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
+        let result = self.alloc(new_layout);
+        if let Ok(new_ptr) = result {
+            ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), cmp::min(old_size, new_size));
+            self.dealloc(ptr, layout);
+        }
+        result
+    }
+
+    /// Behaves like `alloc`, but also ensures that the contents
+    /// are set to zero before being returned.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe for the same reasons that `alloc` is.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints, just as in `alloc`.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
+        let size = layout.size();
+        let p = self.alloc(layout);
+        if let Ok(p) = p {
+            ptr::write_bytes(p.as_ptr(), 0, size);
+        }
+        p
+    }
+
+    /// Behaves like `alloc`, but also returns the whole size of
+    /// the returned block. For some `layout` inputs, like arrays, this
+    /// may include extra storage usable for additional data.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe for the same reasons that `alloc` is.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints, just as in `alloc`.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
+        let usable_size = self.usable_size(&layout);
+        self.alloc(layout).map(|p| Excess(p, usable_size.1))
+    }
+
+    /// Behaves like `realloc`, but also returns the whole size of
+    /// the returned block. For some `layout` inputs, like arrays, this
+    /// may include extra storage usable for additional data.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe for the same reasons that `realloc` is.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `layout` does not meet allocator's size or alignment
+    /// constraints, just as in `realloc`.
+    ///
+    /// Clients wishing to abort computation in response to a
+    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn realloc_excess(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<Excess, AllocErr> {
+        let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
+        let usable_size = self.usable_size(&new_layout);
+        self.realloc(ptr, layout, new_size)
+            .map(|p| Excess(p, usable_size.1))
+    }
+
+    /// Attempts to extend the allocation referenced by `ptr` to fit `new_size`.
+    ///
+    /// If this returns `Ok`, then the allocator has asserted that the
+    /// memory block referenced by `ptr` now fits `new_size`, and thus can
+    /// be used to carry data of a layout of that size and same alignment as
+    /// `layout`. (The allocator is allowed to
+    /// expend effort to accomplish this, such as extending the memory block to
+    /// include successor blocks, or virtual memory tricks.)
+    ///
+    /// Regardless of what this method returns, ownership of the
+    /// memory block referenced by `ptr` has not been transferred, and
+    /// the contents of the memory block are unaltered.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * `layout` must *fit* the `ptr` (see above); note the
+    ///   `new_size` argument need not fit it,
+    ///
+    /// * `new_size` must not be less than `layout.size()`,
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(CannotReallocInPlace)` when the allocator is
+    /// unable to assert that the memory block referenced by `ptr`
+    /// could fit `layout`.
+    ///
+    /// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`
+    /// function; clients are expected either to be able to recover from
+    /// `grow_in_place` failures without aborting, or to fall back on
+    /// another reallocation method before resorting to an abort.
+    unsafe fn grow_in_place(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<(), CannotReallocInPlace> {
+        let _ = ptr; // this default implementation doesn't care about the actual address.
+        debug_assert!(new_size >= layout.size());
+        let (_l, u) = self.usable_size(&layout);
+        // _l <= layout.size()                       [guaranteed by usable_size()]
+        //       layout.size() <= new_layout.size()  [required by this method]
+        if new_size <= u {
+            Ok(())
+        } else {
+            Err(CannotReallocInPlace)
+        }
+    }
+
+    /// Attempts to shrink the allocation referenced by `ptr` to fit `new_size`.
+    ///
+    /// If this returns `Ok`, then the allocator has asserted that the
+    /// memory block referenced by `ptr` now fits `new_size`, and
+    /// thus can only be used to carry data of that smaller
+    /// layout. (The allocator is allowed to take advantage of this,
+    /// carving off portions of the block for reuse elsewhere.) The
+    /// truncated contents of the block within the smaller layout are
+    /// unaltered, and ownership of block has not been transferred.
+    ///
+    /// If this returns `Err`, then the memory block is considered to
+    /// still represent the original (larger) `layout`. None of the
+    /// block has been carved off for reuse elsewhere, ownership of
+    /// the memory block has not been transferred, and the contents of
+    /// the memory block are unaltered.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * `layout` must *fit* the `ptr` (see above); note the
+    ///   `new_size` argument need not fit it,
+    ///
+    /// * `new_size` must not be greater than `layout.size()`
+    ///   (and must be greater than zero),
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(CannotReallocInPlace)` when the allocator is
+    /// unable to assert that the memory block referenced by `ptr`
+    /// could fit `layout`.
+    ///
+    /// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`
+    /// function; clients are expected either to be able to recover from
+    /// `shrink_in_place` failures without aborting, or to fall back
+    /// on another reallocation method before resorting to an abort.
+    unsafe fn shrink_in_place(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<(), CannotReallocInPlace> {
+        let _ = ptr; // this default implementation doesn't care about the actual address.
+        debug_assert!(new_size <= layout.size());
+        let (l, _u) = self.usable_size(&layout);
+        //                      layout.size() <= _u  [guaranteed by usable_size()]
+        // new_layout.size() <= layout.size()        [required by this method]
+        if l <= new_size {
+            Ok(())
+        } else {
+            Err(CannotReallocInPlace)
+        }
+    }
+
+    // == COMMON USAGE PATTERNS ==
+    // alloc_one, dealloc_one, alloc_array, realloc_array. dealloc_array
+
+    /// Allocates a block suitable for holding an instance of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// The returned block is suitable for passing to the
+    /// `alloc`/`realloc` methods of this allocator.
+    ///
+    /// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
+    /// must be considered "currently allocated" and must be
+    /// acceptable input to methods such as `realloc` or `dealloc`,
+    /// *even if* `T` is a zero-sized type. In other words, if your
+    /// `Alloc` implementation overrides this method in a manner
+    /// that can return a zero-sized `ptr`, then all reallocation and
+    /// deallocation methods need to be similarly overridden to accept
+    /// such values as input.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `T` does not meet allocator's size or alignment constraints.
+    ///
+    /// For zero-sized `T`, may return either of `Ok` or `Err`, but
+    /// will *not* yield undefined behavior.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    fn alloc_one<T>(&mut self) -> Result<NonNull<T>, AllocErr>
+    where
+        Self: Sized,
+    {
+        let k = Layout::new::<T>();
+        if k.size() > 0 {
+            unsafe { self.alloc(k).map(|p| p.cast()) }
+        } else {
+            Err(AllocErr)
+        }
+    }
+
+    /// Deallocates a block suitable for holding an instance of `T`.
+    ///
+    /// The given block must have been produced by this allocator,
+    /// and must be suitable for storing a `T` (in terms of alignment
+    /// as well as minimum and maximum size); otherwise yields
+    /// undefined behavior.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure both:
+    ///
+    /// * `ptr` must denote a block of memory currently allocated via this allocator
+    ///
+    /// * the layout of `T` must *fit* that block of memory.
+    unsafe fn dealloc_one<T>(&mut self, ptr: NonNull<T>)
+    where
+        Self: Sized,
+    {
+        let k = Layout::new::<T>();
+        if k.size() > 0 {
+            self.dealloc(ptr.cast(), k);
+        }
+    }
+
+    /// Allocates a block suitable for holding `n` instances of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// The returned block is suitable for passing to the
+    /// `alloc`/`realloc` methods of this allocator.
+    ///
+    /// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
+    /// must be considered "currently allocated" and must be
+    /// acceptable input to methods such as `realloc` or `dealloc`,
+    /// *even if* `T` is a zero-sized type. In other words, if your
+    /// `Alloc` implementation overrides this method in a manner
+    /// that can return a zero-sized `ptr`, then all reallocation and
+    /// deallocation methods need to be similarly overridden to accept
+    /// such values as input.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `[T; n]` does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// For zero-sized `T` or `n == 0`, may return either of `Ok` or
+    /// `Err`, but will *not* yield undefined behavior.
+    ///
+    /// Always returns `Err` on arithmetic overflow.
+    ///
+    /// Clients wishing to abort computation in response to an
+    /// allocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    fn alloc_array<T>(&mut self, n: usize) -> Result<NonNull<T>, AllocErr>
+    where
+        Self: Sized,
+    {
+        match Layout::array::<T>(n) {
+            Ok(layout) if layout.size() > 0 => unsafe { self.alloc(layout).map(|p| p.cast()) },
+            _ => Err(AllocErr),
+        }
+    }
+
+    /// Reallocates a block previously suitable for holding `n_old`
+    /// instances of `T`, returning a block suitable for holding
+    /// `n_new` instances of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// The returned block is suitable for passing to the
+    /// `alloc`/`realloc` methods of this allocator.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure all of the following:
+    ///
+    /// * `ptr` must be currently allocated via this allocator,
+    ///
+    /// * the layout of `[T; n_old]` must *fit* that block of memory.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either memory is exhausted or
+    /// `[T; n_new]` does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// For zero-sized `T` or `n_new == 0`, may return either of `Ok` or
+    /// `Err`, but will *not* yield undefined behavior.
+    ///
+    /// Always returns `Err` on arithmetic overflow.
+    ///
+    /// Clients wishing to abort computation in response to a
+    /// reallocation error are encouraged to call the [`handle_alloc_error`] function,
+    /// rather than directly invoking `panic!` or similar.
+    ///
+    /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
+    unsafe fn realloc_array<T>(
+        &mut self,
+        ptr: NonNull<T>,
+        n_old: usize,
+        n_new: usize,
+    ) -> Result<NonNull<T>, AllocErr>
+    where
+        Self: Sized,
+    {
+        match (Layout::array::<T>(n_old), Layout::array::<T>(n_new)) {
+            (Ok(ref k_old), Ok(ref k_new)) if k_old.size() > 0 && k_new.size() > 0 => {
+                debug_assert!(k_old.align() == k_new.align());
+                self.realloc(ptr.cast(), k_old.clone(), k_new.size())
+                    .map(NonNull::cast)
+            }
+            _ => Err(AllocErr),
+        }
+    }
+
+    /// Deallocates a block suitable for holding `n` instances of `T`.
+    ///
+    /// Captures a common usage pattern for allocators.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because undefined behavior can result
+    /// if the caller does not ensure both:
+    ///
+    /// * `ptr` must denote a block of memory currently allocated via this allocator
+    ///
+    /// * the layout of `[T; n]` must *fit* that block of memory.
+    ///
+    /// # Errors
+    ///
+    /// Returning `Err` indicates that either `[T; n]` or the given
+    /// memory block does not meet allocator's size or alignment
+    /// constraints.
+    ///
+    /// Always returns `Err` on arithmetic overflow.
+    unsafe fn dealloc_array<T>(&mut self, ptr: NonNull<T>, n: usize) -> Result<(), AllocErr>
+    where
+        Self: Sized,
+    {
+        match Layout::array::<T>(n) {
+            Ok(k) if k.size() > 0 => {
+                self.dealloc(ptr.cast(), k);
+                Ok(())
+            }
+            _ => Err(AllocErr),
+        }
+    }
+}
diff --git a/third_party/rust/bumpalo/src/boxed.rs b/third_party/rust/bumpalo/src/boxed.rs
new file mode 100644
index 0000000000..cf9f4d6fee
--- /dev/null
+++ b/third_party/rust/bumpalo/src/boxed.rs
@@ -0,0 +1,684 @@
+//! A pointer type for bump allocation.
+//!
+//! [`Box<'a, T>`] provides the simplest form of
+//! bump allocation in `bumpalo`. Boxes provide ownership for this allocation, and
+//! drop their contents when they go out of scope.
+//!
+//! # Examples
+//!
+//! Move a value from the stack to the heap by creating a [`Box`]:
+//!
+//! ```
+//! use bumpalo::{Bump, boxed::Box};
+//!
+//! let b = Bump::new();
+//!
+//! let val: u8 = 5;
+//! let boxed: Box<u8> = Box::new_in(val, &b);
+//! ```
+//!
+//! Move a value from a [`Box`] back to the stack by [dereferencing]:
+//!
+//! ```
+//! use bumpalo::{Bump, boxed::Box};
+//!
+//! let b = Bump::new();
+//!
+//! let boxed: Box<u8> = Box::new_in(5, &b);
+//! let val: u8 = *boxed;
+//! ```
+//!
+//! Running [`Drop`] implementations on bump-allocated values:
+//!
+//! ```
+//! use bumpalo::{Bump, boxed::Box};
+//! use std::sync::atomic::{AtomicUsize, Ordering};
+//!
+//! static NUM_DROPPED: AtomicUsize = AtomicUsize::new(0);
+//!
+//! struct CountDrops;
+//!
+//! impl Drop for CountDrops {
+//!     fn drop(&mut self) {
+//!         NUM_DROPPED.fetch_add(1, Ordering::SeqCst);
+//!     }
+//! }
+//!
+//! // Create a new bump arena.
+//! let bump = Bump::new();
+//!
+//! // Create a `CountDrops` inside the bump arena.
+//! let mut c = Box::new_in(CountDrops, &bump);
+//!
+//! // No `CountDrops` have been dropped yet.
+//! assert_eq!(NUM_DROPPED.load(Ordering::SeqCst), 0);
+//!
+//! // Drop our `Box<CountDrops>`.
+//! drop(c);
+//!
+//! // Its `Drop` implementation was run, and so `NUM_DROPS` has been incremented.
+//! assert_eq!(NUM_DROPPED.load(Ordering::SeqCst), 1);
+//! ```
+//!
+//! Creating a recursive data structure:
+//!
+//! ```
+//! use bumpalo::{Bump, boxed::Box};
+//!
+//! let b = Bump::new();
+//!
+//! #[derive(Debug)]
+//! enum List<'a, T> {
+//!     Cons(T, Box<'a, List<'a, T>>),
+//!     Nil,
+//! }
+//!
+//! let list: List<i32> = List::Cons(1, Box::new_in(List::Cons(2, Box::new_in(List::Nil, &b)), &b));
+//! println!("{:?}", list);
+//! ```
+//!
+//! This will print `Cons(1, Cons(2, Nil))`.
+//!
+//! Recursive structures must be boxed, because if the definition of `Cons`
+//! looked like this:
+//!
+//! ```compile_fail,E0072
+//! # enum List<T> {
+//! Cons(T, List<T>),
+//! # }
+//! ```
+//!
+//! It wouldn't work. This is because the size of a `List` depends on how many
+//! elements are in the list, and so we don't know how much memory to allocate
+//! for a `Cons`. By introducing a [`Box<'a, T>`], which has a defined size, we know how
+//! big `Cons` needs to be.
+//!
+//! # Memory layout
+//!
+//! For non-zero-sized values, a [`Box`] will use the provided [`Bump`] allocator for
+//! its allocation. It is valid to convert both ways between a [`Box`] and a
+//! pointer allocated with the [`Bump`] allocator, given that the
+//! [`Layout`] used with the allocator is correct for the type. More precisely,
+//! a `value: *mut T` that has been allocated with the [`Bump`] allocator
+//! with `Layout::for_value(&*value)` may be converted into a box using
+//! [`Box::<T>::from_raw(value)`]. Conversely, the memory backing a `value: *mut
+//! T` obtained from [`Box::<T>::into_raw`] will be deallocated by the
+//! [`Bump`] allocator with [`Layout::for_value(&*value)`].
+//!
+//! Note that roundtrip `Box::from_raw(Box::into_raw(b))` looses the lifetime bound to the
+//! [`Bump`] immutable borrow which guarantees that the allocator will not be reset
+//! and memory will not be freed.
+//!
+//! [dereferencing]: https://doc.rust-lang.org/std/ops/trait.Deref.html
+//! [`Box`]: struct.Box.html
+//! [`Box<'a, T>`]: struct.Box.html
+//! [`Box::<T>::from_raw(value)`]: struct.Box.html#method.from_raw
+//! [`Box::<T>::into_raw`]: struct.Box.html#method.into_raw
+//! [`Bump`]: ../struct.Bump.html
+//! [`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html
+//! [`Layout`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html
+//! [`Layout::for_value(&*value)`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.for_value
+
+use {
+    crate::Bump,
+    {
+        core::{
+            any::Any,
+            borrow,
+            cmp::Ordering,
+            convert::TryFrom,
+            future::Future,
+            hash::{Hash, Hasher},
+            iter::FusedIterator,
+            mem,
+            ops::{Deref, DerefMut},
+            pin::Pin,
+            task::{Context, Poll},
+        },
+        core_alloc::fmt,
+    },
+};
+
+/// An owned pointer to a bump-allocated `T` value, that runs `Drop`
+/// implementations.
+///
+/// See the [module-level documentation][crate::boxed] for more details.
+#[repr(transparent)]
+pub struct Box<'a, T: ?Sized>(&'a mut T);
+
+impl<'a, T> Box<'a, T> {
+    /// Allocates memory on the heap and then places `x` into it.
+    ///
+    /// This doesn't actually allocate if `T` is zero-sized.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, boxed::Box};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let five = Box::new_in(5, &b);
+    /// ```
+    #[inline(always)]
+    pub fn new_in(x: T, a: &'a Bump) -> Box<'a, T> {
+        Box(a.alloc(x))
+    }
+
+    /// Constructs a new `Pin<Box<T>>`. If `T` does not implement `Unpin`, then
+    /// `x` will be pinned in memory and unable to be moved.
+    #[inline(always)]
+    pub fn pin_in(x: T, a: &'a Bump) -> Pin<Box<'a, T>> {
+        Box(a.alloc(x)).into()
+    }
+
+    /// Consumes the `Box`, returning the wrapped value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, boxed::Box};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let hello = Box::new_in("hello".to_owned(), &b);
+    /// assert_eq!(Box::into_inner(hello), "hello");
+    /// ```
+    pub fn into_inner(b: Box<'a, T>) -> T {
+        // `Box::into_raw` returns a pointer that is properly aligned and non-null.
+        // The underlying `Bump` only frees the memory, but won't call the destructor.
+        unsafe { core::ptr::read(Box::into_raw(b)) }
+    }
+}
+
+impl<'a, T: ?Sized> Box<'a, T> {
+    /// Constructs a box from a raw pointer.
+    ///
+    /// After calling this function, the raw pointer is owned by the
+    /// resulting `Box`. Specifically, the `Box` destructor will call
+    /// the destructor of `T` and free the allocated memory. For this
+    /// to be safe, the memory must have been allocated in accordance
+    /// with the memory layout used by `Box` .
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because improper use may lead to
+    /// memory problems. For example, a double-free may occur if the
+    /// function is called twice on the same raw pointer.
+    ///
+    /// # Examples
+    ///
+    /// Recreate a `Box` which was previously converted to a raw pointer
+    /// using [`Box::into_raw`]:
+    /// ```
+    /// use bumpalo::{Bump, boxed::Box};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let x = Box::new_in(5, &b);
+    /// let ptr = Box::into_raw(x);
+    /// let x = unsafe { Box::from_raw(ptr) }; // Note that new `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.
+    /// ```
+    /// Manually create a `Box` from scratch by using the bump allocator:
+    /// ```
+    /// use std::alloc::{alloc, Layout};
+    /// use bumpalo::{Bump, boxed::Box};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// unsafe {
+    ///     let ptr = b.alloc_layout(Layout::new::<i32>()).as_ptr() as *mut i32;
+    ///     *ptr = 5;
+    ///     let x = Box::from_raw(ptr); // Note that `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.
+    /// }
+    /// ```
+    #[inline]
+    pub unsafe fn from_raw(raw: *mut T) -> Self {
+        Box(&mut *raw)
+    }
+
+    /// Consumes the `Box`, returning a wrapped raw pointer.
+    ///
+    /// The pointer will be properly aligned and non-null.
+    ///
+    /// After calling this function, the caller is responsible for the
+    /// value previously managed by the `Box`. In particular, the
+    /// caller should properly destroy `T`. The easiest way to
+    /// do this is to convert the raw pointer back into a `Box` with the
+    /// [`Box::from_raw`] function, allowing the `Box` destructor to perform
+    /// the cleanup.
+    ///
+    /// Note: this is an associated function, which means that you have
+    /// to call it as `Box::into_raw(b)` instead of `b.into_raw()`. This
+    /// is so that there is no conflict with a method on the inner type.
+    ///
+    /// # Examples
+    ///
+    /// Converting the raw pointer back into a `Box` with [`Box::from_raw`]
+    /// for automatic cleanup:
+    /// ```
+    /// use bumpalo::{Bump, boxed::Box};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let x = Box::new_in(String::from("Hello"), &b);
+    /// let ptr = Box::into_raw(x);
+    /// let x = unsafe { Box::from_raw(ptr) }; // Note that new `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.
+    /// ```
+    /// Manual cleanup by explicitly running the destructor:
+    /// ```
+    /// use std::ptr;
+    /// use bumpalo::{Bump, boxed::Box};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut x = Box::new_in(String::from("Hello"), &b);
+    /// let p = Box::into_raw(x);
+    /// unsafe {
+    ///     ptr::drop_in_place(p);
+    /// }
+    /// ```
+    #[inline]
+    pub fn into_raw(b: Box<'a, T>) -> *mut T {
+        let ptr = b.0 as *mut T;
+        mem::forget(b);
+        ptr
+    }
+
+    /// Consumes and leaks the `Box`, returning a mutable reference,
+    /// `&'a mut T`. Note that the type `T` must outlive the chosen lifetime
+    /// `'a`. If the type has only static references, or none at all, then this
+    /// may be chosen to be `'static`.
+    ///
+    /// This function is mainly useful for data that lives for the remainder of
+    /// the program's life. Dropping the returned reference will cause a memory
+    /// leak. If this is not acceptable, the reference should first be wrapped
+    /// with the [`Box::from_raw`] function producing a `Box`. This `Box` can
+    /// then be dropped which will properly destroy `T` and release the
+    /// allocated memory.
+    ///
+    /// Note: this is an associated function, which means that you have
+    /// to call it as `Box::leak(b)` instead of `b.leak()`. This
+    /// is so that there is no conflict with a method on the inner type.
+    ///
+    /// # Examples
+    ///
+    /// Simple usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, boxed::Box};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let x = Box::new_in(41, &b);
+    /// let reference: &mut usize = Box::leak(x);
+    /// *reference += 1;
+    /// assert_eq!(*reference, 42);
+    /// ```
+    ///
+    ///```
+    /// # #[cfg(feature = "collections")]
+    /// # {
+    /// use bumpalo::{Bump, boxed::Box, vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let x = vec![in &b; 1, 2, 3].into_boxed_slice();
+    /// let reference = Box::leak(x);
+    /// reference[0] = 4;
+    /// assert_eq!(*reference, [4, 2, 3]);
+    /// # }
+    ///```
+    #[inline]
+    pub fn leak(b: Box<'a, T>) -> &'a mut T {
+        unsafe { &mut *Box::into_raw(b) }
+    }
+}
+
+impl<'a, T: ?Sized> Drop for Box<'a, T> {
+    fn drop(&mut self) {
+        unsafe {
+            // `Box` owns value of `T`, but not memory behind it.
+            core::ptr::drop_in_place(self.0);
+        }
+    }
+}
+
+impl<'a, T> Default for Box<'a, [T]> {
+    fn default() -> Box<'a, [T]> {
+        // It should be OK to `drop_in_place` empty slice of anything.
+        Box(&mut [])
+    }
+}
+
+impl<'a> Default for Box<'a, str> {
+    fn default() -> Box<'a, str> {
+        // Empty slice is valid string.
+        // It should be OK to `drop_in_place` empty str.
+        unsafe { Box::from_raw(Box::into_raw(Box::<[u8]>::default()) as *mut str) }
+    }
+}
+
+impl<'a, 'b, T: ?Sized + PartialEq> PartialEq<Box<'b, T>> for Box<'a, T> {
+    #[inline]
+    fn eq(&self, other: &Box<'b, T>) -> bool {
+        PartialEq::eq(&**self, &**other)
+    }
+    #[inline]
+    fn ne(&self, other: &Box<'b, T>) -> bool {
+        PartialEq::ne(&**self, &**other)
+    }
+}
+
+impl<'a, 'b, T: ?Sized + PartialOrd> PartialOrd<Box<'b, T>> for Box<'a, T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Box<'b, T>) -> Option<Ordering> {
+        PartialOrd::partial_cmp(&**self, &**other)
+    }
+    #[inline]
+    fn lt(&self, other: &Box<'b, T>) -> bool {
+        PartialOrd::lt(&**self, &**other)
+    }
+    #[inline]
+    fn le(&self, other: &Box<'b, T>) -> bool {
+        PartialOrd::le(&**self, &**other)
+    }
+    #[inline]
+    fn ge(&self, other: &Box<'b, T>) -> bool {
+        PartialOrd::ge(&**self, &**other)
+    }
+    #[inline]
+    fn gt(&self, other: &Box<'b, T>) -> bool {
+        PartialOrd::gt(&**self, &**other)
+    }
+}
+
+impl<'a, T: ?Sized + Ord> Ord for Box<'a, T> {
+    #[inline]
+    fn cmp(&self, other: &Box<'a, T>) -> Ordering {
+        Ord::cmp(&**self, &**other)
+    }
+}
+
+impl<'a, T: ?Sized + Eq> Eq for Box<'a, T> {}
+
+impl<'a, T: ?Sized + Hash> Hash for Box<'a, T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (**self).hash(state);
+    }
+}
+
+impl<'a, T: ?Sized + Hasher> Hasher for Box<'a, T> {
+    fn finish(&self) -> u64 {
+        (**self).finish()
+    }
+    fn write(&mut self, bytes: &[u8]) {
+        (**self).write(bytes)
+    }
+    fn write_u8(&mut self, i: u8) {
+        (**self).write_u8(i)
+    }
+    fn write_u16(&mut self, i: u16) {
+        (**self).write_u16(i)
+    }
+    fn write_u32(&mut self, i: u32) {
+        (**self).write_u32(i)
+    }
+    fn write_u64(&mut self, i: u64) {
+        (**self).write_u64(i)
+    }
+    fn write_u128(&mut self, i: u128) {
+        (**self).write_u128(i)
+    }
+    fn write_usize(&mut self, i: usize) {
+        (**self).write_usize(i)
+    }
+    fn write_i8(&mut self, i: i8) {
+        (**self).write_i8(i)
+    }
+    fn write_i16(&mut self, i: i16) {
+        (**self).write_i16(i)
+    }
+    fn write_i32(&mut self, i: i32) {
+        (**self).write_i32(i)
+    }
+    fn write_i64(&mut self, i: i64) {
+        (**self).write_i64(i)
+    }
+    fn write_i128(&mut self, i: i128) {
+        (**self).write_i128(i)
+    }
+    fn write_isize(&mut self, i: isize) {
+        (**self).write_isize(i)
+    }
+}
+
+impl<'a, T: ?Sized> From<Box<'a, T>> for Pin<Box<'a, T>> {
+    /// Converts a `Box<T>` into a `Pin<Box<T>>`.
+    ///
+    /// This conversion does not allocate on the heap and happens in place.
+    fn from(boxed: Box<'a, T>) -> Self {
+        // It's not possible to move or replace the insides of a `Pin<Box<T>>`
+        // when `T: !Unpin`,  so it's safe to pin it directly without any
+        // additional requirements.
+        unsafe { Pin::new_unchecked(boxed) }
+    }
+}
+
+impl<'a> Box<'a, dyn Any> {
+    #[inline]
+    /// Attempt to downcast the box to a concrete type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::any::Any;
+    ///
+    /// fn print_if_string(value: Box<dyn Any>) {
+    ///     if let Ok(string) = value.downcast::<String>() {
+    ///         println!("String ({}): {}", string.len(), string);
+    ///     }
+    /// }
+    ///
+    /// let my_string = "Hello World".to_string();
+    /// print_if_string(Box::new(my_string));
+    /// print_if_string(Box::new(0i8));
+    /// ```
+    pub fn downcast<T: Any>(self) -> Result<Box<'a, T>, Box<'a, dyn Any>> {
+        if self.is::<T>() {
+            unsafe {
+                let raw: *mut dyn Any = Box::into_raw(self);
+                Ok(Box::from_raw(raw as *mut T))
+            }
+        } else {
+            Err(self)
+        }
+    }
+}
+
+impl<'a> Box<'a, dyn Any + Send> {
+    #[inline]
+    /// Attempt to downcast the box to a concrete type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::any::Any;
+    ///
+    /// fn print_if_string(value: Box<dyn Any + Send>) {
+    ///     if let Ok(string) = value.downcast::<String>() {
+    ///         println!("String ({}): {}", string.len(), string);
+    ///     }
+    /// }
+    ///
+    /// let my_string = "Hello World".to_string();
+    /// print_if_string(Box::new(my_string));
+    /// print_if_string(Box::new(0i8));
+    /// ```
+    pub fn downcast<T: Any>(self) -> Result<Box<'a, T>, Box<'a, dyn Any + Send>> {
+        if self.is::<T>() {
+            unsafe {
+                let raw: *mut (dyn Any + Send) = Box::into_raw(self);
+                Ok(Box::from_raw(raw as *mut T))
+            }
+        } else {
+            Err(self)
+        }
+    }
+}
+
+impl<'a, T: fmt::Display + ?Sized> fmt::Display for Box<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: fmt::Debug + ?Sized> fmt::Debug for Box<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized> fmt::Pointer for Box<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // It's not possible to extract the inner Uniq directly from the Box,
+        // instead we cast it to a *const which aliases the Unique
+        let ptr: *const T = &**self;
+        fmt::Pointer::fmt(&ptr, f)
+    }
+}
+
+impl<'a, T: ?Sized> Deref for Box<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &*self.0
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for Box<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.0
+    }
+}
+
+impl<'a, I: Iterator + ?Sized> Iterator for Box<'a, I> {
+    type Item = I::Item;
+    fn next(&mut self) -> Option<I::Item> {
+        (**self).next()
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (**self).size_hint()
+    }
+    fn nth(&mut self, n: usize) -> Option<I::Item> {
+        (**self).nth(n)
+    }
+    fn last(self) -> Option<I::Item> {
+        #[inline]
+        fn some<T>(_: Option<T>, x: T) -> Option<T> {
+            Some(x)
+        }
+        self.fold(None, some)
+    }
+}
+
+impl<'a, I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<'a, I> {
+    fn next_back(&mut self) -> Option<I::Item> {
+        (**self).next_back()
+    }
+    fn nth_back(&mut self, n: usize) -> Option<I::Item> {
+        (**self).nth_back(n)
+    }
+}
+impl<'a, I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<'a, I> {
+    fn len(&self) -> usize {
+        (**self).len()
+    }
+}
+
+impl<'a, I: FusedIterator + ?Sized> FusedIterator for Box<'a, I> {}
+
+#[cfg(feature = "collections")]
+impl<'a, A> Box<'a, [A]> {
+    /// Creates a value from an iterator.
+    /// This method is an adapted version of [`FromIterator::from_iter`][from_iter].
+    /// It cannot be made as that trait implementation given different signature.
+    ///
+    /// [from_iter]: https://doc.rust-lang.org/std/iter/trait.FromIterator.html#tymethod.from_iter
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    /// ```
+    /// use bumpalo::{Bump, boxed::Box, vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let five_fives = std::iter::repeat(5).take(5);
+    /// let slice = Box::from_iter_in(five_fives, &b);
+    /// assert_eq!(vec![in &b; 5, 5, 5, 5, 5], &*slice);
+    /// ```
+    pub fn from_iter_in<T: IntoIterator<Item = A>>(iter: T, a: &'a Bump) -> Self {
+        use crate::collections::Vec;
+        let mut vec = Vec::new_in(a);
+        vec.extend(iter);
+        vec.into_boxed_slice()
+    }
+}
+
+impl<'a, T: ?Sized> borrow::Borrow<T> for Box<'a, T> {
+    fn borrow(&self) -> &T {
+        &**self
+    }
+}
+
+impl<'a, T: ?Sized> borrow::BorrowMut<T> for Box<'a, T> {
+    fn borrow_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+impl<'a, T: ?Sized> AsRef<T> for Box<'a, T> {
+    fn as_ref(&self) -> &T {
+        &**self
+    }
+}
+
+impl<'a, T: ?Sized> AsMut<T> for Box<'a, T> {
+    fn as_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+impl<'a, T: ?Sized> Unpin for Box<'a, T> {}
+
+impl<'a, F: ?Sized + Future + Unpin> Future for Box<'a, F> {
+    type Output = F::Output;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        F::poll(Pin::new(&mut *self), cx)
+    }
+}
+
+/// This impl replaces unsize coercion.
+impl<'a, T, const N: usize> From<Box<'a, [T; N]>> for Box<'a, [T]> {
+    fn from(mut arr: Box<'a, [T; N]>) -> Box<'a, [T]> {
+        let ptr = core::ptr::slice_from_raw_parts_mut(arr.as_mut_ptr(), N);
+        mem::forget(arr);
+        unsafe { Box::from_raw(ptr) }
+    }
+}
+
+/// This impl replaces unsize coercion.
+impl<'a, T, const N: usize> TryFrom<Box<'a, [T]>> for Box<'a, [T; N]> {
+    type Error = Box<'a, [T]>;
+    fn try_from(mut slice: Box<'a, [T]>) -> Result<Box<'a, [T; N]>, Box<'a, [T]>> {
+        if slice.len() == N {
+            let ptr = slice.as_mut_ptr() as *mut [T; N];
+            mem::forget(slice);
+            Ok(unsafe { Box::from_raw(ptr) })
+        } else {
+            Err(slice)
+        }
+    }
+}
diff --git a/third_party/rust/bumpalo/src/collections/collect_in.rs b/third_party/rust/bumpalo/src/collections/collect_in.rs
new file mode 100644
index 0000000000..3e1adeaeaa
--- /dev/null
+++ b/third_party/rust/bumpalo/src/collections/collect_in.rs
@@ -0,0 +1,152 @@
+#[cfg(feature = "boxed")]
+use crate::boxed::Box;
+use crate::collections::{String, Vec};
+use crate::Bump;
+
+/// A trait for types that support being constructed from an iterator, parameterized by an allocator.
+pub trait FromIteratorIn<A> {
+    /// The allocator type
+    type Alloc;
+
+    /// Similar to [`FromIterator::from_iter`][from_iter], but with a given allocator.
+    ///
+    /// [from_iter]: https://doc.rust-lang.org/std/iter/trait.FromIterator.html#tymethod.from_iter
+    ///
+    /// ```
+    /// # use bumpalo::collections::{FromIteratorIn, Vec};
+    /// # use bumpalo::Bump;
+    /// #
+    /// let five_fives = std::iter::repeat(5).take(5);
+    /// let bump = Bump::new();
+    ///
+    /// let v = Vec::from_iter_in(five_fives, &bump);
+    ///
+    /// assert_eq!(v, [5, 5, 5, 5, 5]);
+    /// ```
+    fn from_iter_in<I>(iter: I, alloc: Self::Alloc) -> Self
+    where
+        I: IntoIterator<Item = A>;
+}
+
+#[cfg(feature = "boxed")]
+impl<'bump, T> FromIteratorIn<T> for Box<'bump, [T]> {
+    type Alloc = &'bump Bump;
+
+    fn from_iter_in<I>(iter: I, alloc: Self::Alloc) -> Self
+    where
+        I: IntoIterator<Item = T>,
+    {
+        Box::from_iter_in(iter, alloc)
+    }
+}
+
+impl<'bump, T> FromIteratorIn<T> for Vec<'bump, T> {
+    type Alloc = &'bump Bump;
+
+    fn from_iter_in<I>(iter: I, alloc: Self::Alloc) -> Self
+    where
+        I: IntoIterator<Item = T>,
+    {
+        Vec::from_iter_in(iter, alloc)
+    }
+}
+
+impl<T, V: FromIteratorIn<T>> FromIteratorIn<Option<T>> for Option<V> {
+    type Alloc = V::Alloc;
+    fn from_iter_in<I>(iter: I, alloc: Self::Alloc) -> Self
+    where
+        I: IntoIterator<Item = Option<T>>,
+    {
+        iter.into_iter()
+            .map(|x| x.ok_or(()))
+            .collect_in::<Result<_, _>>(alloc)
+            .ok()
+    }
+}
+
+impl<T, E, V: FromIteratorIn<T>> FromIteratorIn<Result<T, E>> for Result<V, E> {
+    type Alloc = V::Alloc;
+    /// Takes each element in the `Iterator`: if it is an `Err`, no further
+    /// elements are taken, and the `Err` is returned. Should no `Err` occur, a
+    /// container with the values of each `Result` is returned.
+    ///
+    /// Here is an example which increments every integer in a vector,
+    /// checking for overflow:
+    ///
+    /// ```
+    /// # use bumpalo::collections::{FromIteratorIn, CollectIn, Vec, String};
+    /// # use bumpalo::Bump;
+    /// #
+    /// let bump = Bump::new();
+    ///
+    /// let v = vec![1, 2, u32::MAX];
+    /// let res: Result<Vec<u32>, &'static str> = v.iter().take(2).map(|x: &u32|
+    ///     x.checked_add(1).ok_or("Overflow!")
+    /// ).collect_in(&bump);
+    /// assert_eq!(res, Ok(bumpalo::vec![in &bump; 2, 3]));
+    ///
+    /// let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
+    ///     x.checked_add(1).ok_or("Overflow!")
+    /// ).collect_in(&bump);
+    /// assert_eq!(res, Err("Overflow!"));
+    /// ```
+    fn from_iter_in<I>(iter: I, alloc: Self::Alloc) -> Self
+    where
+        I: IntoIterator<Item = Result<T, E>>,
+    {
+        let mut iter = iter.into_iter();
+        let mut error = None;
+        let container = core::iter::from_fn(|| match iter.next() {
+            Some(Ok(x)) => Some(x),
+            Some(Err(e)) => {
+                error = Some(e);
+                None
+            }
+            None => None,
+        })
+        .collect_in(alloc);
+
+        match error {
+            Some(e) => Err(e),
+            None => Ok(container),
+        }
+    }
+}
+
+impl<'bump> FromIteratorIn<char> for String<'bump> {
+    type Alloc = &'bump Bump;
+
+    fn from_iter_in<I>(iter: I, alloc: Self::Alloc) -> Self
+    where
+        I: IntoIterator<Item = char>,
+    {
+        String::from_iter_in(iter, alloc)
+    }
+}
+
+/// Extension trait for iterators, in order to allow allocator-parameterized collections to be constructed more easily.
+pub trait CollectIn: Iterator + Sized {
+    /// Collect all items from an iterator, into a collection parameterized by an allocator.
+    /// Similar to [`Iterator::collect`][collect].
+    ///
+    /// [collect]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.collect
+    ///
+    /// ```
+    /// # use bumpalo::collections::{FromIteratorIn, CollectIn, Vec, String};
+    /// # use bumpalo::Bump;
+    /// #
+    /// let bump = Bump::new();
+    ///
+    /// let str = "hello, world!".to_owned();
+    /// let bump_str: String = str.chars().collect_in(&bump);
+    /// assert_eq!(&bump_str, &str);
+    ///
+    /// let nums: Vec<i32> = (0..=3).collect_in::<Vec<_>>(&bump);
+    /// assert_eq!(&nums, &[0,1,2,3]);
+    /// ```
+    fn collect_in<C: FromIteratorIn<Self::Item>>(self, alloc: C::Alloc) -> C {
+        C::from_iter_in(self, alloc)
+    }
+}
+
+impl<I: Iterator> CollectIn for I {}
diff --git a/third_party/rust/bumpalo/src/collections/mod.rs b/third_party/rust/bumpalo/src/collections/mod.rs
new file mode 100644
index 0000000000..218636c320
--- /dev/null
+++ b/third_party/rust/bumpalo/src/collections/mod.rs
@@ -0,0 +1,93 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Collection types that allocate inside a [`Bump`] arena.
+//!
+//! [`Bump`]: ../struct.Bump.html
+
+#![allow(deprecated)]
+
+mod raw_vec;
+
+pub mod vec;
+pub use self::vec::Vec;
+
+mod str;
+pub mod string;
+pub use self::string::String;
+
+mod collect_in;
+pub use collect_in::{CollectIn, FromIteratorIn};
+
+// pub mod binary_heap;
+// mod btree;
+// pub mod linked_list;
+// pub mod vec_deque;
+
+// pub mod btree_map {
+//     //! A map based on a B-Tree.
+//     pub use super::btree::map::*;
+// }
+
+// pub mod btree_set {
+//     //! A set based on a B-Tree.
+//     pub use super::btree::set::*;
+// }
+
+// #[doc(no_inline)]
+// pub use self::binary_heap::BinaryHeap;
+
+// #[doc(no_inline)]
+// pub use self::btree_map::BTreeMap;
+
+// #[doc(no_inline)]
+// pub use self::btree_set::BTreeSet;
+
+// #[doc(no_inline)]
+// pub use self::linked_list::LinkedList;
+
+// #[doc(no_inline)]
+// pub use self::vec_deque::VecDeque;
+
+use crate::alloc::{AllocErr, LayoutErr};
+
+/// Augments `AllocErr` with a `CapacityOverflow` variant.
+#[derive(Clone, PartialEq, Eq, Debug)]
+// #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
+pub enum CollectionAllocErr {
+    /// Error due to the computed capacity exceeding the collection's maximum
+    /// (usually `isize::MAX` bytes).
+    CapacityOverflow,
+    /// Error due to the allocator (see the documentation for the [`AllocErr`] type).
+    AllocErr,
+}
+
+// #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
+impl From<AllocErr> for CollectionAllocErr {
+    #[inline]
+    fn from(AllocErr: AllocErr) -> Self {
+        CollectionAllocErr::AllocErr
+    }
+}
+
+// #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
+impl From<LayoutErr> for CollectionAllocErr {
+    #[inline]
+    fn from(_: LayoutErr) -> Self {
+        CollectionAllocErr::CapacityOverflow
+    }
+}
+
+// /// An intermediate trait for specialization of `Extend`.
+// #[doc(hidden)]
+// trait SpecExtend<I: IntoIterator> {
+//     /// Extends `self` with the contents of the given iterator.
+//     fn spec_extend(&mut self, iter: I);
+// }
diff --git a/third_party/rust/bumpalo/src/collections/raw_vec.rs b/third_party/rust/bumpalo/src/collections/raw_vec.rs
new file mode 100644
index 0000000000..ac3bd0758c
--- /dev/null
+++ b/third_party/rust/bumpalo/src/collections/raw_vec.rs
@@ -0,0 +1,730 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(unstable_name_collisions)]
+#![allow(dead_code)]
+
+use crate::Bump;
+
+use core::cmp;
+use core::mem;
+use core::ptr::{self, NonNull};
+
+use crate::alloc::{handle_alloc_error, Alloc, Layout, UnstableLayoutMethods};
+use crate::collections::CollectionAllocErr;
+use crate::collections::CollectionAllocErr::*;
+// use boxed::Box;
+
+/// A low-level utility for more ergonomically allocating, reallocating, and deallocating
+/// a buffer of memory on the heap without having to worry about all the corner cases
+/// involved. This type is excellent for building your own data structures like Vec and VecDeque.
+/// In particular:
+///
+/// * Produces Unique::empty() on zero-sized types
+/// * Produces Unique::empty() on zero-length allocations
+/// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics)
+/// * Guards against 32-bit systems allocating more than isize::MAX bytes
+/// * Guards against overflowing your length
+/// * Aborts on OOM
+/// * Avoids freeing Unique::empty()
+/// * Contains a ptr::Unique and thus endows the user with all related benefits
+///
+/// This type does not in anyway inspect the memory that it manages. When dropped it *will*
+/// free its memory, but it *won't* try to Drop its contents. It is up to the user of RawVec
+/// to handle the actual things *stored* inside of a RawVec.
+///
+/// Note that a RawVec always forces its capacity to be usize::MAX for zero-sized types.
+/// This enables you to use capacity growing logic catch the overflows in your length
+/// that might occur with zero-sized types.
+///
+/// However this means that you need to be careful when round-tripping this type
+/// with a `Box<[T]>`: `cap()` won't yield the len. However `with_capacity`,
+/// `shrink_to_fit`, and `from_box` will actually set RawVec's private capacity
+/// field. This allows zero-sized types to not be special-cased by consumers of
+/// this type.
+#[allow(missing_debug_implementations)]
+pub struct RawVec<'a, T> {
+    ptr: NonNull<T>,
+    cap: usize,
+    a: &'a Bump,
+}
+
+impl<'a, T> RawVec<'a, T> {
+    /// Like `new` but parameterized over the choice of allocator for
+    /// the returned RawVec.
+    pub fn new_in(a: &'a Bump) -> Self {
+        // `cap: 0` means "unallocated". zero-sized types are ignored.
+        RawVec {
+            ptr: NonNull::dangling(),
+            cap: 0,
+            a,
+        }
+    }
+
+    /// Like `with_capacity` but parameterized over the choice of
+    /// allocator for the returned RawVec.
+    #[inline]
+    pub fn with_capacity_in(cap: usize, a: &'a Bump) -> Self {
+        RawVec::allocate_in(cap, false, a)
+    }
+
+    /// Like `with_capacity_zeroed` but parameterized over the choice
+    /// of allocator for the returned RawVec.
+    #[inline]
+    pub fn with_capacity_zeroed_in(cap: usize, a: &'a Bump) -> Self {
+        RawVec::allocate_in(cap, true, a)
+    }
+
+    fn allocate_in(cap: usize, zeroed: bool, mut a: &'a Bump) -> Self {
+        unsafe {
+            let elem_size = mem::size_of::<T>();
+
+            let alloc_size = cap
+                .checked_mul(elem_size)
+                .unwrap_or_else(|| capacity_overflow());
+            alloc_guard(alloc_size).unwrap_or_else(|_| capacity_overflow());
+
+            // handles ZSTs and `cap = 0` alike
+            let ptr = if alloc_size == 0 {
+                NonNull::<T>::dangling()
+            } else {
+                let align = mem::align_of::<T>();
+                let layout = Layout::from_size_align(alloc_size, align).unwrap();
+                let result = if zeroed {
+                    a.alloc_zeroed(layout)
+                } else {
+                    Alloc::alloc(&mut a, layout)
+                };
+                match result {
+                    Ok(ptr) => ptr.cast(),
+                    Err(_) => handle_alloc_error(layout),
+                }
+            };
+
+            RawVec { ptr, cap, a }
+        }
+    }
+}
+
+impl<'a, T> RawVec<'a, T> {
+    /// Reconstitutes a RawVec from a pointer, capacity, and allocator.
+    ///
+    /// # Undefined Behavior
+    ///
+    /// The ptr must be allocated (via the given allocator `a`), and with the given capacity. The
+    /// capacity cannot exceed `isize::MAX` (only a concern on 32-bit systems).
+    /// If the ptr and capacity come from a RawVec created via `a`, then this is guaranteed.
+    pub unsafe fn from_raw_parts_in(ptr: *mut T, cap: usize, a: &'a Bump) -> Self {
+        RawVec {
+            ptr: NonNull::new_unchecked(ptr),
+            cap,
+            a,
+        }
+    }
+}
+
+impl<'a, T> RawVec<'a, T> {
+    /// Gets a raw pointer to the start of the allocation. Note that this is
+    /// Unique::empty() if `cap = 0` or T is zero-sized. In the former case, you must
+    /// be careful.
+    pub fn ptr(&self) -> *mut T {
+        self.ptr.as_ptr()
+    }
+
+    /// Gets the capacity of the allocation.
+    ///
+    /// This will always be `usize::MAX` if `T` is zero-sized.
+    #[inline(always)]
+    pub fn cap(&self) -> usize {
+        if mem::size_of::<T>() == 0 {
+            !0
+        } else {
+            self.cap
+        }
+    }
+
+    /// Returns a shared reference to the allocator backing this RawVec.
+    pub fn bump(&self) -> &'a Bump {
+        self.a
+    }
+
+    fn current_layout(&self) -> Option<Layout> {
+        if self.cap == 0 {
+            None
+        } else {
+            // We have an allocated chunk of memory, so we can bypass runtime
+            // checks to get our current layout.
+            unsafe {
+                let align = mem::align_of::<T>();
+                let size = mem::size_of::<T>() * self.cap;
+                Some(Layout::from_size_align_unchecked(size, align))
+            }
+        }
+    }
+
+    /// Doubles the size of the type's backing allocation. This is common enough
+    /// to want to do that it's easiest to just have a dedicated method. Slightly
+    /// more efficient logic can be provided for this than the general case.
+    ///
+    /// This function is ideal for when pushing elements one-at-a-time because
+    /// you don't need to incur the costs of the more general computations
+    /// reserve needs to do to guard against overflow. You do however need to
+    /// manually check if your `len == cap`.
+    ///
+    /// # Panics
+    ///
+    /// * Panics if T is zero-sized on the assumption that you managed to exhaust
+    ///   all `usize::MAX` slots in your imaginary buffer.
+    /// * Panics on 32-bit platforms if the requested capacity exceeds
+    ///   `isize::MAX` bytes.
+    ///
+    /// # Aborts
+    ///
+    /// Aborts on OOM
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// # #![feature(alloc, raw_vec_internals)]
+    /// # extern crate alloc;
+    /// # use std::ptr;
+    /// # use alloc::raw_vec::RawVec;
+    /// struct MyVec<T> {
+    ///     buf: RawVec<T>,
+    ///     len: usize,
+    /// }
+    ///
+    /// impl<T> MyVec<T> {
+    ///     pub fn push(&mut self, elem: T) {
+    ///         if self.len == self.buf.cap() { self.buf.double(); }
+    ///         // double would have aborted or panicked if the len exceeded
+    ///         // `isize::MAX` so this is safe to do unchecked now.
+    ///         unsafe {
+    ///             ptr::write(self.buf.ptr().add(self.len), elem);
+    ///         }
+    ///         self.len += 1;
+    ///     }
+    /// }
+    /// # fn main() {
+    /// #   let mut vec = MyVec { buf: RawVec::new(), len: 0 };
+    /// #   vec.push(1);
+    /// # }
+    /// ```
+    #[inline(never)]
+    #[cold]
+    pub fn double(&mut self) {
+        unsafe {
+            let elem_size = mem::size_of::<T>();
+
+            // since we set the capacity to usize::MAX when elem_size is
+            // 0, getting to here necessarily means the RawVec is overfull.
+            assert!(elem_size != 0, "capacity overflow");
+
+            let (new_cap, uniq) = match self.current_layout() {
+                Some(cur) => {
+                    // Since we guarantee that we never allocate more than
+                    // isize::MAX bytes, `elem_size * self.cap <= isize::MAX` as
+                    // a precondition, so this can't overflow. Additionally the
+                    // alignment will never be too large as to "not be
+                    // satisfiable", so `Layout::from_size_align` will always
+                    // return `Some`.
+                    //
+                    // tl;dr; we bypass runtime checks due to dynamic assertions
+                    // in this module, allowing us to use
+                    // `from_size_align_unchecked`.
+                    let new_cap = 2 * self.cap;
+                    let new_size = new_cap * elem_size;
+                    alloc_guard(new_size).unwrap_or_else(|_| capacity_overflow());
+                    let ptr_res = self.a.realloc(self.ptr.cast(), cur, new_size);
+                    match ptr_res {
+                        Ok(ptr) => (new_cap, ptr.cast()),
+                        Err(_) => handle_alloc_error(Layout::from_size_align_unchecked(
+                            new_size,
+                            cur.align(),
+                        )),
+                    }
+                }
+                None => {
+                    // skip to 4 because tiny Vec's are dumb; but not if that
+                    // would cause overflow
+                    let new_cap = if elem_size > (!0) / 8 { 1 } else { 4 };
+                    match self.a.alloc_array::<T>(new_cap) {
+                        Ok(ptr) => (new_cap, ptr),
+                        Err(_) => handle_alloc_error(Layout::array::<T>(new_cap).unwrap()),
+                    }
+                }
+            };
+            self.ptr = uniq;
+            self.cap = new_cap;
+        }
+    }
+
+    /// Attempts to double the size of the type's backing allocation in place. This is common
+    /// enough to want to do that it's easiest to just have a dedicated method. Slightly
+    /// more efficient logic can be provided for this than the general case.
+    ///
+    /// Returns true if the reallocation attempt has succeeded, or false otherwise.
+    ///
+    /// # Panics
+    ///
+    /// * Panics if T is zero-sized on the assumption that you managed to exhaust
+    ///   all `usize::MAX` slots in your imaginary buffer.
+    /// * Panics on 32-bit platforms if the requested capacity exceeds
+    ///   `isize::MAX` bytes.
+    #[inline(never)]
+    #[cold]
+    pub fn double_in_place(&mut self) -> bool {
+        unsafe {
+            let elem_size = mem::size_of::<T>();
+            let old_layout = match self.current_layout() {
+                Some(layout) => layout,
+                None => return false, // nothing to double
+            };
+
+            // since we set the capacity to usize::MAX when elem_size is
+            // 0, getting to here necessarily means the RawVec is overfull.
+            assert!(elem_size != 0, "capacity overflow");
+
+            // Since we guarantee that we never allocate more than isize::MAX
+            // bytes, `elem_size * self.cap <= isize::MAX` as a precondition, so
+            // this can't overflow.
+            //
+            // Similarly like with `double` above we can go straight to
+            // `Layout::from_size_align_unchecked` as we know this won't
+            // overflow and the alignment is sufficiently small.
+            let new_cap = 2 * self.cap;
+            let new_size = new_cap * elem_size;
+            alloc_guard(new_size).unwrap_or_else(|_| capacity_overflow());
+            match self.a.grow_in_place(self.ptr.cast(), old_layout, new_size) {
+                Ok(_) => {
+                    // We can't directly divide `size`.
+                    self.cap = new_cap;
+                    true
+                }
+                Err(_) => false,
+            }
+        }
+    }
+
+    /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
+    pub fn try_reserve_exact(
+        &mut self,
+        used_cap: usize,
+        needed_extra_cap: usize,
+    ) -> Result<(), CollectionAllocErr> {
+        self.reserve_internal(used_cap, needed_extra_cap, Fallible, Exact)
+    }
+
+    /// Ensures that the buffer contains at least enough space to hold
+    /// `used_cap + needed_extra_cap` elements. If it doesn't already,
+    /// will reallocate the minimum possible amount of memory necessary.
+    /// Generally this will be exactly the amount of memory necessary,
+    /// but in principle the allocator is free to give back more than
+    /// we asked for.
+    ///
+    /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
+    /// the requested space. This is not really unsafe, but the unsafe
+    /// code *you* write that relies on the behavior of this function may break.
+    ///
+    /// # Panics
+    ///
+    /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
+    /// * Panics on 32-bit platforms if the requested capacity exceeds
+    ///   `isize::MAX` bytes.
+    ///
+    /// # Aborts
+    ///
+    /// Aborts on OOM
+    pub fn reserve_exact(&mut self, used_cap: usize, needed_extra_cap: usize) {
+        match self.reserve_internal(used_cap, needed_extra_cap, Infallible, Exact) {
+            Err(CapacityOverflow) => capacity_overflow(),
+            Err(AllocErr) => unreachable!(),
+            Ok(()) => { /* yay */ }
+        }
+    }
+
+    /// Calculates the buffer's new size given that it'll hold `used_cap +
+    /// needed_extra_cap` elements. This logic is used in amortized reserve methods.
+    /// Returns `(new_capacity, new_alloc_size)`.
+    fn amortized_new_size(
+        &self,
+        used_cap: usize,
+        needed_extra_cap: usize,
+    ) -> Result<usize, CollectionAllocErr> {
+        // Nothing we can really do about these checks :(
+        let required_cap = used_cap
+            .checked_add(needed_extra_cap)
+            .ok_or(CapacityOverflow)?;
+        // Cannot overflow, because `cap <= isize::MAX`, and type of `cap` is `usize`.
+        let double_cap = self.cap * 2;
+        // `double_cap` guarantees exponential growth.
+        Ok(cmp::max(double_cap, required_cap))
+    }
+
+    /// The same as `reserve`, but returns on errors instead of panicking or aborting.
+    pub fn try_reserve(
+        &mut self,
+        used_cap: usize,
+        needed_extra_cap: usize,
+    ) -> Result<(), CollectionAllocErr> {
+        self.reserve_internal(used_cap, needed_extra_cap, Fallible, Amortized)
+    }
+
+    /// Ensures that the buffer contains at least enough space to hold
+    /// `used_cap + needed_extra_cap` elements. If it doesn't already have
+    /// enough capacity, will reallocate enough space plus comfortable slack
+    /// space to get amortized `O(1)` behavior. Will limit this behavior
+    /// if it would needlessly cause itself to panic.
+    ///
+    /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
+    /// the requested space. This is not really unsafe, but the unsafe
+    /// code *you* write that relies on the behavior of this function may break.
+    ///
+    /// This is ideal for implementing a bulk-push operation like `extend`.
+    ///
+    /// # Panics
+    ///
+    /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
+    /// * Panics on 32-bit platforms if the requested capacity exceeds
+    ///   `isize::MAX` bytes.
+    ///
+    /// # Aborts
+    ///
+    /// Aborts on OOM
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// # #![feature(alloc, raw_vec_internals)]
+    /// # extern crate alloc;
+    /// # use std::ptr;
+    /// # use alloc::raw_vec::RawVec;
+    /// struct MyVec<T> {
+    ///     buf: RawVec<T>,
+    ///     len: usize,
+    /// }
+    ///
+    /// impl<T: Clone> MyVec<T> {
+    ///     pub fn push_all(&mut self, elems: &[T]) {
+    ///         self.buf.reserve(self.len, elems.len());
+    ///         // reserve would have aborted or panicked if the len exceeded
+    ///         // `isize::MAX` so this is safe to do unchecked now.
+    ///         for x in elems {
+    ///             unsafe {
+    ///                 ptr::write(self.buf.ptr().add(self.len), x.clone());
+    ///             }
+    ///             self.len += 1;
+    ///         }
+    ///     }
+    /// }
+    /// # fn main() {
+    /// #   let mut vector = MyVec { buf: RawVec::new(), len: 0 };
+    /// #   vector.push_all(&[1, 3, 5, 7, 9]);
+    /// # }
+    /// ```
+    pub fn reserve(&mut self, used_cap: usize, needed_extra_cap: usize) {
+        match self.reserve_internal(used_cap, needed_extra_cap, Infallible, Amortized) {
+            Err(CapacityOverflow) => capacity_overflow(),
+            Err(AllocErr) => unreachable!(),
+            Ok(()) => { /* yay */ }
+        }
+    }
+    /// Attempts to ensure that the buffer contains at least enough space to hold
+    /// `used_cap + needed_extra_cap` elements. If it doesn't already have
+    /// enough capacity, will reallocate in place enough space plus comfortable slack
+    /// space to get amortized `O(1)` behavior. Will limit this behaviour
+    /// if it would needlessly cause itself to panic.
+    ///
+    /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
+    /// the requested space. This is not really unsafe, but the unsafe
+    /// code *you* write that relies on the behavior of this function may break.
+    ///
+    /// Returns true if the reallocation attempt has succeeded, or false otherwise.
+    ///
+    /// # Panics
+    ///
+    /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
+    /// * Panics on 32-bit platforms if the requested capacity exceeds
+    ///   `isize::MAX` bytes.
+    pub fn reserve_in_place(&mut self, used_cap: usize, needed_extra_cap: usize) -> bool {
+        unsafe {
+            // NOTE: we don't early branch on ZSTs here because we want this
+            // to actually catch "asking for more than usize::MAX" in that case.
+            // If we make it past the first branch then we are guaranteed to
+            // panic.
+
+            // Don't actually need any more capacity. If the current `cap` is 0, we can't
+            // reallocate in place.
+            // Wrapping in case they give a bad `used_cap`
+            let old_layout = match self.current_layout() {
+                Some(layout) => layout,
+                None => return false,
+            };
+            if self.cap().wrapping_sub(used_cap) >= needed_extra_cap {
+                return false;
+            }
+
+            let new_cap = self
+                .amortized_new_size(used_cap, needed_extra_cap)
+                .unwrap_or_else(|_| capacity_overflow());
+
+            // Here, `cap < used_cap + needed_extra_cap <= new_cap`
+            // (regardless of whether `self.cap - used_cap` wrapped).
+            // Therefore we can safely call grow_in_place.
+
+            let new_layout = Layout::new::<T>().repeat(new_cap).unwrap().0;
+            // FIXME: may crash and burn on over-reserve
+            alloc_guard(new_layout.size()).unwrap_or_else(|_| capacity_overflow());
+            match self
+                .a
+                .grow_in_place(self.ptr.cast(), old_layout, new_layout.size())
+            {
+                Ok(_) => {
+                    self.cap = new_cap;
+                    true
+                }
+                Err(_) => false,
+            }
+        }
+    }
+
+    /// Shrinks the allocation down to the specified amount. If the given amount
+    /// is 0, actually completely deallocates.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the given amount is *larger* than the current capacity.
+    ///
+    /// # Aborts
+    ///
+    /// Aborts on OOM.
+    pub fn shrink_to_fit(&mut self, amount: usize) {
+        let elem_size = mem::size_of::<T>();
+
+        // Set the `cap` because they might be about to promote to a `Box<[T]>`
+        if elem_size == 0 {
+            self.cap = amount;
+            return;
+        }
+
+        // This check is my waterloo; it's the only thing Vec wouldn't have to do.
+        assert!(self.cap >= amount, "Tried to shrink to a larger capacity");
+
+        if amount == 0 {
+            // We want to create a new zero-length vector within the
+            // same allocator.  We use ptr::write to avoid an
+            // erroneous attempt to drop the contents, and we use
+            // ptr::read to sidestep condition against destructuring
+            // types that implement Drop.
+
+            unsafe {
+                let a = self.a;
+                self.dealloc_buffer();
+                ptr::write(self, RawVec::new_in(a));
+            }
+        } else if self.cap != amount {
+            unsafe {
+                // We know here that our `amount` is greater than zero. This
+                // implies, via the assert above, that capacity is also greater
+                // than zero, which means that we've got a current layout that
+                // "fits"
+                //
+                // We also know that `self.cap` is greater than `amount`, and
+                // consequently we don't need runtime checks for creating either
+                // layout
+                let old_size = elem_size * self.cap;
+                let new_size = elem_size * amount;
+                let align = mem::align_of::<T>();
+                let old_layout = Layout::from_size_align_unchecked(old_size, align);
+                match self.a.realloc(self.ptr.cast(), old_layout, new_size) {
+                    Ok(p) => self.ptr = p.cast(),
+                    Err(_) => {
+                        handle_alloc_error(Layout::from_size_align_unchecked(new_size, align))
+                    }
+                }
+            }
+            self.cap = amount;
+        }
+    }
+}
+
+#[cfg(feature = "boxed")]
+impl<'a, T> RawVec<'a, T> {
+    /// Converts the entire buffer into `Box<[T]>`.
+    ///
+    /// Note that this will correctly reconstitute any `cap` changes
+    /// that may have been performed. (See description of type for details.)
+    ///
+    /// # Undefined Behavior
+    ///
+    /// All elements of `RawVec<T>` must be initialized. Notice that
+    /// the rules around uninitialized boxed values are not finalized yet,
+    /// but until they are, it is advisable to avoid them.
+    pub unsafe fn into_box(self) -> crate::boxed::Box<'a, [T]> {
+        use crate::boxed::Box;
+
+        // NOTE: not calling `cap()` here; actually using the real `cap` field!
+        let slice = core::slice::from_raw_parts_mut(self.ptr(), self.cap);
+        let output: Box<'a, [T]> = Box::from_raw(slice);
+        mem::forget(self);
+        output
+    }
+}
+
+enum Fallibility {
+    Fallible,
+    Infallible,
+}
+
+use self::Fallibility::*;
+
+enum ReserveStrategy {
+    Exact,
+    Amortized,
+}
+
+use self::ReserveStrategy::*;
+
+impl<'a, T> RawVec<'a, T> {
+    fn reserve_internal(
+        &mut self,
+        used_cap: usize,
+        needed_extra_cap: usize,
+        fallibility: Fallibility,
+        strategy: ReserveStrategy,
+    ) -> Result<(), CollectionAllocErr> {
+        unsafe {
+            use crate::AllocErr;
+
+            // NOTE: we don't early branch on ZSTs here because we want this
+            // to actually catch "asking for more than usize::MAX" in that case.
+            // If we make it past the first branch then we are guaranteed to
+            // panic.
+
+            // Don't actually need any more capacity.
+            // Wrapping in case they gave a bad `used_cap`.
+            if self.cap().wrapping_sub(used_cap) >= needed_extra_cap {
+                return Ok(());
+            }
+
+            // Nothing we can really do about these checks :(
+            let new_cap = match strategy {
+                Exact => used_cap
+                    .checked_add(needed_extra_cap)
+                    .ok_or(CapacityOverflow)?,
+                Amortized => self.amortized_new_size(used_cap, needed_extra_cap)?,
+            };
+            let new_layout = Layout::array::<T>(new_cap).map_err(|_| CapacityOverflow)?;
+
+            alloc_guard(new_layout.size())?;
+
+            let res = match self.current_layout() {
+                Some(layout) => {
+                    debug_assert!(new_layout.align() == layout.align());
+                    self.a.realloc(self.ptr.cast(), layout, new_layout.size())
+                }
+                None => Alloc::alloc(&mut self.a, new_layout),
+            };
+
+            if let (Err(AllocErr), Infallible) = (&res, fallibility) {
+                handle_alloc_error(new_layout);
+            }
+
+            self.ptr = res?.cast();
+            self.cap = new_cap;
+
+            Ok(())
+        }
+    }
+}
+
+impl<'a, T> RawVec<'a, T> {
+    /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
+    pub unsafe fn dealloc_buffer(&mut self) {
+        let elem_size = mem::size_of::<T>();
+        if elem_size != 0 {
+            if let Some(layout) = self.current_layout() {
+                self.a.dealloc(self.ptr.cast(), layout);
+            }
+        }
+    }
+}
+
+impl<'a, T> Drop for RawVec<'a, T> {
+    /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
+    fn drop(&mut self) {
+        unsafe {
+            self.dealloc_buffer();
+        }
+    }
+}
+
+// We need to guarantee the following:
+// * We don't ever allocate `> isize::MAX` byte-size objects
+// * We don't overflow `usize::MAX` and actually allocate too little
+//
+// On 64-bit we just need to check for overflow since trying to allocate
+// `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
+// an extra guard for this in case we're running on a platform which can use
+// all 4GB in user-space. e.g. PAE or x32
+
+#[inline]
+fn alloc_guard(alloc_size: usize) -> Result<(), CollectionAllocErr> {
+    if mem::size_of::<usize>() < 8 && alloc_size > ::core::isize::MAX as usize {
+        Err(CapacityOverflow)
+    } else {
+        Ok(())
+    }
+}
+
+// One central function responsible for reporting capacity overflows. This'll
+// ensure that the code generation related to these panics is minimal as there's
+// only one location which panics rather than a bunch throughout the module.
+fn capacity_overflow() -> ! {
+    panic!("capacity overflow")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn reserve_does_not_overallocate() {
+        let bump = Bump::new();
+        {
+            let mut v: RawVec<u32> = RawVec::new_in(&bump);
+            // First `reserve` allocates like `reserve_exact`
+            v.reserve(0, 9);
+            assert_eq!(9, v.cap());
+        }
+
+        {
+            let mut v: RawVec<u32> = RawVec::new_in(&bump);
+            v.reserve(0, 7);
+            assert_eq!(7, v.cap());
+            // 97 if more than double of 7, so `reserve` should work
+            // like `reserve_exact`.
+            v.reserve(7, 90);
+            assert_eq!(97, v.cap());
+        }
+
+        {
+            let mut v: RawVec<u32> = RawVec::new_in(&bump);
+            v.reserve(0, 12);
+            assert_eq!(12, v.cap());
+            v.reserve(12, 3);
+            // 3 is less than half of 12, so `reserve` must grow
+            // exponentially. At the time of writing this test grow
+            // factor is 2, so new capacity is 24, however, grow factor
+            // of 1.5 is OK too. Hence `>= 18` in assert.
+            assert!(v.cap() >= 12 + 12 / 2);
+        }
+    }
+}
diff --git a/third_party/rust/bumpalo/src/collections/str/lossy.rs b/third_party/rust/bumpalo/src/collections/str/lossy.rs
new file mode 100644
index 0000000000..b1012a4129
--- /dev/null
+++ b/third_party/rust/bumpalo/src/collections/str/lossy.rs
@@ -0,0 +1,209 @@
+// Copyright 2012-2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use crate::collections::str as core_str;
+use core::char;
+use core::fmt;
+use core::fmt::Write;
+use core::str;
+
+/// Lossy UTF-8 string.
+pub struct Utf8Lossy<'a> {
+    bytes: &'a [u8],
+}
+
+impl<'a> Utf8Lossy<'a> {
+    pub fn from_bytes(bytes: &'a [u8]) -> Utf8Lossy<'a> {
+        Utf8Lossy { bytes }
+    }
+
+    pub fn chunks(&self) -> Utf8LossyChunksIter<'a> {
+        Utf8LossyChunksIter {
+            source: &self.bytes,
+        }
+    }
+}
+
+/// Iterator over lossy UTF-8 string
+#[allow(missing_debug_implementations)]
+pub struct Utf8LossyChunksIter<'a> {
+    source: &'a [u8],
+}
+
+#[derive(PartialEq, Eq, Debug)]
+pub struct Utf8LossyChunk<'a> {
+    /// Sequence of valid chars.
+    /// Can be empty between broken UTF-8 chars.
+    pub valid: &'a str,
+    /// Single broken char, empty if none.
+    /// Empty iff iterator item is last.
+    pub broken: &'a [u8],
+}
+
+impl<'a> Iterator for Utf8LossyChunksIter<'a> {
+    type Item = Utf8LossyChunk<'a>;
+
+    fn next(&mut self) -> Option<Utf8LossyChunk<'a>> {
+        if self.source.is_empty() {
+            return None;
+        }
+
+        const TAG_CONT_U8: u8 = 128;
+        fn unsafe_get(xs: &[u8], i: usize) -> u8 {
+            unsafe { *xs.get_unchecked(i) }
+        }
+        fn safe_get(xs: &[u8], i: usize) -> u8 {
+            if i >= xs.len() {
+                0
+            } else {
+                unsafe_get(xs, i)
+            }
+        }
+
+        let mut i = 0;
+        while i < self.source.len() {
+            let i_ = i;
+
+            let byte = unsafe_get(self.source, i);
+            i += 1;
+
+            if byte < 128 {
+            } else {
+                let w = core_str::utf8_char_width(byte);
+
+                macro_rules! error {
+                    () => {{
+                        unsafe {
+                            let r = Utf8LossyChunk {
+                                valid: str::from_utf8_unchecked(&self.source[0..i_]),
+                                broken: &self.source[i_..i],
+                            };
+                            self.source = &self.source[i..];
+                            return Some(r);
+                        }
+                    }};
+                }
+
+                match w {
+                    2 => {
+                        if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
+                            error!();
+                        }
+                        i += 1;
+                    }
+                    3 => {
+                        match (byte, safe_get(self.source, i)) {
+                            (0xE0, 0xA0..=0xBF) => (),
+                            (0xE1..=0xEC, 0x80..=0xBF) => (),
+                            (0xED, 0x80..=0x9F) => (),
+                            (0xEE..=0xEF, 0x80..=0xBF) => (),
+                            _ => {
+                                error!();
+                            }
+                        }
+                        i += 1;
+                        if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
+                            error!();
+                        }
+                        i += 1;
+                    }
+                    4 => {
+                        match (byte, safe_get(self.source, i)) {
+                            (0xF0, 0x90..=0xBF) => (),
+                            (0xF1..=0xF3, 0x80..=0xBF) => (),
+                            (0xF4, 0x80..=0x8F) => (),
+                            _ => {
+                                error!();
+                            }
+                        }
+                        i += 1;
+                        if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
+                            error!();
+                        }
+                        i += 1;
+                        if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
+                            error!();
+                        }
+                        i += 1;
+                    }
+                    _ => {
+                        error!();
+                    }
+                }
+            }
+        }
+
+        let r = Utf8LossyChunk {
+            valid: unsafe { str::from_utf8_unchecked(self.source) },
+            broken: &[],
+        };
+        self.source = &[];
+        Some(r)
+    }
+}
+
+impl<'a> fmt::Display for Utf8Lossy<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // If we're the empty string then our iterator won't actually yield
+        // anything, so perform the formatting manually
+        if self.bytes.is_empty() {
+            return "".fmt(f);
+        }
+
+        for Utf8LossyChunk { valid, broken } in self.chunks() {
+            // If we successfully decoded the whole chunk as a valid string then
+            // we can return a direct formatting of the string which will also
+            // respect various formatting flags if possible.
+            if valid.len() == self.bytes.len() {
+                assert!(broken.is_empty());
+                return valid.fmt(f);
+            }
+
+            f.write_str(valid)?;
+            if !broken.is_empty() {
+                f.write_char(char::REPLACEMENT_CHARACTER)?;
+            }
+        }
+        Ok(())
+    }
+}
+
+impl<'a> fmt::Debug for Utf8Lossy<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_char('"')?;
+
+        for Utf8LossyChunk { valid, broken } in self.chunks() {
+            // Valid part.
+            // Here we partially parse UTF-8 again which is suboptimal.
+            {
+                let mut from = 0;
+                for (i, c) in valid.char_indices() {
+                    let esc = c.escape_debug();
+                    // If char needs escaping, flush backlog so far and write, else skip
+                    if esc.len() != 1 {
+                        f.write_str(&valid[from..i])?;
+                        for c in esc {
+                            f.write_char(c)?;
+                        }
+                        from = i + c.len_utf8();
+                    }
+                }
+                f.write_str(&valid[from..])?;
+            }
+
+            // Broken parts of string as hex escape.
+            for &b in broken {
+                write!(f, "\\x{:02x}", b)?;
+            }
+        }
+
+        f.write_char('"')
+    }
+}
diff --git a/third_party/rust/bumpalo/src/collections/str/mod.rs b/third_party/rust/bumpalo/src/collections/str/mod.rs
new file mode 100644
index 0000000000..29f4c6be06
--- /dev/null
+++ b/third_party/rust/bumpalo/src/collections/str/mod.rs
@@ -0,0 +1,43 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! String manipulation
+//!
+//! For more details, see std::str
+
+#[allow(missing_docs)]
+pub mod lossy;
+
+// https://tools.ietf.org/html/rfc3629
+#[rustfmt::skip]
+static UTF8_CHAR_WIDTH: [u8; 256] = [
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x1F
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x3F
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x5F
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x7F
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0x9F
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0xBF
+0,0,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
+2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // 0xDF
+3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3, // 0xEF
+4,4,4,4,4,0,0,0,0,0,0,0,0,0,0,0, // 0xFF
+];
+
+/// Given a first byte, determines how many bytes are in this UTF-8 character.
+#[inline]
+pub fn utf8_char_width(b: u8) -> usize {
+    UTF8_CHAR_WIDTH[b as usize] as usize
+}
diff --git a/third_party/rust/bumpalo/src/collections/string.rs b/third_party/rust/bumpalo/src/collections/string.rs
new file mode 100644
index 0000000000..6b7af9a4b7
--- /dev/null
+++ b/third_party/rust/bumpalo/src/collections/string.rs
@@ -0,0 +1,2123 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A UTF-8 encoded, growable string.
+//!
+//! This module contains the [`String`] type and several error types that may
+//! result from working with [`String`]s.
+//!
+//! This module is a fork of the [`std::string`] module, that uses a bump allocator.
+//!
+//! [`std::string`]: https://doc.rust-lang.org/std/string/index.html
+//!
+//! # Examples
+//!
+//! You can create a new [`String`] from a string literal with [`String::from_str_in`]:
+//!
+//! ```
+//! use bumpalo::{Bump, collections::String};
+//!
+//! let b = Bump::new();
+//!
+//! let s = String::from_str_in("world", &b);
+//! ```
+//!
+//! [`String`]: struct.String.html
+//! [`String::from_str_in`]: struct.String.html#method.from_str_in
+//!
+//! If you have a vector of valid UTF-8 bytes, you can make a [`String`] out of
+//! it. You can do the reverse too.
+//!
+//! ```
+//! use bumpalo::{Bump, collections::String};
+//!
+//! let b = Bump::new();
+//!
+//! let sparkle_heart = bumpalo::vec![in &b; 240, 159, 146, 150];
+//!
+//! // We know these bytes are valid, so we'll use `unwrap()`.
+//! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
+//!
+//! assert_eq!("💖", sparkle_heart);
+//!
+//! let bytes = sparkle_heart.into_bytes();
+//!
+//! assert_eq!(bytes, [240, 159, 146, 150]);
+//! ```
+
+use crate::collections::str::lossy;
+use crate::collections::vec::Vec;
+use crate::Bump;
+use core::borrow::{Borrow, BorrowMut};
+use core::char::decode_utf16;
+use core::fmt;
+use core::hash;
+use core::iter::FusedIterator;
+use core::mem;
+use core::ops::Bound::{Excluded, Included, Unbounded};
+use core::ops::{self, Add, AddAssign, Index, IndexMut, RangeBounds};
+use core::ptr;
+use core::str::{self, Chars, Utf8Error};
+use core_alloc::borrow::Cow;
+
+/// Like the [`format!`] macro, but for creating [`bumpalo::collections::String`]s.
+///
+/// [`format!`]: https://doc.rust-lang.org/std/macro.format.html
+/// [`bumpalo::collections::String`]: collections/string/struct.String.html
+///
+/// # Examples
+///
+/// ```
+/// use bumpalo::Bump;
+///
+/// let b = Bump::new();
+///
+/// let who = "World";
+/// let s = bumpalo::format!(in &b, "Hello, {}!", who);
+/// assert_eq!(s, "Hello, World!")
+/// ```
+#[macro_export]
+macro_rules! format {
+    ( in $bump:expr, $fmt:expr, $($args:expr),* ) => {{
+        use $crate::core_alloc::fmt::Write;
+        let bump = $bump;
+        let mut s = $crate::collections::String::new_in(bump);
+        let _ = write!(&mut s, $fmt, $($args),*);
+        s
+    }};
+
+    ( in $bump:expr, $fmt:expr, $($args:expr,)* ) => {
+        $crate::format!(in $bump, $fmt, $($args),*)
+    };
+}
+
+/// A UTF-8 encoded, growable string.
+///
+/// The `String` type is the most common string type that has ownership over the
+/// contents of the string. It has a close relationship with its borrowed
+/// counterpart, the primitive [`str`].
+///
+/// [`str`]: https://doc.rust-lang.org/std/primitive.str.html
+///
+/// # Examples
+///
+/// You can create a `String` from a literal string with [`String::from_str_in`]:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// let hello = String::from_str_in("Hello, world!", &b);
+/// ```
+///
+/// You can append a [`char`] to a `String` with the [`push`] method, and
+/// append a [`&str`] with the [`push_str`] method:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// let mut hello = String::from_str_in("Hello, ", &b);
+///
+/// hello.push('w');
+/// hello.push_str("orld!");
+/// ```
+///
+/// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+/// [`push`]: #method.push
+/// [`push_str`]: #method.push_str
+///
+/// If you have a vector of UTF-8 bytes, you can create a `String` from it with
+/// the [`from_utf8`] method:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// // some bytes, in a vector
+/// let sparkle_heart = bumpalo::vec![in &b; 240, 159, 146, 150];
+///
+/// // We know these bytes are valid, so we'll use `unwrap()`.
+/// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
+///
+/// assert_eq!("💖", sparkle_heart);
+/// ```
+///
+/// [`from_utf8`]: #method.from_utf8
+///
+/// # Deref
+///
+/// `String`s implement <code>[`Deref`]<Target = [`str`]></code>, and so inherit all of [`str`]'s
+/// methods. In addition, this means that you can pass a `String` to a
+/// function which takes a [`&str`] by using an ampersand (`&`):
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// fn takes_str(s: &str) { }
+///
+/// let s = String::from_str_in("Hello", &b);
+///
+/// takes_str(&s);
+/// ```
+///
+/// This will create a [`&str`] from the `String` and pass it in. This
+/// conversion is very inexpensive, and so generally, functions will accept
+/// [`&str`]s as arguments unless they need a `String` for some specific
+/// reason.
+///
+/// In certain cases Rust doesn't have enough information to make this
+/// conversion, known as [`Deref`] coercion. In the following example a string
+/// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
+/// `example_func` takes anything that implements the trait. In this case Rust
+/// would need to make two implicit conversions, which Rust doesn't have the
+/// means to do. For that reason, the following example will not compile.
+///
+/// ```compile_fail,E0277
+/// use bumpalo::{Bump, collections::String};
+///
+/// trait TraitExample {}
+///
+/// impl<'a> TraitExample for &'a str {}
+///
+/// fn example_func<A: TraitExample>(example_arg: A) {}
+///
+/// let b = Bump::new();
+/// let example_string = String::from_str_in("example_string", &b);
+/// example_func(&example_string);
+/// ```
+///
+/// There are two options that would work instead. The first would be to
+/// change the line `example_func(&example_string);` to
+/// `example_func(example_string.as_str());`, using the method [`as_str()`]
+/// to explicitly extract the string slice containing the string. The second
+/// way changes `example_func(&example_string);` to
+/// `example_func(&*example_string);`. In this case we are dereferencing a
+/// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
+/// [`&str`]. The second way is more idiomatic, however both work to do the
+/// conversion explicitly rather than relying on the implicit conversion.
+///
+/// # Representation
+///
+/// A `String` is made up of three components: a pointer to some bytes, a
+/// length, and a capacity. The pointer points to an internal buffer `String`
+/// uses to store its data. The length is the number of bytes currently stored
+/// in the buffer, and the capacity is the size of the buffer in bytes. As such,
+/// the length will always be less than or equal to the capacity.
+///
+/// This buffer is always stored on the heap.
+///
+/// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
+/// methods:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+/// use std::mem;
+///
+/// let b = Bump::new();
+///
+/// let mut story = String::from_str_in("Once upon a time...", &b);
+///
+/// let ptr = story.as_mut_ptr();
+/// let len = story.len();
+/// let capacity = story.capacity();
+///
+/// // story has nineteen bytes
+/// assert_eq!(19, len);
+///
+/// // Now that we have our parts, we throw the story away.
+/// mem::forget(story);
+///
+/// // We can re-build a String out of ptr, len, and capacity. This is all
+/// // unsafe because we are responsible for making sure the components are
+/// // valid:
+/// let s = unsafe { String::from_raw_parts_in(ptr, len, capacity, &b) } ;
+///
+/// assert_eq!(String::from_str_in("Once upon a time...", &b), s);
+/// ```
+///
+/// [`as_ptr`]: https://doc.rust-lang.org/std/primitive.str.html#method.as_ptr
+/// [`len`]: #method.len
+/// [`capacity`]: #method.capacity
+///
+/// If a `String` has enough capacity, adding elements to it will not
+/// re-allocate. For example, consider this program:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// let mut s = String::new_in(&b);
+///
+/// println!("{}", s.capacity());
+///
+/// for _ in 0..5 {
+///     s.push_str("hello");
+///     println!("{}", s.capacity());
+/// }
+/// ```
+///
+/// This will output the following:
+///
+/// ```text
+/// 0
+/// 5
+/// 10
+/// 20
+/// 20
+/// 40
+/// ```
+///
+/// At first, we have no memory allocated at all, but as we append to the
+/// string, it increases its capacity appropriately. If we instead use the
+/// [`with_capacity_in`] method to allocate the correct capacity initially:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// let mut s = String::with_capacity_in(25, &b);
+///
+/// println!("{}", s.capacity());
+///
+/// for _ in 0..5 {
+///     s.push_str("hello");
+///     println!("{}", s.capacity());
+/// }
+/// ```
+///
+/// [`with_capacity_in`]: #method.with_capacity_in
+///
+/// We end up with a different output:
+///
+/// ```text
+/// 25
+/// 25
+/// 25
+/// 25
+/// 25
+/// 25
+/// ```
+///
+/// Here, there's no need to allocate more memory inside the loop.
+///
+/// [`&str`]: https://doc.rust-lang.org/std/primitive.str.html
+/// [`Deref`]: https://doc.rust-lang.org/std/ops/trait.Deref.html
+/// [`as_str()`]: struct.String.html#method.as_str
+#[derive(PartialOrd, Eq, Ord)]
+pub struct String<'bump> {
+    vec: Vec<'bump, u8>,
+}
+
+/// A possible error value when converting a `String` from a UTF-8 byte vector.
+///
+/// This type is the error type for the [`from_utf8`] method on [`String`]. It
+/// is designed in such a way to carefully avoid reallocations: the
+/// [`into_bytes`] method will give back the byte vector that was used in the
+/// conversion attempt.
+///
+/// [`from_utf8`]: struct.String.html#method.from_utf8
+/// [`String`]: struct.String.html
+/// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
+///
+/// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
+/// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
+/// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
+/// through the [`utf8_error`] method.
+///
+/// [`Utf8Error`]: https://doc.rust-lang.org/std/str/struct.Utf8Error.html
+/// [`std::str`]: https://doc.rust-lang.org/std/str/index.html
+/// [`u8`]: https://doc.rust-lang.org/std/primitive.u8.html
+/// [`&str`]: https://doc.rust-lang.org/std/primitive.str.html
+/// [`utf8_error`]: #method.utf8_error
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// // some invalid bytes, in a vector
+/// let bytes = bumpalo::vec![in &b; 0, 159];
+///
+/// let value = String::from_utf8(bytes);
+///
+/// assert!(value.is_err());
+/// assert_eq!(bumpalo::vec![in &b; 0, 159], value.unwrap_err().into_bytes());
+/// ```
+#[derive(Debug)]
+pub struct FromUtf8Error<'bump> {
+    bytes: Vec<'bump, u8>,
+    error: Utf8Error,
+}
+
+/// A possible error value when converting a `String` from a UTF-16 byte slice.
+///
+/// This type is the error type for the [`from_utf16_in`] method on [`String`].
+///
+/// [`from_utf16_in`]: struct.String.html#method.from_utf16_in
+/// [`String`]: struct.String.html
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let b = Bump::new();
+///
+/// // 𝄞mu<invalid>ic
+/// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0xD800, 0x0069, 0x0063];
+///
+/// assert!(String::from_utf16_in(v, &b).is_err());
+/// ```
+#[derive(Debug)]
+pub struct FromUtf16Error(());
+
+impl<'bump> String<'bump> {
+    /// Creates a new empty `String`.
+    ///
+    /// Given that the `String` is empty, this will not allocate any initial
+    /// buffer. While that means that this initial operation is very
+    /// inexpensive, it may cause excessive allocation later when you add
+    /// data. If you have an idea of how much data the `String` will hold,
+    /// consider the [`with_capacity_in`] method to prevent excessive
+    /// re-allocation.
+    ///
+    /// [`with_capacity_in`]: #method.with_capacity_in
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::new_in(&b);
+    /// ```
+    #[inline]
+    pub fn new_in(bump: &'bump Bump) -> String<'bump> {
+        String {
+            vec: Vec::new_in(bump),
+        }
+    }
+
+    /// Creates a new empty `String` with a particular capacity.
+    ///
+    /// `String`s have an internal buffer to hold their data. The capacity is
+    /// the length of that buffer, and can be queried with the [`capacity`]
+    /// method. This method creates an empty `String`, but one with an initial
+    /// buffer that can hold `capacity` bytes. This is useful when you may be
+    /// appending a bunch of data to the `String`, reducing the number of
+    /// reallocations it needs to do.
+    ///
+    /// [`capacity`]: #method.capacity
+    ///
+    /// If the given capacity is `0`, no allocation will occur, and this method
+    /// is identical to the [`new_in`] method.
+    ///
+    /// [`new_in`]: #method.new
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::with_capacity_in(10, &b);
+    ///
+    /// // The String contains no chars, even though it has capacity for more
+    /// assert_eq!(s.len(), 0);
+    ///
+    /// // These are all done without reallocating...
+    /// let cap = s.capacity();
+    /// for _ in 0..10 {
+    ///     s.push('a');
+    /// }
+    ///
+    /// assert_eq!(s.capacity(), cap);
+    ///
+    /// // ...but this may make the vector reallocate
+    /// s.push('a');
+    /// ```
+    #[inline]
+    pub fn with_capacity_in(capacity: usize, bump: &'bump Bump) -> String<'bump> {
+        String {
+            vec: Vec::with_capacity_in(capacity, bump),
+        }
+    }
+
+    /// Converts a vector of bytes to a `String`.
+    ///
+    /// A string (`String`) is made of bytes ([`u8`]), and a vector of bytes
+    /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
+    /// two. Not all byte slices are valid `String`s, however: `String`
+    /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
+    /// the bytes are valid UTF-8, and then does the conversion.
+    ///
+    /// If you are sure that the byte slice is valid UTF-8, and you don't want
+    /// to incur the overhead of the validity check, there is an unsafe version
+    /// of this function, [`from_utf8_unchecked`], which has the same behavior
+    /// but skips the check.
+    ///
+    /// This method will take care to not copy the vector, for efficiency's
+    /// sake.
+    ///
+    /// If you need a [`&str`] instead of a `String`, consider
+    /// [`str::from_utf8`].
+    ///
+    /// The inverse of this method is [`into_bytes`].
+    ///
+    /// # Errors
+    ///
+    /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
+    /// provided bytes are not UTF-8. The vector you moved in is also included.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some bytes, in a vector
+    /// let sparkle_heart = bumpalo::vec![in &b; 240, 159, 146, 150];
+    ///
+    /// // We know these bytes are valid, so we'll use `unwrap()`.
+    /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
+    ///
+    /// assert_eq!("💖", sparkle_heart);
+    /// ```
+    ///
+    /// Incorrect bytes:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some invalid bytes, in a vector
+    /// let sparkle_heart = bumpalo::vec![in &b; 0, 159, 146, 150];
+    ///
+    /// assert!(String::from_utf8(sparkle_heart).is_err());
+    /// ```
+    ///
+    /// See the docs for [`FromUtf8Error`] for more details on what you can do
+    /// with this error.
+    ///
+    /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
+    /// [`&str`]: https://doc.rust-lang.org/std/primitive.str.html
+    /// [`u8`]: https://doc.rust-lang.org/std/primitive.u8.html
+    /// [`Vec<u8>`]: ../vec/struct.Vec.html
+    /// [`str::from_utf8`]: https://doc.rust-lang.org/std/str/fn.from_utf8.html
+    /// [`into_bytes`]: struct.String.html#method.into_bytes
+    /// [`FromUtf8Error`]: struct.FromUtf8Error.html
+    /// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
+    #[inline]
+    pub fn from_utf8(vec: Vec<'bump, u8>) -> Result<String<'bump>, FromUtf8Error<'bump>> {
+        match str::from_utf8(&vec) {
+            Ok(..) => Ok(String { vec }),
+            Err(e) => Err(FromUtf8Error {
+                bytes: vec,
+                error: e,
+            }),
+        }
+    }
+
+    /// Converts a slice of bytes to a string, including invalid characters.
+    ///
+    /// Strings are made of bytes ([`u8`]), and a slice of bytes
+    /// ([`&[u8]`][slice]) is made of bytes, so this function converts
+    /// between the two. Not all byte slices are valid strings, however: strings
+    /// are required to be valid UTF-8. During this conversion,
+    /// `from_utf8_lossy_in()` will replace any invalid UTF-8 sequences with
+    /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: �
+    ///
+    /// [`u8`]: https://doc.rust-lang.org/std/primitive.u8.html
+    /// [slice]: https://doc.rust-lang.org/std/primitive.slice.html
+    /// [U+FFFD]: https://doc.rust-lang.org/std/char/constant.REPLACEMENT_CHARACTER.html
+    ///
+    /// If you are sure that the byte slice is valid UTF-8, and you don't want
+    /// to incur the overhead of the conversion, there is an unsafe version
+    /// of this function, [`from_utf8_unchecked`], which has the same behavior
+    /// but skips the checks.
+    ///
+    /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{collections::String, Bump, vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some bytes, in a vector
+    /// let sparkle_heart = bumpalo::vec![in &b; 240, 159, 146, 150];
+    ///
+    /// let sparkle_heart = String::from_utf8_lossy_in(&sparkle_heart, &b);
+    ///
+    /// assert_eq!("💖", sparkle_heart);
+    /// ```
+    ///
+    /// Incorrect bytes:
+    ///
+    /// ```
+    /// use bumpalo::{collections::String, Bump, vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some invalid bytes
+    /// let input = b"Hello \xF0\x90\x80World";
+    /// let output = String::from_utf8_lossy_in(input, &b);
+    ///
+    /// assert_eq!("Hello �World", output);
+    /// ```
+    pub fn from_utf8_lossy_in(v: &[u8], bump: &'bump Bump) -> String<'bump> {
+        let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
+
+        let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
+            let lossy::Utf8LossyChunk { valid, broken } = chunk;
+            if valid.len() == v.len() {
+                debug_assert!(broken.is_empty());
+                unsafe {
+                    return String::from_utf8_unchecked(Vec::from_iter_in(v.iter().cloned(), bump));
+                }
+            }
+            (valid, broken)
+        } else {
+            return String::from_str_in("", bump);
+        };
+
+        const REPLACEMENT: &str = "\u{FFFD}";
+
+        let mut res = String::with_capacity_in(v.len(), bump);
+        res.push_str(first_valid);
+        if !first_broken.is_empty() {
+            res.push_str(REPLACEMENT);
+        }
+
+        for lossy::Utf8LossyChunk { valid, broken } in iter {
+            res.push_str(valid);
+            if !broken.is_empty() {
+                res.push_str(REPLACEMENT);
+            }
+        }
+
+        res
+    }
+
+    /// Decode a UTF-16 encoded slice `v` into a `String`, returning [`Err`]
+    /// if `v` contains any invalid data.
+    ///
+    /// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // 𝄞music
+    /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0x0069, 0x0063];
+    /// assert_eq!(String::from_str_in("𝄞music", &b), String::from_utf16_in(v, &b).unwrap());
+    ///
+    /// // 𝄞mu<invalid>ic
+    /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0xD800, 0x0069, 0x0063];
+    /// assert!(String::from_utf16_in(v, &b).is_err());
+    /// ```
+    pub fn from_utf16_in(v: &[u16], bump: &'bump Bump) -> Result<String<'bump>, FromUtf16Error> {
+        let mut ret = String::with_capacity_in(v.len(), bump);
+        for c in decode_utf16(v.iter().cloned()) {
+            if let Ok(c) = c {
+                ret.push(c);
+            } else {
+                return Err(FromUtf16Error(()));
+            }
+        }
+        Ok(ret)
+    }
+
+    /// Construct a new `String<'bump>` from a string slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::from_str_in("hello", &b);
+    /// assert_eq!(s, "hello");
+    /// ```
+    pub fn from_str_in(s: &str, bump: &'bump Bump) -> String<'bump> {
+        let mut t = String::with_capacity_in(s.len(), bump);
+        t.push_str(s);
+        t
+    }
+
+    /// Construct a new `String<'bump>` from an iterator of `char`s.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::from_iter_in(['h', 'e', 'l', 'l', 'o'].iter().cloned(), &b);
+    /// assert_eq!(s, "hello");
+    /// ```
+    pub fn from_iter_in<I: IntoIterator<Item = char>>(iter: I, bump: &'bump Bump) -> String<'bump> {
+        let mut s = String::new_in(bump);
+        for c in iter {
+            s.push(c);
+        }
+        s
+    }
+
+    /// Creates a new `String` from a length, capacity, and pointer.
+    ///
+    /// # Safety
+    ///
+    /// This is highly unsafe, due to the number of invariants that aren't
+    /// checked:
+    ///
+    /// * The memory at `ptr` needs to have been previously allocated by the
+    ///   same allocator the standard library uses.
+    /// * `length` needs to be less than or equal to `capacity`.
+    /// * `capacity` needs to be the correct value.
+    ///
+    /// Violating these may cause problems like corrupting the allocator's
+    /// internal data structures.
+    ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `String` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    /// use std::mem;
+    ///
+    /// let b = Bump::new();
+    ///
+    /// unsafe {
+    ///     let mut s = String::from_str_in("hello", &b);
+    ///     let ptr = s.as_mut_ptr();
+    ///     let len = s.len();
+    ///     let capacity = s.capacity();
+    ///
+    ///     mem::forget(s);
+    ///
+    ///     let s = String::from_raw_parts_in(ptr, len, capacity, &b);
+    ///
+    ///     assert_eq!(s, "hello");
+    /// }
+    /// ```
+    #[inline]
+    pub unsafe fn from_raw_parts_in(
+        buf: *mut u8,
+        length: usize,
+        capacity: usize,
+        bump: &'bump Bump,
+    ) -> String<'bump> {
+        String {
+            vec: Vec::from_raw_parts_in(buf, length, capacity, bump),
+        }
+    }
+
+    /// Converts a vector of bytes to a `String` without checking that the
+    /// string contains valid UTF-8.
+    ///
+    /// See the safe version, [`from_utf8`], for more details.
+    ///
+    /// [`from_utf8`]: struct.String.html#method.from_utf8
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because it does not check that the bytes passed
+    /// to it are valid UTF-8. If this constraint is violated, it may cause
+    /// memory unsafety issues with future users of the `String`,
+    /// as it is assumed that `String`s are valid UTF-8.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some bytes, in a vector
+    /// let sparkle_heart = bumpalo::vec![in &b; 240, 159, 146, 150];
+    ///
+    /// let sparkle_heart = unsafe {
+    ///     String::from_utf8_unchecked(sparkle_heart)
+    /// };
+    ///
+    /// assert_eq!("💖", sparkle_heart);
+    /// ```
+    #[inline]
+    pub unsafe fn from_utf8_unchecked(bytes: Vec<'bump, u8>) -> String<'bump> {
+        String { vec: bytes }
+    }
+
+    /// Converts a `String` into a byte vector.
+    ///
+    /// This consumes the `String`, so we do not need to copy its contents.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::from_str_in("hello", &b);
+    ///
+    /// assert_eq!(s.into_bytes(), [104, 101, 108, 108, 111]);
+    /// ```
+    #[inline]
+    pub fn into_bytes(self) -> Vec<'bump, u8> {
+        self.vec
+    }
+
+    /// Convert this `String<'bump>` into a `&'bump str`. This is analogous to
+    /// [`std::string::String::into_boxed_str`][into_boxed_str].
+    ///
+    /// [into_boxed_str]: https://doc.rust-lang.org/std/string/struct.String.html#method.into_boxed_str
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::from_str_in("foo", &b);
+    ///
+    /// assert_eq!(s.into_bump_str(), "foo");
+    /// ```
+    pub fn into_bump_str(self) -> &'bump str {
+        let s = unsafe {
+            let s = self.as_str();
+            mem::transmute(s)
+        };
+        mem::forget(self);
+        s
+    }
+
+    /// Extracts a string slice containing the entire `String`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::from_str_in("foo", &b);
+    ///
+    /// assert_eq!("foo", s.as_str());
+    /// ```
+    #[inline]
+    pub fn as_str(&self) -> &str {
+        self
+    }
+
+    /// Converts a `String` into a mutable string slice.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("foobar", &b);
+    /// let s_mut_str = s.as_mut_str();
+    ///
+    /// s_mut_str.make_ascii_uppercase();
+    ///
+    /// assert_eq!("FOOBAR", s_mut_str);
+    /// ```
+    #[inline]
+    pub fn as_mut_str(&mut self) -> &mut str {
+        self
+    }
+
+    /// Appends a given string slice onto the end of this `String`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("foo", &b);
+    ///
+    /// s.push_str("bar");
+    ///
+    /// assert_eq!("foobar", s);
+    /// ```
+    #[inline]
+    pub fn push_str(&mut self, string: &str) {
+        self.vec.extend_from_slice(string.as_bytes())
+    }
+
+    /// Returns this `String`'s capacity, in bytes.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::with_capacity_in(10, &b);
+    ///
+    /// assert!(s.capacity() >= 10);
+    /// ```
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        self.vec.capacity()
+    }
+
+    /// Ensures that this `String`'s capacity is at least `additional` bytes
+    /// larger than its length.
+    ///
+    /// The capacity may be increased by more than `additional` bytes if it
+    /// chooses, to prevent frequent reallocations.
+    ///
+    /// If you do not want this "at least" behavior, see the [`reserve_exact`]
+    /// method.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows [`usize`].
+    ///
+    /// [`reserve_exact`]: struct.String.html#method.reserve_exact
+    /// [`usize`]: https://doc.rust-lang.org/std/primitive.usize.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::new_in(&b);
+    ///
+    /// s.reserve(10);
+    ///
+    /// assert!(s.capacity() >= 10);
+    /// ```
+    ///
+    /// This may not actually increase the capacity:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::with_capacity_in(10, &b);
+    /// s.push('a');
+    /// s.push('b');
+    ///
+    /// // s now has a length of 2 and a capacity of 10
+    /// assert_eq!(2, s.len());
+    /// assert_eq!(10, s.capacity());
+    ///
+    /// // Since we already have an extra 8 capacity, calling this...
+    /// s.reserve(8);
+    ///
+    /// // ... doesn't actually increase.
+    /// assert_eq!(10, s.capacity());
+    /// ```
+    #[inline]
+    pub fn reserve(&mut self, additional: usize) {
+        self.vec.reserve(additional)
+    }
+
+    /// Ensures that this `String`'s capacity is `additional` bytes
+    /// larger than its length.
+    ///
+    /// Consider using the [`reserve`] method unless you absolutely know
+    /// better than the allocator.
+    ///
+    /// [`reserve`]: #method.reserve
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::new_in(&b);
+    ///
+    /// s.reserve_exact(10);
+    ///
+    /// assert!(s.capacity() >= 10);
+    /// ```
+    ///
+    /// This may not actually increase the capacity:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::with_capacity_in(10, &b);
+    /// s.push('a');
+    /// s.push('b');
+    ///
+    /// // s now has a length of 2 and a capacity of 10
+    /// assert_eq!(2, s.len());
+    /// assert_eq!(10, s.capacity());
+    ///
+    /// // Since we already have an extra 8 capacity, calling this...
+    /// s.reserve_exact(8);
+    ///
+    /// // ... doesn't actually increase.
+    /// assert_eq!(10, s.capacity());
+    /// ```
+    #[inline]
+    pub fn reserve_exact(&mut self, additional: usize) {
+        self.vec.reserve_exact(additional)
+    }
+
+    /// Shrinks the capacity of this `String` to match its length.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("foo", &b);
+    ///
+    /// s.reserve(100);
+    /// assert!(s.capacity() >= 100);
+    ///
+    /// s.shrink_to_fit();
+    /// assert_eq!(3, s.capacity());
+    /// ```
+    #[inline]
+    pub fn shrink_to_fit(&mut self) {
+        self.vec.shrink_to_fit()
+    }
+
+    /// Appends the given [`char`] to the end of this `String`.
+    ///
+    /// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("abc", &b);
+    ///
+    /// s.push('1');
+    /// s.push('2');
+    /// s.push('3');
+    ///
+    /// assert_eq!("abc123", s);
+    /// ```
+    #[inline]
+    pub fn push(&mut self, ch: char) {
+        match ch.len_utf8() {
+            1 => self.vec.push(ch as u8),
+            _ => self
+                .vec
+                .extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
+        }
+    }
+
+    /// Returns a byte slice of this `String`'s contents.
+    ///
+    /// The inverse of this method is [`from_utf8`].
+    ///
+    /// [`from_utf8`]: #method.from_utf8
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let s = String::from_str_in("hello", &b);
+    ///
+    /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
+    /// ```
+    #[inline]
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.vec
+    }
+
+    /// Shortens this `String` to the specified length.
+    ///
+    /// If `new_len` is greater than the string's current length, this has no
+    /// effect.
+    ///
+    /// Note that this method has no effect on the allocated capacity
+    /// of the string.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `new_len` does not lie on a [`char`] boundary.
+    ///
+    /// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("hello", &b);
+    ///
+    /// s.truncate(2);
+    ///
+    /// assert_eq!("he", s);
+    /// ```
+    #[inline]
+    pub fn truncate(&mut self, new_len: usize) {
+        if new_len <= self.len() {
+            assert!(self.is_char_boundary(new_len));
+            self.vec.truncate(new_len)
+        }
+    }
+
+    /// Removes the last character from the string buffer and returns it.
+    ///
+    /// Returns [`None`] if this `String` is empty.
+    ///
+    /// [`None`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("foo", &b);
+    ///
+    /// assert_eq!(s.pop(), Some('o'));
+    /// assert_eq!(s.pop(), Some('o'));
+    /// assert_eq!(s.pop(), Some('f'));
+    ///
+    /// assert_eq!(s.pop(), None);
+    /// ```
+    #[inline]
+    pub fn pop(&mut self) -> Option<char> {
+        let ch = self.chars().rev().next()?;
+        let newlen = self.len() - ch.len_utf8();
+        unsafe {
+            self.vec.set_len(newlen);
+        }
+        Some(ch)
+    }
+
+    /// Removes a [`char`] from this `String` at a byte position and returns it.
+    ///
+    /// This is an `O(n)` operation, as it requires copying every element in the
+    /// buffer.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `idx` is larger than or equal to the `String`'s length,
+    /// or if it does not lie on a [`char`] boundary.
+    ///
+    /// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("foo", &b);
+    ///
+    /// assert_eq!(s.remove(0), 'f');
+    /// assert_eq!(s.remove(1), 'o');
+    /// assert_eq!(s.remove(0), 'o');
+    /// ```
+    #[inline]
+    pub fn remove(&mut self, idx: usize) -> char {
+        let ch = match self[idx..].chars().next() {
+            Some(ch) => ch,
+            None => panic!("cannot remove a char from the end of a string"),
+        };
+
+        let next = idx + ch.len_utf8();
+        let len = self.len();
+        unsafe {
+            ptr::copy(
+                self.vec.as_ptr().add(next),
+                self.vec.as_mut_ptr().add(idx),
+                len - next,
+            );
+            self.vec.set_len(len - (next - idx));
+        }
+        ch
+    }
+
+    /// Retains only the characters specified by the predicate.
+    ///
+    /// In other words, remove all characters `c` such that `f(c)` returns `false`.
+    /// This method operates in place and preserves the order of the retained
+    /// characters.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("f_o_ob_ar", &b);
+    ///
+    /// s.retain(|c| c != '_');
+    ///
+    /// assert_eq!(s, "foobar");
+    /// ```
+    #[inline]
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(char) -> bool,
+    {
+        let len = self.len();
+        let mut del_bytes = 0;
+        let mut idx = 0;
+
+        while idx < len {
+            let ch = unsafe { self.get_unchecked(idx..len).chars().next().unwrap() };
+            let ch_len = ch.len_utf8();
+
+            if !f(ch) {
+                del_bytes += ch_len;
+            } else if del_bytes > 0 {
+                unsafe {
+                    ptr::copy(
+                        self.vec.as_ptr().add(idx),
+                        self.vec.as_mut_ptr().add(idx - del_bytes),
+                        ch_len,
+                    );
+                }
+            }
+
+            // Point idx to the next char
+            idx += ch_len;
+        }
+
+        if del_bytes > 0 {
+            unsafe {
+                self.vec.set_len(len - del_bytes);
+            }
+        }
+    }
+
+    /// Inserts a character into this `String` at a byte position.
+    ///
+    /// This is an `O(n)` operation as it requires copying every element in the
+    /// buffer.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `idx` is larger than the `String`'s length, or if it does not
+    /// lie on a [`char`] boundary.
+    ///
+    /// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::with_capacity_in(3, &b);
+    ///
+    /// s.insert(0, 'f');
+    /// s.insert(1, 'o');
+    /// s.insert(2, 'o');
+    ///
+    /// assert_eq!("foo", s);
+    /// ```
+    #[inline]
+    pub fn insert(&mut self, idx: usize, ch: char) {
+        assert!(self.is_char_boundary(idx));
+        let mut bits = [0; 4];
+        let bits = ch.encode_utf8(&mut bits).as_bytes();
+
+        unsafe {
+            self.insert_bytes(idx, bits);
+        }
+    }
+
+    unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
+        let len = self.len();
+        let amt = bytes.len();
+        self.vec.reserve(amt);
+
+        ptr::copy(
+            self.vec.as_ptr().add(idx),
+            self.vec.as_mut_ptr().add(idx + amt),
+            len - idx,
+        );
+        ptr::copy(bytes.as_ptr(), self.vec.as_mut_ptr().add(idx), amt);
+        self.vec.set_len(len + amt);
+    }
+
+    /// Inserts a string slice into this `String` at a byte position.
+    ///
+    /// This is an `O(n)` operation as it requires copying every element in the
+    /// buffer.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `idx` is larger than the `String`'s length, or if it does not
+    /// lie on a [`char`] boundary.
+    ///
+    /// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("bar", &b);
+    ///
+    /// s.insert_str(0, "foo");
+    ///
+    /// assert_eq!("foobar", s);
+    /// ```
+    #[inline]
+    pub fn insert_str(&mut self, idx: usize, string: &str) {
+        assert!(self.is_char_boundary(idx));
+
+        unsafe {
+            self.insert_bytes(idx, string.as_bytes());
+        }
+    }
+
+    /// Returns a mutable reference to the contents of this `String`.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because the returned `&mut Vec` allows writing
+    /// bytes which are not valid UTF-8. If this constraint is violated, using
+    /// the original `String` after dropping the `&mut Vec` may violate memory
+    /// safety, as it is assumed that `String`s are valid UTF-8.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("hello", &b);
+    ///
+    /// unsafe {
+    ///     let vec = s.as_mut_vec();
+    ///     assert_eq!(vec, &[104, 101, 108, 108, 111]);
+    ///
+    ///     vec.reverse();
+    /// }
+    /// assert_eq!(s, "olleh");
+    /// ```
+    #[inline]
+    pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<'bump, u8> {
+        &mut self.vec
+    }
+
+    /// Returns the length of this `String`, in bytes.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let a = String::from_str_in("foo", &b);
+    ///
+    /// assert_eq!(a.len(), 3);
+    /// ```
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.vec.len()
+    }
+
+    /// Returns `true` if this `String` has a length of zero.
+    ///
+    /// Returns `false` otherwise.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = String::new_in(&b);
+    /// assert!(v.is_empty());
+    ///
+    /// v.push('a');
+    /// assert!(!v.is_empty());
+    /// ```
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Splits the string into two at the given index.
+    ///
+    /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
+    /// the returned `String` contains bytes `[at, len)`. `at` must be on the
+    /// boundary of a UTF-8 code point.
+    ///
+    /// Note that the capacity of `self` does not change.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `at` is not on a UTF-8 code point boundary, or if it is beyond the last
+    /// code point of the string.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut hello = String::from_str_in("Hello, World!", &b);
+    /// let world = hello.split_off(7);
+    /// assert_eq!(hello, "Hello, ");
+    /// assert_eq!(world, "World!");
+    /// ```
+    #[inline]
+    pub fn split_off(&mut self, at: usize) -> String<'bump> {
+        assert!(self.is_char_boundary(at));
+        let other = self.vec.split_off(at);
+        unsafe { String::from_utf8_unchecked(other) }
+    }
+
+    /// Truncates this `String`, removing all contents.
+    ///
+    /// While this means the `String` will have a length of zero, it does not
+    /// touch its capacity.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("foo", &b);
+    ///
+    /// s.clear();
+    ///
+    /// assert!(s.is_empty());
+    /// assert_eq!(0, s.len());
+    /// assert_eq!(3, s.capacity());
+    /// ```
+    #[inline]
+    pub fn clear(&mut self) {
+        self.vec.clear()
+    }
+
+    /// Creates a draining iterator that removes the specified range in the `String`
+    /// and yields the removed `chars`.
+    ///
+    /// Note: The element range is removed even if the iterator is not
+    /// consumed until the end.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the starting point or end point do not lie on a [`char`]
+    /// boundary, or if they're out of bounds.
+    ///
+    /// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("α is alpha, β is beta", &b);
+    /// let beta_offset = s.find('β').unwrap_or(s.len());
+    ///
+    /// // Remove the range up until the β from the string
+    /// let t = String::from_iter_in(s.drain(..beta_offset), &b);
+    /// assert_eq!(t, "α is alpha, ");
+    /// assert_eq!(s, "β is beta");
+    ///
+    /// // A full range clears the string
+    /// drop(s.drain(..));
+    /// assert_eq!(s, "");
+    /// ```
+    pub fn drain<'a, R>(&'a mut self, range: R) -> Drain<'a, 'bump>
+    where
+        R: RangeBounds<usize>,
+    {
+        // Memory safety
+        //
+        // The String version of Drain does not have the memory safety issues
+        // of the vector version. The data is just plain bytes.
+        // Because the range removal happens in Drop, if the Drain iterator is leaked,
+        // the removal will not happen.
+        let len = self.len();
+        let start = match range.start_bound() {
+            Included(&n) => n,
+            Excluded(&n) => n + 1,
+            Unbounded => 0,
+        };
+        let end = match range.end_bound() {
+            Included(&n) => n + 1,
+            Excluded(&n) => n,
+            Unbounded => len,
+        };
+
+        // Take out two simultaneous borrows. The &mut String won't be accessed
+        // until iteration is over, in Drop.
+        let self_ptr = self as *mut _;
+        // slicing does the appropriate bounds checks
+        let chars_iter = self[start..end].chars();
+
+        Drain {
+            start,
+            end,
+            iter: chars_iter,
+            string: self_ptr,
+        }
+    }
+
+    /// Removes the specified range in the string,
+    /// and replaces it with the given string.
+    /// The given string doesn't need to be the same length as the range.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the starting point or end point do not lie on a [`char`]
+    /// boundary, or if they're out of bounds.
+    ///
+    /// [`char`]: https://doc.rust-lang.org/std/primitive.char.html
+    /// [`Vec::splice`]: ../vec/struct.Vec.html#method.splice
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut s = String::from_str_in("α is alpha, β is beta", &b);
+    /// let beta_offset = s.find('β').unwrap_or(s.len());
+    ///
+    /// // Replace the range up until the β from the string
+    /// s.replace_range(..beta_offset, "Α is capital alpha; ");
+    /// assert_eq!(s, "Α is capital alpha; β is beta");
+    /// ```
+    pub fn replace_range<R>(&mut self, range: R, replace_with: &str)
+    where
+        R: RangeBounds<usize>,
+    {
+        // Memory safety
+        //
+        // Replace_range does not have the memory safety issues of a vector Splice.
+        // of the vector version. The data is just plain bytes.
+
+        match range.start_bound() {
+            Included(&n) => assert!(self.is_char_boundary(n)),
+            Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
+            Unbounded => {}
+        };
+        match range.end_bound() {
+            Included(&n) => assert!(self.is_char_boundary(n + 1)),
+            Excluded(&n) => assert!(self.is_char_boundary(n)),
+            Unbounded => {}
+        };
+
+        unsafe { self.as_mut_vec() }.splice(range, replace_with.bytes());
+    }
+}
+
+impl<'bump> FromUtf8Error<'bump> {
+    /// Returns a slice of bytes that were attempted to convert to a `String`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some invalid bytes, in a vector
+    /// let bytes = bumpalo::vec![in &b; 0, 159];
+    ///
+    /// let value = String::from_utf8(bytes);
+    ///
+    /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
+    /// ```
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.bytes[..]
+    }
+
+    /// Returns the bytes that were attempted to convert to a `String`.
+    ///
+    /// This method is carefully constructed to avoid allocation. It will
+    /// consume the error, moving out the bytes, so that a copy of the bytes
+    /// does not need to be made.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some invalid bytes, in a vector
+    /// let bytes = bumpalo::vec![in &b; 0, 159];
+    ///
+    /// let value = String::from_utf8(bytes);
+    ///
+    /// assert_eq!(bumpalo::vec![in &b; 0, 159], value.unwrap_err().into_bytes());
+    /// ```
+    pub fn into_bytes(self) -> Vec<'bump, u8> {
+        self.bytes
+    }
+
+    /// Fetch a `Utf8Error` to get more details about the conversion failure.
+    ///
+    /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
+    /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
+    /// an analogue to `FromUtf8Error`. See its documentation for more details
+    /// on using it.
+    ///
+    /// [`Utf8Error`]: https://doc.rust-lang.org/std/str/struct.Utf8Error.html
+    /// [`std::str`]: https://doc.rust-lang.org/std/str/index.html
+    /// [`u8`]: https://doc.rust-lang.org/std/primitive.u8.html
+    /// [`&str`]: https://doc.rust-lang.org/std/primitive.str.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::String};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// // some invalid bytes, in a vector
+    /// let bytes = bumpalo::vec![in &b; 0, 159];
+    ///
+    /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
+    ///
+    /// // the first byte is invalid here
+    /// assert_eq!(1, error.valid_up_to());
+    /// ```
+    pub fn utf8_error(&self) -> Utf8Error {
+        self.error
+    }
+}
+
+impl<'bump> fmt::Display for FromUtf8Error<'bump> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&self.error, f)
+    }
+}
+
+impl fmt::Display for FromUtf16Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
+    }
+}
+
+impl<'bump> Clone for String<'bump> {
+    fn clone(&self) -> Self {
+        String {
+            vec: self.vec.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, source: &Self) {
+        self.vec.clone_from(&source.vec);
+    }
+}
+
+impl<'bump> Extend<char> for String<'bump> {
+    fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
+        let iterator = iter.into_iter();
+        let (lower_bound, _) = iterator.size_hint();
+        self.reserve(lower_bound);
+        for ch in iterator {
+            self.push(ch)
+        }
+    }
+}
+
+impl<'a, 'bump> Extend<&'a char> for String<'bump> {
+    fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().cloned());
+    }
+}
+
+impl<'a, 'bump> Extend<&'a str> for String<'bump> {
+    fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
+        for s in iter {
+            self.push_str(s)
+        }
+    }
+}
+
+impl<'bump> Extend<String<'bump>> for String<'bump> {
+    fn extend<I: IntoIterator<Item = String<'bump>>>(&mut self, iter: I) {
+        for s in iter {
+            self.push_str(&s)
+        }
+    }
+}
+
+impl<'bump> Extend<core_alloc::string::String> for String<'bump> {
+    fn extend<I: IntoIterator<Item = core_alloc::string::String>>(&mut self, iter: I) {
+        for s in iter {
+            self.push_str(&s)
+        }
+    }
+}
+
+impl<'a, 'bump> Extend<Cow<'a, str>> for String<'bump> {
+    fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
+        for s in iter {
+            self.push_str(&s)
+        }
+    }
+}
+
+impl<'bump> PartialEq for String<'bump> {
+    #[inline]
+    fn eq(&self, other: &String) -> bool {
+        PartialEq::eq(&self[..], &other[..])
+    }
+}
+
+macro_rules! impl_eq {
+    ($lhs:ty, $rhs: ty) => {
+        impl<'a, 'bump> PartialEq<$rhs> for $lhs {
+            #[inline]
+            fn eq(&self, other: &$rhs) -> bool {
+                PartialEq::eq(&self[..], &other[..])
+            }
+        }
+
+        impl<'a, 'b, 'bump> PartialEq<$lhs> for $rhs {
+            #[inline]
+            fn eq(&self, other: &$lhs) -> bool {
+                PartialEq::eq(&self[..], &other[..])
+            }
+        }
+    };
+}
+
+impl_eq! { String<'bump>, str }
+impl_eq! { String<'bump>, &'a str }
+impl_eq! { Cow<'a, str>, String<'bump> }
+impl_eq! { core_alloc::string::String, String<'bump> }
+
+impl<'bump> fmt::Display for String<'bump> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<'bump> fmt::Debug for String<'bump> {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'bump> hash::Hash for String<'bump> {
+    #[inline]
+    fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
+        (**self).hash(hasher)
+    }
+}
+
+/// Implements the `+` operator for concatenating two strings.
+///
+/// This consumes the `String<'bump>` on the left-hand side and re-uses its buffer (growing it if
+/// necessary). This is done to avoid allocating a new `String<'bump>` and copying the entire contents on
+/// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
+/// repeated concatenation.
+///
+/// The string on the right-hand side is only borrowed; its contents are copied into the returned
+/// `String<'bump>`.
+///
+/// # Examples
+///
+/// Concatenating two `String<'bump>`s takes the first by value and borrows the second:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let bump = Bump::new();
+///
+/// let a = String::from_str_in("hello", &bump);
+/// let b = String::from_str_in(" world", &bump);
+/// let c = a + &b;
+/// // `a` is moved and can no longer be used here.
+/// ```
+///
+/// If you want to keep using the first `String`, you can clone it and append to the clone instead:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let bump = Bump::new();
+///
+/// let a = String::from_str_in("hello", &bump);
+/// let b = String::from_str_in(" world", &bump);
+/// let c = a.clone() + &b;
+/// // `a` is still valid here.
+/// ```
+///
+/// Concatenating `&str` slices can be done by converting the first to a `String`:
+///
+/// ```
+/// use bumpalo::{Bump, collections::String};
+///
+/// let bump = Bump::new();
+///
+/// let a = "hello";
+/// let b = " world";
+/// let c = String::from_str_in(a, &bump) + b;
+/// ```
+impl<'a, 'bump> Add<&'a str> for String<'bump> {
+    type Output = String<'bump>;
+
+    #[inline]
+    fn add(mut self, other: &str) -> String<'bump> {
+        self.push_str(other);
+        self
+    }
+}
+
+/// Implements the `+=` operator for appending to a `String<'bump>`.
+///
+/// This has the same behavior as the [`push_str`][String::push_str] method.
+impl<'a, 'bump> AddAssign<&'a str> for String<'bump> {
+    #[inline]
+    fn add_assign(&mut self, other: &str) {
+        self.push_str(other);
+    }
+}
+
+impl<'bump> ops::Index<ops::Range<usize>> for String<'bump> {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, index: ops::Range<usize>) -> &str {
+        &self[..][index]
+    }
+}
+impl<'bump> ops::Index<ops::RangeTo<usize>> for String<'bump> {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, index: ops::RangeTo<usize>) -> &str {
+        &self[..][index]
+    }
+}
+impl<'bump> ops::Index<ops::RangeFrom<usize>> for String<'bump> {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, index: ops::RangeFrom<usize>) -> &str {
+        &self[..][index]
+    }
+}
+impl<'bump> ops::Index<ops::RangeFull> for String<'bump> {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, _index: ops::RangeFull) -> &str {
+        unsafe { str::from_utf8_unchecked(&self.vec) }
+    }
+}
+impl<'bump> ops::Index<ops::RangeInclusive<usize>> for String<'bump> {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
+        Index::index(&**self, index)
+    }
+}
+impl<'bump> ops::Index<ops::RangeToInclusive<usize>> for String<'bump> {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
+        Index::index(&**self, index)
+    }
+}
+
+impl<'bump> ops::IndexMut<ops::Range<usize>> for String<'bump> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
+        &mut self[..][index]
+    }
+}
+impl<'bump> ops::IndexMut<ops::RangeTo<usize>> for String<'bump> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
+        &mut self[..][index]
+    }
+}
+impl<'bump> ops::IndexMut<ops::RangeFrom<usize>> for String<'bump> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
+        &mut self[..][index]
+    }
+}
+impl<'bump> ops::IndexMut<ops::RangeFull> for String<'bump> {
+    #[inline]
+    fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
+        unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
+    }
+}
+impl<'bump> ops::IndexMut<ops::RangeInclusive<usize>> for String<'bump> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+impl<'bump> ops::IndexMut<ops::RangeToInclusive<usize>> for String<'bump> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+
+impl<'bump> ops::Deref for String<'bump> {
+    type Target = str;
+
+    #[inline]
+    fn deref(&self) -> &str {
+        unsafe { str::from_utf8_unchecked(&self.vec) }
+    }
+}
+
+impl<'bump> ops::DerefMut for String<'bump> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut str {
+        unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
+    }
+}
+
+impl<'bump> AsRef<str> for String<'bump> {
+    #[inline]
+    fn as_ref(&self) -> &str {
+        self
+    }
+}
+
+impl<'bump> AsRef<[u8]> for String<'bump> {
+    #[inline]
+    fn as_ref(&self) -> &[u8] {
+        self.as_bytes()
+    }
+}
+
+impl<'bump> fmt::Write for String<'bump> {
+    #[inline]
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.push_str(s);
+        Ok(())
+    }
+
+    #[inline]
+    fn write_char(&mut self, c: char) -> fmt::Result {
+        self.push(c);
+        Ok(())
+    }
+}
+
+impl<'bump> Borrow<str> for String<'bump> {
+    #[inline]
+    fn borrow(&self) -> &str {
+        &self[..]
+    }
+}
+
+impl<'bump> BorrowMut<str> for String<'bump> {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut str {
+        &mut self[..]
+    }
+}
+
+/// A draining iterator for `String`.
+///
+/// This struct is created by the [`String::drain`] method. See its
+/// documentation for more information.
+pub struct Drain<'a, 'bump> {
+    /// Will be used as &'a mut String in the destructor
+    string: *mut String<'bump>,
+    /// Start of part to remove
+    start: usize,
+    /// End of part to remove
+    end: usize,
+    /// Current remaining range to remove
+    iter: Chars<'a>,
+}
+
+impl<'a, 'bump> fmt::Debug for Drain<'a, 'bump> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("Drain { .. }")
+    }
+}
+
+unsafe impl<'a, 'bump> Sync for Drain<'a, 'bump> {}
+unsafe impl<'a, 'bump> Send for Drain<'a, 'bump> {}
+
+impl<'a, 'bump> Drop for Drain<'a, 'bump> {
+    fn drop(&mut self) {
+        unsafe {
+            // Use Vec::drain. "Reaffirm" the bounds checks to avoid
+            // panic code being inserted again.
+            let self_vec = (*self.string).as_mut_vec();
+            if self.start <= self.end && self.end <= self_vec.len() {
+                self_vec.drain(self.start..self.end);
+            }
+        }
+    }
+}
+
+// TODO: implement `AsRef<str/[u8]>` and `as_str`
+
+impl<'a, 'bump> Iterator for Drain<'a, 'bump> {
+    type Item = char;
+
+    #[inline]
+    fn next(&mut self) -> Option<char> {
+        self.iter.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<'a, 'bump> DoubleEndedIterator for Drain<'a, 'bump> {
+    #[inline]
+    fn next_back(&mut self) -> Option<char> {
+        self.iter.next_back()
+    }
+}
+
+impl<'a, 'bump> FusedIterator for Drain<'a, 'bump> {}
diff --git a/third_party/rust/bumpalo/src/collections/vec.rs b/third_party/rust/bumpalo/src/collections/vec.rs
new file mode 100644
index 0000000000..b5a60029ef
--- /dev/null
+++ b/third_party/rust/bumpalo/src/collections/vec.rs
@@ -0,0 +1,2594 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A contiguous growable array type with heap-allocated contents, written
+//! [`Vec<'bump, T>`].
+//!
+//! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
+//! `O(1)` pop (from the end).
+//!
+//! This module is a fork of the [`std::vec`] module, that uses a bump allocator.
+//!
+//! [`std::vec`]: https://doc.rust-lang.org/std/vec/index.html
+//!
+//! # Examples
+//!
+//! You can explicitly create a [`Vec<'bump, T>`] with [`new_in`]:
+//!
+//! ```
+//! use bumpalo::{Bump, collections::Vec};
+//!
+//! let b = Bump::new();
+//! let v: Vec<i32> = Vec::new_in(&b);
+//! ```
+//!
+//! ... or by using the [`vec!`] macro:
+//!
+//! ```
+//! use bumpalo::{Bump, collections::Vec};
+//!
+//! let b = Bump::new();
+//!
+//! let v: Vec<i32> = bumpalo::vec![in &b];
+//!
+//! let v = bumpalo::vec![in &b; 1, 2, 3, 4, 5];
+//!
+//! let v = bumpalo::vec![in &b; 0; 10]; // ten zeroes
+//! ```
+//!
+//! You can [`push`] values onto the end of a vector (which will grow the vector
+//! as needed):
+//!
+//! ```
+//! use bumpalo::{Bump, collections::Vec};
+//!
+//! let b = Bump::new();
+//!
+//! let mut v = bumpalo::vec![in &b; 1, 2];
+//!
+//! v.push(3);
+//! ```
+//!
+//! Popping values works in much the same way:
+//!
+//! ```
+//! use bumpalo::{Bump, collections::Vec};
+//!
+//! let b = Bump::new();
+//!
+//! let mut v = bumpalo::vec![in &b; 1, 2];
+//!
+//! assert_eq!(v.pop(), Some(2));
+//! ```
+//!
+//! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
+//!
+//! ```
+//! use bumpalo::{Bump, collections::Vec};
+//!
+//! let b = Bump::new();
+//!
+//! let mut v = bumpalo::vec![in &b; 1, 2, 3];
+//! assert_eq!(v[2], 3);
+//! v[1] += 5;
+//! assert_eq!(v, [1, 7, 3]);
+//! ```
+//!
+//! [`Vec<'bump, T>`]: struct.Vec.html
+//! [`new_in`]: struct.Vec.html#method.new_in
+//! [`push`]: struct.Vec.html#method.push
+//! [`Index`]: https://doc.rust-lang.org/std/ops/trait.Index.html
+//! [`IndexMut`]: https://doc.rust-lang.org/std/ops/trait.IndexMut.html
+//! [`vec!`]: ../../macro.vec.html
+
+use super::raw_vec::RawVec;
+use crate::collections::CollectionAllocErr;
+use crate::Bump;
+use core::borrow::{Borrow, BorrowMut};
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{self, Hash};
+use core::iter::FusedIterator;
+use core::marker::PhantomData;
+use core::mem;
+use core::ops;
+use core::ops::Bound::{Excluded, Included, Unbounded};
+use core::ops::{Index, IndexMut, RangeBounds};
+use core::ptr;
+use core::ptr::NonNull;
+use core::slice;
+
+unsafe fn arith_offset<T>(p: *const T, offset: isize) -> *const T {
+    p.offset(offset)
+}
+
+fn partition_dedup_by<T, F>(s: &mut [T], mut same_bucket: F) -> (&mut [T], &mut [T])
+where
+    F: FnMut(&mut T, &mut T) -> bool,
+{
+    // Although we have a mutable reference to `s`, we cannot make
+    // *arbitrary* changes. The `same_bucket` calls could panic, so we
+    // must ensure that the slice is in a valid state at all times.
+    //
+    // The way that we handle this is by using swaps; we iterate
+    // over all the elements, swapping as we go so that at the end
+    // the elements we wish to keep are in the front, and those we
+    // wish to reject are at the back. We can then split the slice.
+    // This operation is still O(n).
+    //
+    // Example: We start in this state, where `r` represents "next
+    // read" and `w` represents "next_write`.
+    //
+    //           r
+    //     +---+---+---+---+---+---+
+    //     | 0 | 1 | 1 | 2 | 3 | 3 |
+    //     +---+---+---+---+---+---+
+    //           w
+    //
+    // Comparing s[r] against s[w-1], this is not a duplicate, so
+    // we swap s[r] and s[w] (no effect as r==w) and then increment both
+    // r and w, leaving us with:
+    //
+    //               r
+    //     +---+---+---+---+---+---+
+    //     | 0 | 1 | 1 | 2 | 3 | 3 |
+    //     +---+---+---+---+---+---+
+    //               w
+    //
+    // Comparing s[r] against s[w-1], this value is a duplicate,
+    // so we increment `r` but leave everything else unchanged:
+    //
+    //                   r
+    //     +---+---+---+---+---+---+
+    //     | 0 | 1 | 1 | 2 | 3 | 3 |
+    //     +---+---+---+---+---+---+
+    //               w
+    //
+    // Comparing s[r] against s[w-1], this is not a duplicate,
+    // so swap s[r] and s[w] and advance r and w:
+    //
+    //                       r
+    //     +---+---+---+---+---+---+
+    //     | 0 | 1 | 2 | 1 | 3 | 3 |
+    //     +---+---+---+---+---+---+
+    //                   w
+    //
+    // Not a duplicate, repeat:
+    //
+    //                           r
+    //     +---+---+---+---+---+---+
+    //     | 0 | 1 | 2 | 3 | 1 | 3 |
+    //     +---+---+---+---+---+---+
+    //                       w
+    //
+    // Duplicate, advance r. End of slice. Split at w.
+
+    let len = s.len();
+    if len <= 1 {
+        return (s, &mut []);
+    }
+
+    let ptr = s.as_mut_ptr();
+    let mut next_read: usize = 1;
+    let mut next_write: usize = 1;
+
+    unsafe {
+        // Avoid bounds checks by using raw pointers.
+        while next_read < len {
+            let ptr_read = ptr.add(next_read);
+            let prev_ptr_write = ptr.add(next_write - 1);
+            if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
+                if next_read != next_write {
+                    let ptr_write = prev_ptr_write.offset(1);
+                    mem::swap(&mut *ptr_read, &mut *ptr_write);
+                }
+                next_write += 1;
+            }
+            next_read += 1;
+        }
+    }
+
+    s.split_at_mut(next_write)
+}
+
+unsafe fn offset_from<T>(p: *const T, origin: *const T) -> isize
+where
+    T: Sized,
+{
+    let pointee_size = mem::size_of::<T>();
+    assert!(0 < pointee_size && pointee_size <= isize::max_value() as usize);
+
+    // This is the same sequence that Clang emits for pointer subtraction.
+    // It can be neither `nsw` nor `nuw` because the input is treated as
+    // unsigned but then the output is treated as signed, so neither works.
+    let d = isize::wrapping_sub(p as _, origin as _);
+    d / (pointee_size as isize)
+}
+
+/// Creates a [`Vec`] containing the arguments.
+///
+/// `vec!` allows `Vec`s to be defined with the same syntax as array expressions.
+/// There are two forms of this macro:
+///
+/// - Create a [`Vec`] containing a given list of elements:
+///
+/// ```
+/// use bumpalo::Bump;
+///
+/// let b = Bump::new();
+/// let v = bumpalo::vec![in &b; 1, 2, 3];
+/// assert_eq!(v, [1, 2, 3]);
+/// ```
+///
+/// - Create a [`Vec`] from a given element and size:
+///
+/// ```
+/// use bumpalo::Bump;
+///
+/// let b = Bump::new();
+/// let v = bumpalo::vec![in &b; 1; 3];
+/// assert_eq!(v, [1, 1, 1]);
+/// ```
+///
+/// Note that unlike array expressions, this syntax supports all elements
+/// which implement [`Clone`] and the number of elements doesn't have to be
+/// a constant.
+///
+/// This will use `clone` to duplicate an expression, so one should be careful
+/// using this with types having a non-standard `Clone` implementation. For
+/// example, `bumpalo::vec![in &bump; Rc::new(1); 5]` will create a vector of five references
+/// to the same boxed integer value, not five references pointing to independently
+/// boxed integers.
+///
+/// [`Vec`]: collections/vec/struct.Vec.html
+/// [`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html
+#[macro_export]
+macro_rules! vec {
+    (in $bump:expr; $elem:expr; $n:expr) => {{
+        let n = $n;
+        let mut v = $crate::collections::Vec::with_capacity_in(n, $bump);
+        if n > 0 {
+            let elem = $elem;
+            for _ in 0..n - 1 {
+                v.push(elem.clone());
+            }
+            v.push(elem);
+        }
+        v
+    }};
+    (in $bump:expr) => { $crate::collections::Vec::new_in($bump) };
+    (in $bump:expr; $($x:expr),*) => {{
+        let mut v = $crate::collections::Vec::new_in($bump);
+        $( v.push($x); )*
+        v
+    }};
+    (in $bump:expr; $($x:expr,)*) => (bumpalo::vec![in $bump; $($x),*])
+}
+
+/// A contiguous growable array type, written `Vec<'bump, T>` but pronounced 'vector'.
+///
+/// # Examples
+///
+/// ```
+/// use bumpalo::{Bump, collections::Vec};
+///
+/// let b = Bump::new();
+///
+/// let mut vec = Vec::new_in(&b);
+/// vec.push(1);
+/// vec.push(2);
+///
+/// assert_eq!(vec.len(), 2);
+/// assert_eq!(vec[0], 1);
+///
+/// assert_eq!(vec.pop(), Some(2));
+/// assert_eq!(vec.len(), 1);
+///
+/// vec[0] = 7;
+/// assert_eq!(vec[0], 7);
+///
+/// vec.extend([1, 2, 3].iter().cloned());
+///
+/// for x in &vec {
+///     println!("{}", x);
+/// }
+/// assert_eq!(vec, [7, 1, 2, 3]);
+/// ```
+///
+/// The [`vec!`] macro is provided to make initialization more convenient:
+///
+/// ```
+/// use bumpalo::{Bump, collections::Vec};
+///
+/// let b = Bump::new();
+///
+/// let mut vec = bumpalo::vec![in &b; 1, 2, 3];
+/// vec.push(4);
+/// assert_eq!(vec, [1, 2, 3, 4]);
+/// ```
+///
+/// It can also initialize each element of a `Vec<'bump, T>` with a given value.
+/// This may be more efficient than performing allocation and initialization
+/// in separate steps, especially when initializing a vector of zeros:
+///
+/// ```
+/// use bumpalo::{Bump, collections::Vec};
+///
+/// let b = Bump::new();
+///
+/// let vec = bumpalo::vec![in &b; 0; 5];
+/// assert_eq!(vec, [0, 0, 0, 0, 0]);
+///
+/// // The following is equivalent, but potentially slower:
+/// let mut vec1 = Vec::with_capacity_in(5, &b);
+/// vec1.resize(5, 0);
+/// ```
+///
+/// Use a `Vec<'bump, T>` as an efficient stack:
+///
+/// ```
+/// use bumpalo::{Bump, collections::Vec};
+///
+/// let b = Bump::new();
+///
+/// let mut stack = Vec::new_in(&b);
+///
+/// stack.push(1);
+/// stack.push(2);
+/// stack.push(3);
+///
+/// while let Some(top) = stack.pop() {
+///     // Prints 3, 2, 1
+///     println!("{}", top);
+/// }
+/// ```
+///
+/// # Indexing
+///
+/// The `Vec` type allows to access values by index, because it implements the
+/// [`Index`] trait. An example will be more explicit:
+///
+/// ```
+/// use bumpalo::{Bump, collections::Vec};
+///
+/// let b = Bump::new();
+///
+/// let v = bumpalo::vec![in &b; 0, 2, 4, 6];
+/// println!("{}", v[1]); // it will display '2'
+/// ```
+///
+/// However be careful: if you try to access an index which isn't in the `Vec`,
+/// your software will panic! You cannot do this:
+///
+/// ```should_panic
+/// use bumpalo::{Bump, collections::Vec};
+///
+/// let b = Bump::new();
+///
+/// let v = bumpalo::vec![in &b; 0, 2, 4, 6];
+/// println!("{}", v[6]); // it will panic!
+/// ```
+///
+/// In conclusion: always check if the index you want to get really exists
+/// before doing it.
+///
+/// # Slicing
+///
+/// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
+/// To get a slice, use `&`. Example:
+///
+/// ```
+/// use bumpalo::{Bump, collections::Vec};
+///
+/// fn read_slice(slice: &[usize]) {
+///     // ...
+/// }
+///
+/// let b = Bump::new();
+///
+/// let v = bumpalo::vec![in &b; 0, 1];
+/// read_slice(&v);
+///
+/// // ... and that's all!
+/// // you can also do it like this:
+/// let x : &[usize] = &v;
+/// ```
+///
+/// In Rust, it's more common to pass slices as arguments rather than vectors
+/// when you just want to provide a read access. The same goes for [`String`] and
+/// [`&str`].
+///
+/// # Capacity and reallocation
+///
+/// The capacity of a vector is the amount of space allocated for any future
+/// elements that will be added onto the vector. This is not to be confused with
+/// the *length* of a vector, which specifies the number of actual elements
+/// within the vector. If a vector's length exceeds its capacity, its capacity
+/// will automatically be increased, but its elements will have to be
+/// reallocated.
+///
+/// For example, a vector with capacity 10 and length 0 would be an empty vector
+/// with space for 10 more elements. Pushing 10 or fewer elements onto the
+/// vector will not change its capacity or cause reallocation to occur. However,
+/// if the vector's length is increased to 11, it will have to reallocate, which
+/// can be slow. For this reason, it is recommended to use [`Vec::with_capacity_in`]
+/// whenever possible to specify how big the vector is expected to get.
+///
+/// # Guarantees
+///
+/// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
+/// about its design. This ensures that it's as low-overhead as possible in
+/// the general case, and can be correctly manipulated in primitive ways
+/// by unsafe code. Note that these guarantees refer to an unqualified `Vec<'bump, T>`.
+/// If additional type parameters are added (e.g. to support custom allocators),
+/// overriding their defaults may change the behavior.
+///
+/// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
+/// triplet. No more, no less. The order of these fields is completely
+/// unspecified, and you should use the appropriate methods to modify these.
+/// The pointer will never be null, so this type is null-pointer-optimized.
+///
+/// However, the pointer may not actually point to allocated memory. In particular,
+/// if you construct a `Vec` with capacity 0 via [`Vec::new_in`], [`bumpalo::vec![in bump]`][`vec!`],
+/// [`Vec::with_capacity_in(0)`][`Vec::with_capacity_in`], or by calling [`shrink_to_fit`]
+/// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
+/// types inside a `Vec`, it will not allocate space for them. *Note that in this case
+/// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
+/// if <code>[`mem::size_of::<T>`]\() * capacity() > 0</code>. In general, `Vec`'s allocation
+/// details are very subtle &mdash; if you intend to allocate memory using a `Vec`
+/// and use it for something else (either to pass to unsafe code, or to build your
+/// own memory-backed collection), be sure to deallocate this memory by using
+/// `from_raw_parts` to recover the `Vec` and then dropping it.
+///
+/// If a `Vec` *has* allocated memory, then the memory it points to is
+/// in the [`Bump`] arena used to construct it, and its
+/// pointer points to [`len`] initialized, contiguous elements in order (what
+/// you would see if you coerced it to a slice), followed by <code>[`capacity`] -
+/// [`len`]</code> logically uninitialized, contiguous elements.
+///
+/// `Vec` will never perform a "small optimization" where elements are actually
+/// stored on the stack for two reasons:
+///
+/// * It would make it more difficult for unsafe code to correctly manipulate
+///   a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
+///   only moved, and it would be more difficult to determine if a `Vec` had
+///   actually allocated memory.
+///
+/// * It would penalize the general case, incurring an additional branch
+///   on every access.
+///
+/// `Vec` will never automatically shrink itself, even if completely empty. This
+/// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
+/// and then filling it back up to the same [`len`] should incur no calls to
+/// the allocator. If you wish to free up unused memory, use
+/// [`shrink_to_fit`][`shrink_to_fit`].
+///
+/// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
+/// sufficient. [`push`] and [`insert`] *will* (re)allocate if
+/// <code>[`len`] == [`capacity`]</code>. That is, the reported capacity is completely
+/// accurate, and can be relied on. It can even be used to manually free the memory
+/// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
+/// when not necessary.
+///
+/// `Vec` does not guarantee any particular growth strategy when reallocating
+/// when full, nor when [`reserve`] is called. The current strategy is basic
+/// and it may prove desirable to use a non-constant growth factor. Whatever
+/// strategy is used will of course guarantee `O(1)` amortized [`push`].
+///
+/// `bumpalo::vec![in bump; x; n]`, `bumpalo::vec![in bump; a, b, c, d]`, and
+/// [`Vec::with_capacity_in(n)`][`Vec::with_capacity_in`], will all produce a
+/// `Vec` with exactly the requested capacity. If <code>[`len`] == [`capacity`]</code>, (as
+/// is the case for the [`vec!`] macro), then a `Vec<'bump, T>` can be converted
+/// to and from a [`Box<[T]>`][owned slice] without reallocating or moving the
+/// elements.
+///
+/// `Vec` will not specifically overwrite any data that is removed from it,
+/// but also won't specifically preserve it. Its uninitialized memory is
+/// scratch space that it may use however it wants. It will generally just do
+/// whatever is most efficient or otherwise easy to implement. Do not rely on
+/// removed data to be erased for security purposes. Even if you drop a `Vec`, its
+/// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
+/// first, that may not actually happen because the optimizer does not consider
+/// this a side-effect that must be preserved. There is one case which we will
+/// not break, however: using `unsafe` code to write to the excess capacity,
+/// and then increasing the length to match, is always valid.
+///
+/// `Vec` does not currently guarantee the order in which elements are dropped.
+/// The order has changed in the past and may change again.
+///
+/// [`vec!`]: ../../macro.vec.html
+/// [`Index`]: https://doc.rust-lang.org/std/ops/trait.Index.html
+/// [`String`]: ../string/struct.String.html
+/// [`&str`]: https://doc.rust-lang.org/std/primitive.str.html
+/// [`Vec::with_capacity_in`]: struct.Vec.html#method.with_capacity_in
+/// [`Vec::new_in`]: struct.Vec.html#method.new_in
+/// [`shrink_to_fit`]: struct.Vec.html#method.shrink_to_fit
+/// [`capacity`]: struct.Vec.html#method.capacity
+/// [`mem::size_of::<T>`]: https://doc.rust-lang.org/std/mem/fn.size_of.html
+/// [`len`]: struct.Vec.html#method.len
+/// [`push`]: struct.Vec.html#method.push
+/// [`insert`]: struct.Vec.html#method.insert
+/// [`reserve`]: struct.Vec.html#method.reserve
+/// [owned slice]: https://doc.rust-lang.org/std/boxed/struct.Box.html
+pub struct Vec<'bump, T: 'bump> {
+    buf: RawVec<'bump, T>,
+    len: usize,
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Inherent methods
+////////////////////////////////////////////////////////////////////////////////
+
+impl<'bump, T: 'bump> Vec<'bump, T> {
+    /// Constructs a new, empty `Vec<'bump, T>`.
+    ///
+    /// The vector will not allocate until elements are pushed onto it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(unused_mut)]
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let mut vec: Vec<i32> = Vec::new_in(&b);
+    /// ```
+    #[inline]
+    pub fn new_in(bump: &'bump Bump) -> Vec<'bump, T> {
+        Vec {
+            buf: RawVec::new_in(bump),
+            len: 0,
+        }
+    }
+
+    /// Constructs a new, empty `Vec<'bump, T>` with the specified capacity.
+    ///
+    /// The vector will be able to hold exactly `capacity` elements without
+    /// reallocating. If `capacity` is 0, the vector will not allocate.
+    ///
+    /// It is important to note that although the returned vector has the
+    /// *capacity* specified, the vector will have a zero *length*. For an
+    /// explanation of the difference between length and capacity, see
+    /// *[Capacity and reallocation]*.
+    ///
+    /// [Capacity and reallocation]: #capacity-and-reallocation
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = Vec::with_capacity_in(10, &b);
+    ///
+    /// // The vector contains no items, even though it has capacity for more
+    /// assert_eq!(vec.len(), 0);
+    ///
+    /// // These are all done without reallocating...
+    /// for i in 0..10 {
+    ///     vec.push(i);
+    /// }
+    ///
+    /// // ...but this may make the vector reallocate
+    /// vec.push(11);
+    /// ```
+    #[inline]
+    pub fn with_capacity_in(capacity: usize, bump: &'bump Bump) -> Vec<'bump, T> {
+        Vec {
+            buf: RawVec::with_capacity_in(capacity, bump),
+            len: 0,
+        }
+    }
+
+    /// Construct a new `Vec` from the given iterator's items.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    /// use std::iter;
+    ///
+    /// let b = Bump::new();
+    /// let v = Vec::from_iter_in(iter::repeat(7).take(3), &b);
+    /// assert_eq!(v, [7, 7, 7]);
+    /// ```
+    pub fn from_iter_in<I: IntoIterator<Item = T>>(iter: I, bump: &'bump Bump) -> Vec<'bump, T> {
+        let mut v = Vec::new_in(bump);
+        v.extend(iter);
+        v
+    }
+
+    /// Creates a `Vec<'bump, T>` directly from the raw components of another vector.
+    ///
+    /// # Safety
+    ///
+    /// This is highly unsafe, due to the number of invariants that aren't
+    /// checked:
+    ///
+    /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<'bump, T>`
+    ///   (at least, it's highly likely to be incorrect if it wasn't).
+    /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
+    /// * `length` needs to be less than or equal to `capacity`.
+    /// * `capacity` needs to be the capacity that the pointer was allocated with.
+    ///
+    /// Violating these may cause problems like corrupting the allocator's
+    /// internal data structures. For example it is **not** safe
+    /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
+    ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `Vec<'bump, T>` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
+    /// [`String`]: ../string/struct.String.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// use std::ptr;
+    /// use std::mem;
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = bumpalo::vec![in &b; 1, 2, 3];
+    ///
+    /// // Pull out the various important pieces of information about `v`
+    /// let p = v.as_mut_ptr();
+    /// let len = v.len();
+    /// let cap = v.capacity();
+    ///
+    /// unsafe {
+    ///     // Cast `v` into the void: no destructor run, so we are in
+    ///     // complete control of the allocation to which `p` points.
+    ///     mem::forget(v);
+    ///
+    ///     // Overwrite memory with 4, 5, 6
+    ///     for i in 0..len as isize {
+    ///         ptr::write(p.offset(i), 4 + i);
+    ///     }
+    ///
+    ///     // Put everything back together into a Vec
+    ///     let rebuilt = Vec::from_raw_parts_in(p, len, cap, &b);
+    ///     assert_eq!(rebuilt, [4, 5, 6]);
+    /// }
+    /// ```
+    pub unsafe fn from_raw_parts_in(
+        ptr: *mut T,
+        length: usize,
+        capacity: usize,
+        bump: &'bump Bump,
+    ) -> Vec<'bump, T> {
+        Vec {
+            buf: RawVec::from_raw_parts_in(ptr, capacity, bump),
+            len: length,
+        }
+    }
+
+    /// Returns the number of elements the vector can hold without
+    /// reallocating.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let vec: Vec<i32> = Vec::with_capacity_in(10, &b);
+    /// assert_eq!(vec.capacity(), 10);
+    /// ```
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        self.buf.cap()
+    }
+
+    /// Reserves capacity for at least `additional` more elements to be inserted
+    /// in the given `Vec<'bump, T>`. The collection may reserve more space to avoid
+    /// frequent reallocations. After calling `reserve`, capacity will be
+    /// greater than or equal to `self.len() + additional`. Does nothing if
+    /// capacity is already sufficient.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let mut vec = bumpalo::vec![in &b; 1];
+    /// vec.reserve(10);
+    /// assert!(vec.capacity() >= 11);
+    /// ```
+    pub fn reserve(&mut self, additional: usize) {
+        self.buf.reserve(self.len, additional);
+    }
+
+    /// Reserves the minimum capacity for exactly `additional` more elements to
+    /// be inserted in the given `Vec<'bump, T>`. After calling `reserve_exact`,
+    /// capacity will be greater than or equal to `self.len() + additional`.
+    /// Does nothing if the capacity is already sufficient.
+    ///
+    /// Note that the allocator may give the collection more space than it
+    /// requests. Therefore capacity can not be relied upon to be precisely
+    /// minimal. Prefer `reserve` if future insertions are expected.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let mut vec = bumpalo::vec![in &b; 1];
+    /// vec.reserve_exact(10);
+    /// assert!(vec.capacity() >= 11);
+    /// ```
+    pub fn reserve_exact(&mut self, additional: usize) {
+        self.buf.reserve_exact(self.len, additional);
+    }
+
+    /// Attempts to reserve capacity for at least `additional` more elements to be inserted
+    /// in the given `Vec<'bump, T>`. The collection may reserve more space to avoid
+    /// frequent reallocations. After calling `try_reserve`, capacity will be
+    /// greater than or equal to `self.len() + additional`. Does nothing if
+    /// capacity is already sufficient.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let mut vec = bumpalo::vec![in &b; 1];
+    /// vec.try_reserve(10).unwrap();
+    /// assert!(vec.capacity() >= 11);
+    /// ```
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
+        self.buf.try_reserve(self.len, additional)
+    }
+
+    /// Attempts to reserve the minimum capacity for exactly `additional` more elements to
+    /// be inserted in the given `Vec<'bump, T>`. After calling `try_reserve_exact`,
+    /// capacity will be greater than or equal to `self.len() + additional`.
+    /// Does nothing if the capacity is already sufficient.
+    ///
+    /// Note that the allocator may give the collection more space than it
+    /// requests. Therefore capacity can not be relied upon to be precisely
+    /// minimal. Prefer `try_reserve` if future insertions are expected.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let mut vec = bumpalo::vec![in &b; 1];
+    /// vec.try_reserve_exact(10).unwrap();
+    /// assert!(vec.capacity() >= 11);
+    /// ```
+    pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> {
+        self.buf.try_reserve_exact(self.len, additional)
+    }
+
+    /// Shrinks the capacity of the vector as much as possible.
+    ///
+    /// It will drop down as close as possible to the length but the allocator
+    /// may still inform the vector that there is space for a few more elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = Vec::with_capacity_in(10, &b);
+    /// vec.extend([1, 2, 3].iter().cloned());
+    /// assert_eq!(vec.capacity(), 10);
+    /// vec.shrink_to_fit();
+    /// assert!(vec.capacity() >= 3);
+    /// ```
+    pub fn shrink_to_fit(&mut self) {
+        if self.capacity() != self.len {
+            self.buf.shrink_to_fit(self.len);
+        }
+    }
+
+    /// Converts the vector into `&'bump [T]`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let v = bumpalo::vec![in &b; 1, 2, 3];
+    ///
+    /// let slice = v.into_bump_slice();
+    /// assert_eq!(slice, [1, 2, 3]);
+    /// ```
+    pub fn into_bump_slice(self) -> &'bump [T] {
+        unsafe {
+            let ptr = self.as_ptr();
+            let len = self.len();
+            mem::forget(self);
+            slice::from_raw_parts(ptr, len)
+        }
+    }
+
+    /// Converts the vector into `&'bump mut [T]`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    /// let v = bumpalo::vec![in &b; 1, 2, 3];
+    ///
+    /// let mut slice = v.into_bump_slice_mut();
+    ///
+    /// slice[0] = 3;
+    /// slice[2] = 1;
+    ///
+    /// assert_eq!(slice, [3, 2, 1]);
+    /// ```
+    pub fn into_bump_slice_mut(mut self) -> &'bump mut [T] {
+        let ptr = self.as_mut_ptr();
+        let len = self.len();
+        mem::forget(self);
+
+        unsafe { slice::from_raw_parts_mut(ptr, len) }
+    }
+
+    /// Shortens the vector, keeping the first `len` elements and dropping
+    /// the rest.
+    ///
+    /// If `len` is greater than the vector's current length, this has no
+    /// effect.
+    ///
+    /// The [`drain`] method can emulate `truncate`, but causes the excess
+    /// elements to be returned instead of dropped.
+    ///
+    /// Note that this method has no effect on the allocated capacity
+    /// of the vector.
+    ///
+    /// # Examples
+    ///
+    /// Truncating a five element vector to two elements:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3, 4, 5];
+    /// vec.truncate(2);
+    /// assert_eq!(vec, [1, 2]);
+    /// ```
+    ///
+    /// No truncation occurs when `len` is greater than the vector's current
+    /// length:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3];
+    /// vec.truncate(8);
+    /// assert_eq!(vec, [1, 2, 3]);
+    /// ```
+    ///
+    /// Truncating when `len == 0` is equivalent to calling the [`clear`]
+    /// method.
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3];
+    /// vec.truncate(0);
+    /// assert_eq!(vec, []);
+    /// ```
+    ///
+    /// [`clear`]: #method.clear
+    /// [`drain`]: #method.drain
+    pub fn truncate(&mut self, len: usize) {
+        let current_len = self.len;
+        unsafe {
+            let mut ptr = self.as_mut_ptr().add(self.len);
+            // Set the final length at the end, keeping in mind that
+            // dropping an element might panic. Works around a missed
+            // optimization, as seen in the following issue:
+            // https://github.com/rust-lang/rust/issues/51802
+            let mut local_len = SetLenOnDrop::new(&mut self.len);
+
+            // drop any extra elements
+            for _ in len..current_len {
+                local_len.decrement_len(1);
+                ptr = ptr.offset(-1);
+                ptr::drop_in_place(ptr);
+            }
+        }
+    }
+
+    /// Extracts a slice containing the entire vector.
+    ///
+    /// Equivalent to `&s[..]`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    /// use std::io::{self, Write};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let buffer = bumpalo::vec![in &b; 1, 2, 3, 5, 8];
+    /// io::sink().write(buffer.as_slice()).unwrap();
+    /// ```
+    #[inline]
+    pub fn as_slice(&self) -> &[T] {
+        self
+    }
+
+    /// Extracts a mutable slice of the entire vector.
+    ///
+    /// Equivalent to `&mut s[..]`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    /// use std::io::{self, Read};
+    ///
+    /// let b = Bump::new();
+    /// let mut buffer = bumpalo::vec![in &b; 0; 3];
+    /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
+    /// ```
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        self
+    }
+
+    /// Returns a raw pointer to the vector's buffer, or a dangling raw pointer
+    /// valid for zero sized reads if the vector didn't allocate.
+    ///
+    /// The caller must ensure that the vector outlives the pointer this
+    /// function returns, or else it will end up pointing to garbage.
+    /// Modifying the vector may cause its buffer to be reallocated,
+    /// which would also make any pointers to it invalid.
+    ///
+    /// The caller must also ensure that the memory the pointer (non-transitively) points to
+    /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer
+    /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let bump = Bump::new();
+    ///
+    /// let x = bumpalo::vec![in &bump; 1, 2, 4];
+    /// let x_ptr = x.as_ptr();
+    ///
+    /// unsafe {
+    ///     for i in 0..x.len() {
+    ///         assert_eq!(*x_ptr.add(i), 1 << i);
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`as_mut_ptr`]: Vec::as_mut_ptr
+    #[inline]
+    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 {
+            if ptr.is_null() {
+                core::hint::unreachable_unchecked();
+            }
+        }
+        ptr
+    }
+
+    /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
+    /// raw pointer valid for zero sized reads if the vector didn't allocate.
+    ///
+    /// The caller must ensure that the vector outlives the pointer this
+    /// function returns, or else it will end up pointing to garbage.
+    /// Modifying the vector may cause its buffer to be reallocated,
+    /// which would also make any pointers to it invalid.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let bump = Bump::new();
+    ///
+    /// // Allocate vector big enough for 4 elements.
+    /// let size = 4;
+    /// let mut x: Vec<i32> = Vec::with_capacity_in(size, &bump);
+    /// let x_ptr = x.as_mut_ptr();
+    ///
+    /// // Initialize elements via raw pointer writes, then set length.
+    /// unsafe {
+    ///     for i in 0..size {
+    ///         x_ptr.add(i).write(i as i32);
+    ///     }
+    ///     x.set_len(size);
+    /// }
+    /// assert_eq!(&*x, &[0, 1, 2, 3]);
+    /// ```
+    #[inline]
+    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 {
+            if ptr.is_null() {
+                core::hint::unreachable_unchecked();
+            }
+        }
+        ptr
+    }
+
+    /// Sets the length of a vector.
+    ///
+    /// This will explicitly set the size of the vector, without actually
+    /// modifying its buffers, so it is up to the caller to ensure that the
+    /// vector is actually the specified size.
+    ///
+    /// # Safety
+    ///
+    /// - `new_len` must be less than or equal to [`capacity()`].
+    /// - The elements at `old_len..new_len` must be initialized.
+    ///
+    /// [`capacity()`]: struct.Vec.html#method.capacity
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// use std::ptr;
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 'r', 'u', 's', 't'];
+    ///
+    /// unsafe {
+    ///     ptr::drop_in_place(&mut vec[3]);
+    ///     vec.set_len(3);
+    /// }
+    /// assert_eq!(vec, ['r', 'u', 's']);
+    /// ```
+    ///
+    /// In this example, there is a memory leak since the memory locations
+    /// owned by the inner vectors were not freed prior to the `set_len` call:
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b;
+    ///                             bumpalo::vec![in &b; 1, 0, 0],
+    ///                             bumpalo::vec![in &b; 0, 1, 0],
+    ///                             bumpalo::vec![in &b; 0, 0, 1]];
+    /// unsafe {
+    ///     vec.set_len(0);
+    /// }
+    /// ```
+    ///
+    /// In this example, the vector gets expanded from zero to four items
+    /// but we directly initialize uninitialized memory:
+    ///
+    // TODO: rely upon `spare_capacity_mut`
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let len = 4;
+    /// let b = Bump::new();
+    ///
+    /// let mut vec: Vec<u8> = Vec::with_capacity_in(len, &b);
+    ///
+    /// for i in 0..len {
+    ///     // SAFETY: we initialize memory via `pointer::write`
+    ///     unsafe { vec.as_mut_ptr().add(i).write(b'a') }
+    /// }
+    ///
+    /// unsafe {
+    ///     vec.set_len(len);
+    /// }
+    ///
+    /// assert_eq!(b"aaaa", &*vec);
+    /// ```
+    #[inline]
+    pub unsafe fn set_len(&mut self, new_len: usize) {
+        self.len = new_len;
+    }
+
+    /// Removes an element from the vector and returns it.
+    ///
+    /// The removed element is replaced by the last element of the vector.
+    ///
+    /// This does not preserve ordering, but is O(1).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = bumpalo::vec![in &b; "foo", "bar", "baz", "qux"];
+    ///
+    /// assert_eq!(v.swap_remove(1), "bar");
+    /// assert_eq!(v, ["foo", "qux", "baz"]);
+    ///
+    /// assert_eq!(v.swap_remove(0), "foo");
+    /// assert_eq!(v, ["baz", "qux"]);
+    /// ```
+    #[inline]
+    pub fn swap_remove(&mut self, index: usize) -> T {
+        unsafe {
+            // We replace self[index] with the last element. Note that if the
+            // bounds check on hole succeeds there must be a last element (which
+            // can be self[index] itself).
+            let hole: *mut T = &mut self[index];
+            let last = ptr::read(self.get_unchecked(self.len - 1));
+            self.len -= 1;
+            ptr::replace(hole, last)
+        }
+    }
+
+    /// Inserts an element at position `index` within the vector, shifting all
+    /// elements after it to the right.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3];
+    /// vec.insert(1, 4);
+    /// assert_eq!(vec, [1, 4, 2, 3]);
+    /// vec.insert(4, 5);
+    /// assert_eq!(vec, [1, 4, 2, 3, 5]);
+    /// ```
+    pub fn insert(&mut self, index: usize, element: T) {
+        let len = self.len();
+        assert!(index <= len);
+
+        // space for the new element
+        if len == self.buf.cap() {
+            self.reserve(1);
+        }
+
+        unsafe {
+            // infallible
+            // The spot to put the new value
+            {
+                let p = self.as_mut_ptr().add(index);
+                // Shift everything over to make space. (Duplicating the
+                // `index`th element into two consecutive places.)
+                ptr::copy(p, p.offset(1), len - index);
+                // Write it in, overwriting the first copy of the `index`th
+                // element.
+                ptr::write(p, element);
+            }
+            self.set_len(len + 1);
+        }
+    }
+
+    /// Removes and returns the element at position `index` within the vector,
+    /// shifting all elements after it to the left.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = bumpalo::vec![in &b; 1, 2, 3];
+    /// assert_eq!(v.remove(1), 2);
+    /// assert_eq!(v, [1, 3]);
+    /// ```
+    pub fn remove(&mut self, index: usize) -> T {
+        let len = self.len();
+        assert!(index < len);
+        unsafe {
+            // infallible
+            let ret;
+            {
+                // the place we are taking from.
+                let ptr = self.as_mut_ptr().add(index);
+                // copy it out, unsafely having a copy of the value on
+                // the stack and in the vector at the same time.
+                ret = ptr::read(ptr);
+
+                // Shift everything down to fill in that spot.
+                ptr::copy(ptr.offset(1), ptr, len - index - 1);
+            }
+            self.set_len(len - 1);
+            ret
+        }
+    }
+
+    /// Retains only the elements specified by the predicate.
+    ///
+    /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
+    /// This method operates in place and preserves the order of the retained
+    /// elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3, 4];
+    /// vec.retain(|&x| x % 2 == 0);
+    /// assert_eq!(vec, [2, 4]);
+    /// ```
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(&T) -> bool,
+    {
+        self.drain_filter(|x| !f(x));
+    }
+
+    /// Creates an iterator that removes the elements in the vector
+    /// for which the predicate returns `true` and yields the removed items.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::Bump;
+    /// use bumpalo::collections::{CollectIn, Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut numbers = bumpalo::vec![in &b; 1, 2, 3, 4, 5];
+    ///
+    /// let evens: Vec<_> = numbers.drain_filter(|x| *x % 2 == 0).collect_in(&b);
+    ///
+    /// assert_eq!(numbers, &[1, 3, 5]);
+    /// assert_eq!(evens, &[2, 4]);
+    /// ```
+    pub fn drain_filter<'a, F>(&'a mut self, filter: F) -> DrainFilter<'a, 'bump, T, F>
+    where
+        F: FnMut(&mut T) -> bool,
+    {
+        let old_len = self.len();
+
+        // Guard against us getting leaked (leak amplification)
+        unsafe {
+            self.set_len(0);
+        }
+
+        DrainFilter {
+            vec: self,
+            idx: 0,
+            del: 0,
+            old_len,
+            pred: filter,
+        }
+    }
+
+    /// Removes all but the first of consecutive elements in the vector that resolve to the same
+    /// key.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 10, 20, 21, 30, 20];
+    ///
+    /// vec.dedup_by_key(|i| *i / 10);
+    ///
+    /// assert_eq!(vec, [10, 20, 30, 20]);
+    /// ```
+    #[inline]
+    pub fn dedup_by_key<F, K>(&mut self, mut key: F)
+    where
+        F: FnMut(&mut T) -> K,
+        K: PartialEq,
+    {
+        self.dedup_by(|a, b| key(a) == key(b))
+    }
+
+    /// Removes all but the first of consecutive elements in the vector satisfying a given equality
+    /// relation.
+    ///
+    /// The `same_bucket` function is passed references to two elements from the vector and
+    /// must determine if the elements compare equal. The elements are passed in opposite order
+    /// from their order in the slice, so if `same_bucket(a, b)` returns `true`, `a` is removed.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; "foo", "bar", "Bar", "baz", "bar"];
+    ///
+    /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
+    ///
+    /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
+    /// ```
+    pub fn dedup_by<F>(&mut self, same_bucket: F)
+    where
+        F: FnMut(&mut T, &mut T) -> bool,
+    {
+        let len = {
+            let (dedup, _) = partition_dedup_by(self.as_mut_slice(), same_bucket);
+            dedup.len()
+        };
+        self.truncate(len);
+    }
+
+    /// Appends an element to the back of a vector.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the number of elements in the vector overflows a `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2];
+    /// vec.push(3);
+    /// assert_eq!(vec, [1, 2, 3]);
+    /// ```
+    #[inline]
+    pub fn push(&mut self, value: T) {
+        // This will panic or abort if we would allocate > isize::MAX bytes
+        // or if the length increment would overflow for zero-sized types.
+        if self.len == self.buf.cap() {
+            self.reserve(1);
+        }
+        unsafe {
+            let end = self.buf.ptr().add(self.len);
+            ptr::write(end, value);
+            self.len += 1;
+        }
+    }
+
+    /// Removes the last element from a vector and returns it, or [`None`] if it
+    /// is empty.
+    ///
+    /// [`None`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3];
+    /// assert_eq!(vec.pop(), Some(3));
+    /// assert_eq!(vec, [1, 2]);
+    /// ```
+    #[inline]
+    pub fn pop(&mut self) -> Option<T> {
+        if self.len == 0 {
+            None
+        } else {
+            unsafe {
+                self.len -= 1;
+                Some(ptr::read(self.as_ptr().add(self.len())))
+            }
+        }
+    }
+
+    /// Moves all the elements of `other` into `Self`, leaving `other` empty.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the number of elements in the vector overflows a `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3];
+    /// let mut vec2 = bumpalo::vec![in &b; 4, 5, 6];
+    /// vec.append(&mut vec2);
+    /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
+    /// assert_eq!(vec2, []);
+    /// ```
+    #[inline]
+    pub fn append(&mut self, other: &mut Self) {
+        unsafe {
+            self.append_elements(other.as_slice() as _);
+            other.set_len(0);
+        }
+    }
+
+    /// Appends elements to `Self` from other buffer.
+    #[inline]
+    unsafe fn append_elements(&mut self, other: *const [T]) {
+        let count = (*other).len();
+        self.reserve(count);
+        let len = self.len();
+        ptr::copy_nonoverlapping(other as *const T, self.as_mut_ptr().add(len), count);
+        self.len += count;
+    }
+
+    /// Creates a draining iterator that removes the specified range in the vector
+    /// and yields the removed items.
+    ///
+    /// Note 1: The element range is removed even if the iterator is only
+    /// partially consumed or not consumed at all.
+    ///
+    /// Note 2: It is unspecified how many elements are removed from the vector
+    /// if the `Drain` value is leaked.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::Bump;
+    /// use bumpalo::collections::{CollectIn, Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = bumpalo::vec![in &b; 1, 2, 3];
+    ///
+    /// let u: Vec<_> = v.drain(1..).collect_in(&b);
+    ///
+    /// assert_eq!(v, &[1]);
+    /// assert_eq!(u, &[2, 3]);
+    ///
+    /// // A full range clears the vector
+    /// v.drain(..);
+    /// assert_eq!(v, &[]);
+    /// ```
+    pub fn drain<R>(&mut self, range: R) -> Drain<T>
+    where
+        R: RangeBounds<usize>,
+    {
+        // Memory safety
+        //
+        // When the Drain is first created, it shortens the length of
+        // the source vector to make sure no uninitialized or moved-from elements
+        // are accessible at all if the Drain's destructor never gets to run.
+        //
+        // Drain will ptr::read out the values to remove.
+        // When finished, remaining tail of the vec is copied back to cover
+        // the hole, and the vector length is restored to the new length.
+        //
+        let len = self.len();
+        let start = match range.start_bound() {
+            Included(&n) => n,
+            Excluded(&n) => n + 1,
+            Unbounded => 0,
+        };
+        let end = match range.end_bound() {
+            Included(&n) => n + 1,
+            Excluded(&n) => n,
+            Unbounded => len,
+        };
+        assert!(start <= end);
+        assert!(end <= len);
+
+        unsafe {
+            // set self.vec length's to start, to be safe in case Drain is leaked
+            self.set_len(start);
+            // Use the borrow in the IterMut to indicate borrowing behavior of the
+            // whole Drain iterator (like &mut T).
+            let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(start), end - start);
+            Drain {
+                tail_start: end,
+                tail_len: len - end,
+                iter: range_slice.iter(),
+                vec: NonNull::from(self),
+            }
+        }
+    }
+
+    /// Clears the vector, removing all values.
+    ///
+    /// Note that this method has no effect on the allocated capacity
+    /// of the vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = bumpalo::vec![in &b; 1, 2, 3];
+    ///
+    /// v.clear();
+    ///
+    /// assert!(v.is_empty());
+    /// ```
+    #[inline]
+    pub fn clear(&mut self) {
+        self.truncate(0)
+    }
+
+    /// Returns the number of elements in the vector, also referred to
+    /// as its 'length'.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let a = bumpalo::vec![in &b; 1, 2, 3];
+    /// assert_eq!(a.len(), 3);
+    /// ```
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Returns `true` if the vector contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = Vec::new_in(&b);
+    /// assert!(v.is_empty());
+    ///
+    /// v.push(1);
+    /// assert!(!v.is_empty());
+    /// ```
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Splits the collection into two at the given index.
+    ///
+    /// Returns a newly allocated vector. `self` contains elements `[0, at)`,
+    /// and the returned vector contains elements `[at, len)`.
+    ///
+    /// Note that the capacity of `self` does not change.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `at > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3];
+    /// let vec2 = vec.split_off(1);
+    /// assert_eq!(vec, [1]);
+    /// assert_eq!(vec2, [2, 3]);
+    /// ```
+    #[inline]
+    pub fn split_off(&mut self, at: usize) -> Self {
+        assert!(at <= self.len(), "`at` out of bounds");
+
+        let other_len = self.len - at;
+        let mut other = Vec::with_capacity_in(other_len, self.buf.bump());
+
+        // Unsafely `set_len` and copy items to `other`.
+        unsafe {
+            self.set_len(at);
+            other.set_len(other_len);
+
+            ptr::copy_nonoverlapping(self.as_ptr().add(at), other.as_mut_ptr(), other.len());
+        }
+        other
+    }
+}
+
+#[cfg(feature = "boxed")]
+impl<'bump, T> Vec<'bump, T> {
+    /// Converts the vector into [`Box<[T]>`][owned slice].
+    ///
+    /// Note that this will drop any excess capacity.
+    ///
+    /// [owned slice]: ../../boxed/struct.Box.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec, vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let v = vec![in &b; 1, 2, 3];
+    ///
+    /// let slice = v.into_boxed_slice();
+    /// ```
+    pub fn into_boxed_slice(mut self) -> crate::boxed::Box<'bump, [T]> {
+        use crate::boxed::Box;
+
+        // Unlike `alloc::vec::Vec` shrinking here isn't necessary as `bumpalo::boxed::Box` doesn't own memory.
+        unsafe {
+            let slice = slice::from_raw_parts_mut(self.as_mut_ptr(), self.len);
+            let output: Box<'bump, [T]> = Box::from_raw(slice);
+            mem::forget(self);
+            output
+        }
+    }
+}
+
+impl<'bump, T: 'bump + Clone> Vec<'bump, T> {
+    /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
+    ///
+    /// If `new_len` is greater than `len`, the `Vec` is extended by the
+    /// difference, with each additional slot filled with `value`.
+    /// If `new_len` is less than `len`, the `Vec` is simply truncated.
+    ///
+    /// This method requires [`Clone`] to be able clone the passed value. If
+    /// you need more flexibility (or want to rely on [`Default`] instead of
+    /// [`Clone`]), use [`resize_with`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; "hello"];
+    /// vec.resize(3, "world");
+    /// assert_eq!(vec, ["hello", "world", "world"]);
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 3, 4];
+    /// vec.resize(2, 0);
+    /// assert_eq!(vec, [1, 2]);
+    /// ```
+    ///
+    /// [`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html
+    /// [`Default`]: https://doc.rust-lang.org/std/default/trait.Default.html
+    /// [`resize_with`]: #method.resize_with
+    pub fn resize(&mut self, new_len: usize, value: T) {
+        let len = self.len();
+
+        if new_len > len {
+            self.extend_with(new_len - len, ExtendElement(value))
+        } else {
+            self.truncate(new_len);
+        }
+    }
+
+    /// Clones and appends all elements in a slice to the `Vec`.
+    ///
+    /// Iterates over the slice `other`, clones each element, and then appends
+    /// it to this `Vec`. The `other` vector is traversed in-order.
+    ///
+    /// Note that this function is same as [`extend`] except that it is
+    /// specialized to work with slices instead. If and when Rust gets
+    /// specialization this function will likely be deprecated (but still
+    /// available).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1];
+    /// vec.extend_from_slice(&[2, 3, 4]);
+    /// assert_eq!(vec, [1, 2, 3, 4]);
+    /// ```
+    ///
+    /// [`extend`]: #method.extend
+    pub fn extend_from_slice(&mut self, other: &[T]) {
+        self.extend(other.iter().cloned())
+    }
+}
+
+// This code generalises `extend_with_{element,default}`.
+trait ExtendWith<T> {
+    fn next(&mut self) -> T;
+    fn last(self) -> T;
+}
+
+struct ExtendElement<T>(T);
+impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
+    fn next(&mut self) -> T {
+        self.0.clone()
+    }
+    fn last(self) -> T {
+        self.0
+    }
+}
+
+impl<'bump, T: 'bump> Vec<'bump, T> {
+    /// Extend the vector by `n` values, using the given generator.
+    fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
+        self.reserve(n);
+
+        unsafe {
+            let mut ptr = self.as_mut_ptr().add(self.len());
+            // Use SetLenOnDrop to work around bug where compiler
+            // may not realize the store through `ptr` through self.set_len()
+            // don't alias.
+            let mut local_len = SetLenOnDrop::new(&mut self.len);
+
+            // Write all elements except the last one
+            for _ in 1..n {
+                ptr::write(ptr, value.next());
+                ptr = ptr.offset(1);
+                // Increment the length in every step in case next() panics
+                local_len.increment_len(1);
+            }
+
+            if n > 0 {
+                // We can write the last element directly without cloning needlessly
+                ptr::write(ptr, value.last());
+                local_len.increment_len(1);
+            }
+
+            // len set by scope guard
+        }
+    }
+}
+
+// Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
+//
+// The idea is: The length field in SetLenOnDrop is a local variable
+// that the optimizer will see does not alias with any stores through the Vec's data
+// pointer. This is a workaround for alias analysis issue #32155
+struct SetLenOnDrop<'a> {
+    len: &'a mut usize,
+    local_len: usize,
+}
+
+impl<'a> SetLenOnDrop<'a> {
+    #[inline]
+    fn new(len: &'a mut usize) -> Self {
+        SetLenOnDrop {
+            local_len: *len,
+            len,
+        }
+    }
+
+    #[inline]
+    fn increment_len(&mut self, increment: usize) {
+        self.local_len += increment;
+    }
+
+    #[inline]
+    fn decrement_len(&mut self, decrement: usize) {
+        self.local_len -= decrement;
+    }
+}
+
+impl<'a> Drop for SetLenOnDrop<'a> {
+    #[inline]
+    fn drop(&mut self) {
+        *self.len = self.local_len;
+    }
+}
+
+impl<'bump, T: 'bump + PartialEq> Vec<'bump, T> {
+    /// Removes consecutive repeated elements in the vector according to the
+    /// [`PartialEq`] trait implementation.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut vec = bumpalo::vec![in &b; 1, 2, 2, 3, 2];
+    ///
+    /// vec.dedup();
+    ///
+    /// assert_eq!(vec, [1, 2, 3, 2]);
+    /// ```
+    #[inline]
+    pub fn dedup(&mut self) {
+        self.dedup_by(|a, b| a == b)
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Common trait implementations for Vec
+////////////////////////////////////////////////////////////////////////////////
+
+impl<'bump, T: 'bump + Clone> Clone for Vec<'bump, T> {
+    #[cfg(not(test))]
+    fn clone(&self) -> Vec<'bump, T> {
+        let mut v = Vec::with_capacity_in(self.len(), self.buf.bump());
+        v.extend(self.iter().cloned());
+        v
+    }
+
+    // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
+    // required for this method definition, is not available. Instead use the
+    // `slice::to_vec`  function which is only available with cfg(test)
+    // NB see the slice::hack module in slice.rs for more information
+    #[cfg(test)]
+    fn clone(&self) -> Vec<'bump, T> {
+        let mut v = Vec::new_in(self.buf.bump());
+        v.extend(self.iter().cloned());
+        v
+    }
+}
+
+impl<'bump, T: 'bump + Hash> Hash for Vec<'bump, T> {
+    #[inline]
+    fn hash<H: hash::Hasher>(&self, state: &mut H) {
+        Hash::hash(&**self, state)
+    }
+}
+
+impl<'bump, T, I> Index<I> for Vec<'bump, T>
+where
+    I: ::core::slice::SliceIndex<[T]>,
+{
+    type Output = I::Output;
+
+    #[inline]
+    fn index(&self, index: I) -> &Self::Output {
+        Index::index(&**self, index)
+    }
+}
+
+impl<'bump, T, I> IndexMut<I> for Vec<'bump, T>
+where
+    I: ::core::slice::SliceIndex<[T]>,
+{
+    #[inline]
+    fn index_mut(&mut self, index: I) -> &mut Self::Output {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+
+impl<'bump, T: 'bump> ops::Deref for Vec<'bump, T> {
+    type Target = [T];
+
+    fn deref(&self) -> &[T] {
+        unsafe {
+            let p = self.buf.ptr();
+            // assume(!p.is_null());
+            slice::from_raw_parts(p, self.len)
+        }
+    }
+}
+
+impl<'bump, T: 'bump> ops::DerefMut for Vec<'bump, T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        unsafe {
+            let ptr = self.buf.ptr();
+            // assume(!ptr.is_null());
+            slice::from_raw_parts_mut(ptr, self.len)
+        }
+    }
+}
+
+impl<'bump, T: 'bump> IntoIterator for Vec<'bump, T> {
+    type Item = T;
+    type IntoIter = IntoIter<'bump, T>;
+
+    /// Creates a consuming iterator, that is, one that moves each value out of
+    /// the vector (from start to end). The vector cannot be used after calling
+    /// this.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let v = bumpalo::vec![in &b; "a".to_string(), "b".to_string()];
+    /// for s in v.into_iter() {
+    ///     // s has type String, not &String
+    ///     println!("{}", s);
+    /// }
+    /// ```
+    #[inline]
+    fn into_iter(mut self) -> IntoIter<'bump, T> {
+        unsafe {
+            let begin = self.as_mut_ptr();
+            // assume(!begin.is_null());
+            let end = if mem::size_of::<T>() == 0 {
+                arith_offset(begin as *const i8, self.len() as isize) as *const T
+            } else {
+                begin.add(self.len()) as *const T
+            };
+            mem::forget(self);
+            IntoIter {
+                phantom: PhantomData,
+                ptr: begin,
+                end,
+            }
+        }
+    }
+}
+
+impl<'a, 'bump, T> IntoIterator for &'a Vec<'bump, T> {
+    type Item = &'a T;
+    type IntoIter = slice::Iter<'a, T>;
+
+    fn into_iter(self) -> slice::Iter<'a, T> {
+        self.iter()
+    }
+}
+
+impl<'a, 'bump, T> IntoIterator for &'a mut Vec<'bump, T> {
+    type Item = &'a mut T;
+    type IntoIter = slice::IterMut<'a, T>;
+
+    fn into_iter(self) -> slice::IterMut<'a, T> {
+        self.iter_mut()
+    }
+}
+
+impl<'bump, T: 'bump> Extend<T> for Vec<'bump, T> {
+    #[inline]
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        let iter = iter.into_iter();
+        self.reserve(iter.size_hint().0);
+
+        for t in iter {
+            self.push(t);
+        }
+    }
+}
+
+impl<'bump, T: 'bump> Vec<'bump, T> {
+    /// Creates a splicing iterator that replaces the specified range in the vector
+    /// with the given `replace_with` iterator and yields the removed items.
+    /// `replace_with` does not need to be the same length as `range`.
+    ///
+    /// Note 1: The element range is removed even if the iterator is not
+    /// consumed until the end.
+    ///
+    /// Note 2: It is unspecified how many elements are removed from the vector,
+    /// if the `Splice` value is leaked.
+    ///
+    /// Note 3: The input iterator `replace_with` is only consumed
+    /// when the `Splice` value is dropped.
+    ///
+    /// Note 4: This is optimal if:
+    ///
+    /// * The tail (elements in the vector after `range`) is empty,
+    /// * or `replace_with` yields fewer elements than `range`’s length
+    /// * or the lower bound of its `size_hint()` is exact.
+    ///
+    /// Otherwise, a temporary vector is allocated and the tail is moved twice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let mut v = bumpalo::vec![in &b; 1, 2, 3];
+    /// let new = [7, 8];
+    /// let u: Vec<_> = Vec::from_iter_in(v.splice(..2, new.iter().cloned()), &b);
+    /// assert_eq!(v, &[7, 8, 3]);
+    /// assert_eq!(u, &[1, 2]);
+    /// ```
+    #[inline]
+    pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<I::IntoIter>
+    where
+        R: RangeBounds<usize>,
+        I: IntoIterator<Item = T>,
+    {
+        Splice {
+            drain: self.drain(range),
+            replace_with: replace_with.into_iter(),
+        }
+    }
+}
+
+/// Extend implementation that copies elements out of references before pushing them onto the Vec.
+///
+/// This implementation is specialized for slice iterators, where it uses [`copy_from_slice`] to
+/// append the entire slice at once.
+///
+/// [`copy_from_slice`]: https://doc.rust-lang.org/std/primitive.slice.html#method.copy_from_slice
+impl<'a, 'bump, T: 'a + Copy> Extend<&'a T> for Vec<'bump, T> {
+    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().cloned())
+    }
+}
+
+macro_rules! __impl_slice_eq1 {
+    ($Lhs: ty, $Rhs: ty) => {
+        __impl_slice_eq1! { $Lhs, $Rhs, Sized }
+    };
+    ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
+        impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs
+        where
+            A: PartialEq<B>,
+        {
+            #[inline]
+            fn eq(&self, other: &$Rhs) -> bool {
+                self[..] == other[..]
+            }
+        }
+    };
+}
+
+__impl_slice_eq1! { Vec<'a, A>, Vec<'b, B> }
+__impl_slice_eq1! { Vec<'a, A>, &'b [B] }
+__impl_slice_eq1! { Vec<'a, A>, &'b mut [B] }
+// __impl_slice_eq1! { Cow<'a, [A]>, Vec<'b, B>, Clone }
+
+macro_rules! __impl_slice_eq1_array {
+    ($Lhs: ty, $Rhs: ty) => {
+        impl<'a, 'b, A, B, const N: usize> PartialEq<$Rhs> for $Lhs
+        where
+            A: PartialEq<B>,
+        {
+            #[inline]
+            fn eq(&self, other: &$Rhs) -> bool {
+                self[..] == other[..]
+            }
+        }
+    };
+}
+
+__impl_slice_eq1_array! { Vec<'a, A>, [B; N] }
+__impl_slice_eq1_array! { Vec<'a, A>, &'b [B; N] }
+__impl_slice_eq1_array! { Vec<'a, A>, &'b mut [B; N] }
+
+/// Implements comparison of vectors, lexicographically.
+impl<'bump, T: 'bump + PartialOrd> PartialOrd for Vec<'bump, T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Vec<'bump, T>) -> Option<Ordering> {
+        PartialOrd::partial_cmp(&**self, &**other)
+    }
+}
+
+impl<'bump, T: 'bump + Eq> Eq for Vec<'bump, T> {}
+
+/// Implements ordering of vectors, lexicographically.
+impl<'bump, T: 'bump + Ord> Ord for Vec<'bump, T> {
+    #[inline]
+    fn cmp(&self, other: &Vec<'bump, T>) -> Ordering {
+        Ord::cmp(&**self, &**other)
+    }
+}
+
+impl<'bump, T: 'bump + fmt::Debug> fmt::Debug for Vec<'bump, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'bump, T: 'bump> AsRef<Vec<'bump, T>> for Vec<'bump, T> {
+    fn as_ref(&self) -> &Vec<'bump, T> {
+        self
+    }
+}
+
+impl<'bump, T: 'bump> AsMut<Vec<'bump, T>> for Vec<'bump, T> {
+    fn as_mut(&mut self) -> &mut Vec<'bump, T> {
+        self
+    }
+}
+
+impl<'bump, T: 'bump> AsRef<[T]> for Vec<'bump, T> {
+    fn as_ref(&self) -> &[T] {
+        self
+    }
+}
+
+impl<'bump, T: 'bump> AsMut<[T]> for Vec<'bump, T> {
+    fn as_mut(&mut self) -> &mut [T] {
+        self
+    }
+}
+
+#[cfg(feature = "boxed")]
+impl<'bump, T: 'bump> From<Vec<'bump, T>> for crate::boxed::Box<'bump, [T]> {
+    fn from(v: Vec<'bump, T>) -> crate::boxed::Box<'bump, [T]> {
+        v.into_boxed_slice()
+    }
+}
+
+impl<'bump, T: 'bump> Borrow<[T]> for Vec<'bump, T> {
+    #[inline]
+    fn borrow(&self) -> &[T] {
+        &self[..]
+    }
+}
+
+impl<'bump, T: 'bump> BorrowMut<[T]> for Vec<'bump, T> {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut [T] {
+        &mut self[..]
+    }
+}
+
+impl<'bump, T> Drop for Vec<'bump, T> {
+    fn drop(&mut self) {
+        unsafe {
+            // use drop for [T]
+            // use a raw slice to refer to the elements of the vector as weakest necessary type;
+            // could avoid questions of validity in certain cases
+            ptr::drop_in_place(ptr::slice_from_raw_parts_mut(self.as_mut_ptr(), self.len))
+        }
+        // RawVec handles deallocation
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Clone-on-write
+////////////////////////////////////////////////////////////////////////////////
+
+// impl<'a, 'bump, T: Clone> From<Vec<'bump, T>> for Cow<'a, [T]> {
+//     fn from(v: Vec<'bump, T>) -> Cow<'a, [T]> {
+//         Cow::Owned(v)
+//     }
+// }
+
+// impl<'a, 'bump, T: Clone> From<&'a Vec<'bump, T>> for Cow<'a, [T]> {
+//     fn from(v: &'a Vec<'bump, T>) -> Cow<'a, [T]> {
+//         Cow::Borrowed(v.as_slice())
+//     }
+// }
+
+////////////////////////////////////////////////////////////////////////////////
+// Iterators
+////////////////////////////////////////////////////////////////////////////////
+
+/// An iterator that moves out of a vector.
+///
+/// This `struct` is created by the [`Vec::into_iter`] method
+/// (provided by the [`IntoIterator`] trait).
+///
+/// [`IntoIterator`]: https://doc.rust-lang.org/std/iter/trait.IntoIterator.html
+pub struct IntoIter<'bump, T> {
+    phantom: PhantomData<&'bump [T]>,
+    ptr: *const T,
+    end: *const T,
+}
+
+impl<'bump, T: fmt::Debug> fmt::Debug for IntoIter<'bump, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("IntoIter").field(&self.as_slice()).finish()
+    }
+}
+
+impl<'bump, T: 'bump> IntoIter<'bump, T> {
+    /// Returns the remaining items of this iterator as a slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let vec = bumpalo::vec![in &b; 'a', 'b', 'c'];
+    /// let mut into_iter = vec.into_iter();
+    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
+    /// let _ = into_iter.next().unwrap();
+    /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
+    /// ```
+    pub fn as_slice(&self) -> &[T] {
+        unsafe { slice::from_raw_parts(self.ptr, self.len()) }
+    }
+
+    /// Returns the remaining items of this iterator as a mutable slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bumpalo::{Bump, collections::Vec};
+    ///
+    /// let b = Bump::new();
+    ///
+    /// let vec = bumpalo::vec![in &b; 'a', 'b', 'c'];
+    /// let mut into_iter = vec.into_iter();
+    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
+    /// into_iter.as_mut_slice()[2] = 'z';
+    /// assert_eq!(into_iter.next().unwrap(), 'a');
+    /// assert_eq!(into_iter.next().unwrap(), 'b');
+    /// assert_eq!(into_iter.next().unwrap(), 'z');
+    /// ```
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        unsafe { slice::from_raw_parts_mut(self.ptr as *mut T, self.len()) }
+    }
+}
+
+unsafe impl<'bump, T: Send> Send for IntoIter<'bump, T> {}
+unsafe impl<'bump, T: Sync> Sync for IntoIter<'bump, T> {}
+
+impl<'bump, T: 'bump> Iterator for IntoIter<'bump, T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        unsafe {
+            if self.ptr as *const _ == self.end {
+                None
+            } else if mem::size_of::<T>() == 0 {
+                // purposefully don't use 'ptr.offset' because for
+                // vectors with 0-size elements this would return the
+                // same pointer.
+                self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
+
+                // Make up a value of this ZST.
+                Some(mem::zeroed())
+            } else {
+                let old = self.ptr;
+                self.ptr = self.ptr.offset(1);
+
+                Some(ptr::read(old))
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let exact = if mem::size_of::<T>() == 0 {
+            (self.end as usize).wrapping_sub(self.ptr as usize)
+        } else {
+            unsafe { offset_from(self.end, self.ptr) as usize }
+        };
+        (exact, Some(exact))
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+}
+
+impl<'bump, T: 'bump> DoubleEndedIterator for IntoIter<'bump, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<T> {
+        unsafe {
+            if self.end == self.ptr {
+                None
+            } else if mem::size_of::<T>() == 0 {
+                // See above for why 'ptr.offset' isn't used
+                self.end = arith_offset(self.end as *const i8, -1) as *mut T;
+
+                // Make up a value of this ZST.
+                Some(mem::zeroed())
+            } else {
+                self.end = self.end.offset(-1);
+
+                Some(ptr::read(self.end))
+            }
+        }
+    }
+}
+
+impl<'bump, T: 'bump> ExactSizeIterator for IntoIter<'bump, T> {}
+
+impl<'bump, T: 'bump> FusedIterator for IntoIter<'bump, T> {}
+
+impl<'bump, T> Drop for IntoIter<'bump, T> {
+    fn drop(&mut self) {
+        // drop all remaining elements
+        self.for_each(drop);
+    }
+}
+
+/// A draining iterator for `Vec<'bump, T>`.
+///
+/// This `struct` is created by the [`Vec::drain`] method.
+pub struct Drain<'a, 'bump, T: 'a + 'bump> {
+    /// Index of tail to preserve
+    tail_start: usize,
+    /// Length of tail
+    tail_len: usize,
+    /// Current remaining range to remove
+    iter: slice::Iter<'a, T>,
+    vec: NonNull<Vec<'bump, T>>,
+}
+
+impl<'a, 'bump, T: 'a + 'bump + fmt::Debug> fmt::Debug for Drain<'a, 'bump, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("Drain").field(&self.iter.as_slice()).finish()
+    }
+}
+
+unsafe impl<'a, 'bump, T: Sync> Sync for Drain<'a, 'bump, T> {}
+unsafe impl<'a, 'bump, T: Send> Send for Drain<'a, 'bump, T> {}
+
+impl<'a, 'bump, T> Iterator for Drain<'a, 'bump, T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        self.iter
+            .next()
+            .map(|elt| unsafe { ptr::read(elt as *const _) })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<'a, 'bump, T> DoubleEndedIterator for Drain<'a, 'bump, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<T> {
+        self.iter
+            .next_back()
+            .map(|elt| unsafe { ptr::read(elt as *const _) })
+    }
+}
+
+impl<'a, 'bump, T> Drop for Drain<'a, 'bump, T> {
+    fn drop(&mut self) {
+        // exhaust self first
+        self.for_each(drop);
+
+        if self.tail_len > 0 {
+            unsafe {
+                let source_vec = self.vec.as_mut();
+                // memmove back untouched tail, update to new length
+                let start = source_vec.len();
+                let tail = self.tail_start;
+                if tail != start {
+                    let src = source_vec.as_ptr().add(tail);
+                    let dst = source_vec.as_mut_ptr().add(start);
+                    ptr::copy(src, dst, self.tail_len);
+                }
+                source_vec.set_len(start + self.tail_len);
+            }
+        }
+    }
+}
+
+impl<'a, 'bump, T> ExactSizeIterator for Drain<'a, 'bump, T> {}
+
+impl<'a, 'bump, T> FusedIterator for Drain<'a, 'bump, T> {}
+
+/// A splicing iterator for `Vec`.
+///
+/// This struct is created by the [`Vec::splice`] method. See its
+/// documentation for more information.
+#[derive(Debug)]
+pub struct Splice<'a, 'bump, I: Iterator + 'a + 'bump> {
+    drain: Drain<'a, 'bump, I::Item>,
+    replace_with: I,
+}
+
+impl<'a, 'bump, I: Iterator> Iterator for Splice<'a, 'bump, I> {
+    type Item = I::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.drain.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.drain.size_hint()
+    }
+}
+
+impl<'a, 'bump, I: Iterator> DoubleEndedIterator for Splice<'a, 'bump, I> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.drain.next_back()
+    }
+}
+
+impl<'a, 'bump, I: Iterator> ExactSizeIterator for Splice<'a, 'bump, I> {}
+
+impl<'a, 'bump, I: Iterator> Drop for Splice<'a, 'bump, I> {
+    fn drop(&mut self) {
+        self.drain.by_ref().for_each(drop);
+
+        unsafe {
+            if self.drain.tail_len == 0 {
+                self.drain.vec.as_mut().extend(self.replace_with.by_ref());
+                return;
+            }
+
+            // First fill the range left by drain().
+            if !self.drain.fill(&mut self.replace_with) {
+                return;
+            }
+
+            // There may be more elements. Use the lower bound as an estimate.
+            // FIXME: Is the upper bound a better guess? Or something else?
+            let (lower_bound, _upper_bound) = self.replace_with.size_hint();
+            if lower_bound > 0 {
+                self.drain.move_tail(lower_bound);
+                if !self.drain.fill(&mut self.replace_with) {
+                    return;
+                }
+            }
+
+            // Collect any remaining elements.
+            // This is a zero-length vector which does not allocate if `lower_bound` was exact.
+            let mut collected = Vec::new_in(self.drain.vec.as_ref().buf.bump());
+            collected.extend(self.replace_with.by_ref());
+            let mut collected = collected.into_iter();
+            // Now we have an exact count.
+            if collected.len() > 0 {
+                self.drain.move_tail(collected.len());
+                let filled = self.drain.fill(&mut collected);
+                debug_assert!(filled);
+                debug_assert_eq!(collected.len(), 0);
+            }
+        }
+        // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
+    }
+}
+
+/// Private helper methods for `Splice::drop`
+impl<'a, 'bump, T> Drain<'a, 'bump, T> {
+    /// The range from `self.vec.len` to `self.tail_start` contains elements
+    /// that have been moved out.
+    /// Fill that range as much as possible with new elements from the `replace_with` iterator.
+    /// Return whether we filled the entire range. (`replace_with.next()` didn’t return `None`.)
+    unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool {
+        let vec = self.vec.as_mut();
+        let range_start = vec.len;
+        let range_end = self.tail_start;
+        let range_slice =
+            slice::from_raw_parts_mut(vec.as_mut_ptr().add(range_start), range_end - range_start);
+
+        for place in range_slice {
+            if let Some(new_item) = replace_with.next() {
+                ptr::write(place, new_item);
+                vec.len += 1;
+            } else {
+                return false;
+            }
+        }
+        true
+    }
+
+    /// Make room for inserting more elements before the tail.
+    unsafe fn move_tail(&mut self, extra_capacity: usize) {
+        let vec = self.vec.as_mut();
+        let used_capacity = self.tail_start + self.tail_len;
+        vec.buf.reserve(used_capacity, extra_capacity);
+
+        let new_tail_start = self.tail_start + extra_capacity;
+        let src = vec.as_ptr().add(self.tail_start);
+        let dst = vec.as_mut_ptr().add(new_tail_start);
+        ptr::copy(src, dst, self.tail_len);
+        self.tail_start = new_tail_start;
+    }
+}
+
+/// An iterator produced by calling [`Vec::drain_filter`].
+#[derive(Debug)]
+pub struct DrainFilter<'a, 'bump: 'a, T: 'a + 'bump, F>
+where
+    F: FnMut(&mut T) -> bool,
+{
+    vec: &'a mut Vec<'bump, T>,
+    idx: usize,
+    del: usize,
+    old_len: usize,
+    pred: F,
+}
+
+impl<'a, 'bump, T, F> Iterator for DrainFilter<'a, 'bump, T, F>
+where
+    F: FnMut(&mut T) -> bool,
+{
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        unsafe {
+            while self.idx != self.old_len {
+                let i = self.idx;
+                self.idx += 1;
+                let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
+                if (self.pred)(&mut v[i]) {
+                    self.del += 1;
+                    return Some(ptr::read(&v[i]));
+                } else if self.del > 0 {
+                    let del = self.del;
+                    let src: *const T = &v[i];
+                    let dst: *mut T = &mut v[i - del];
+                    // This is safe because self.vec has length 0
+                    // thus its elements will not have Drop::drop
+                    // called on them in the event of a panic.
+                    ptr::copy_nonoverlapping(src, dst, 1);
+                }
+            }
+            None
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, Some(self.old_len - self.idx))
+    }
+}
+
+impl<'a, 'bump, T, F> Drop for DrainFilter<'a, 'bump, T, F>
+where
+    F: FnMut(&mut T) -> bool,
+{
+    fn drop(&mut self) {
+        self.for_each(drop);
+        unsafe {
+            self.vec.set_len(self.old_len - self.del);
+        }
+    }
+}
diff --git a/third_party/rust/bumpalo/src/lib.rs b/third_party/rust/bumpalo/src/lib.rs
new file mode 100644
index 0000000000..be68365c81
--- /dev/null
+++ b/third_party/rust/bumpalo/src/lib.rs
@@ -0,0 +1,2019 @@
+#![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.
+    ///
+    /// ## 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();
+        }
+    }
+}