Merging upstream version 1.72.1+dfsg1.

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

14 files changed, 2673 insertions, 0 deletions

diff --git a/vendor/triomphe/.cargo-checksum.json b/vendor/triomphe/.cargo-checksum.json
new file mode 100644
index 000000000..712085ef9
--- /dev/null
+++ b/vendor/triomphe/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"Cargo.toml":"c202bbb3cde95a6a58173272683abee0935898336a6933ad70d7b672ecb983b5","LICENSE-APACHE":"a60eea817514531668d7e00765731449fe14d059d3249e0bc93b36de45f759f2","LICENSE-MIT":"15656cc11a8331f28c0986b8ab97220d3e76f98e60ed388b5ffad37dfac4710c","README.md":"b165c87151b13a2a0b639843da6f933249fe6814cd6698259172b6a27b3844a8","src/arc.rs":"dbbd13ac6d47ce2aa11a4b1af6bb858ce9bc077679d3709565d0e710a795d8b8","src/arc_borrow.rs":"df8b6ed97b41839b5be92bec8ff7b40085ae6d9d014f5571024e8bf2595a1170","src/arc_swap_support.rs":"54213ddea959fec13f1af4efb94271a9b85c531c06649899ddf8d6b939615d05","src/arc_union.rs":"b623adb5bf6f0911b5230658ad4e054d76569dc0e75fbccf41fa666112775766","src/header.rs":"051a5537d7f5aceafcb02397caf9f8a53e7e43741a41e934156f9c388bff2a7c","src/lib.rs":"657017eacbbcc9b8720ca9b278342bbfbdc6c6e25e1c6015e70fc87668cb8bb2","src/offset_arc.rs":"ebedbcc3dd46dfebcfb2976cc37252340548819b8c8c513aa4c4b2d4187c917c","src/thin_arc.rs":"dc9ad742fc4226c9f8f9b7e6ea8fb8a4aa7ea369d2723f6dcfa9bd46b4b34b0b","src/unique_arc.rs":"73308e959d0966cacd75aa2b2043a093fcb9d1b494aae9014d48c64fd1f81c8b"},"package":"f1ee9bd9239c339d714d657fac840c6d2a4f9c45f4f9ec7b0975113458be78db"}
\ No newline at end of file
diff --git a/vendor/triomphe/Cargo.toml b/vendor/triomphe/Cargo.toml
new file mode 100644
index 000000000..5cb758241
--- /dev/null
+++ b/vendor/triomphe/Cargo.toml
@@ -0,0 +1,55 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+name = "triomphe"
+version = "0.1.8"
+authors = ["The Servo Project Developers"]
+description = "A fork of std::sync::Arc with some extra functionality and without weak references (originally servo_arc)"
+readme = "README.md"
+keywords = [
+    "arc",
+    "ffi",
+    "sync",
+    "data-structure",
+]
+categories = [
+    "concurrency",
+    "data-structures",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/Manishearth/triomphe"
+
+[dependencies.arc-swap]
+version = "1.3.0"
+optional = true
+
+[dependencies.serde]
+version = "1.0"
+optional = true
+default-features = false
+
+[dependencies.stable_deref_trait]
+version = "1.1.1"
+optional = true
+default-features = false
+
+[dependencies.unsize]
+version = "1.1"
+optional = true
+
+[features]
+default = [
+    "serde",
+    "stable_deref_trait",
+    "std",
+]
+std = []
diff --git a/vendor/triomphe/LICENSE-APACHE b/vendor/triomphe/LICENSE-APACHE
new file mode 100644
index 000000000..16fe87b06
--- /dev/null
+++ b/vendor/triomphe/LICENSE-APACHE
@@ -0,0 +1,201 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
+   "Licensor" shall mean the copyright owner or entity authorized by
+   the copyright owner that is granting the License.
+
+   "Legal Entity" shall mean the union of the acting entity and all
+   other entities that control, are controlled by, or are under common
+   control with that entity. For the purposes of this definition,
+   "control" means (i) the power, direct or indirect, to cause the
+   direction or management of such entity, whether by contract or
+   otherwise, or (ii) ownership of fifty percent (50%) or more of the
+   outstanding shares, or (iii) beneficial ownership of such entity.
+
+   "You" (or "Your") shall mean an individual or Legal Entity
+   exercising permissions granted by this License.
+
+   "Source" form shall mean the preferred form for making modifications,
+   including but not limited to software source code, documentation
+   source, and configuration files.
+
+   "Object" form shall mean any form resulting from mechanical
+   transformation or translation of a Source form, including but
+   not limited to compiled object code, generated documentation,
+   and conversions to other media types.
+
+   "Work" shall mean the work of authorship, whether in Source or
+   Object form, made available under the License, as indicated by a
+   copyright notice that is included in or attached to the work
+   (an example is provided in the Appendix below).
+
+   "Derivative Works" shall mean any work, whether in Source or Object
+   form, that is based on (or derived from) the Work and for which the
+   editorial revisions, annotations, elaborations, or other modifications
+   represent, as a whole, an original work of authorship. For the purposes
+   of this License, Derivative Works shall not include works that remain
+   separable from, or merely link (or bind by name) to the interfaces of,
+   the Work and Derivative Works thereof.
+
+   "Contribution" shall mean any work of authorship, including
+   the original version of the Work and any modifications or additions
+   to that Work or Derivative Works thereof, that is intentionally
+   submitted to Licensor for inclusion in the Work by the copyright owner
+   or by an individual or Legal Entity authorized to submit on behalf of
+   the copyright owner. For the purposes of this definition, "submitted"
+   means any form of electronic, verbal, or written communication sent
+   to the Licensor or its representatives, including but not limited to
+   communication on electronic mailing lists, source code control systems,
+   and issue tracking systems that are managed by, or on behalf of, the
+   Licensor for the purpose of discussing and improving the Work, but
+   excluding communication that is conspicuously marked or otherwise
+   designated in writing by the copyright owner as "Not a Contribution."
+
+   "Contributor" shall mean Licensor and any individual or Legal Entity
+   on behalf of whom a Contribution has been received by Licensor and
+   subsequently incorporated within the Work.
+
+2. Grant of Copyright License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   copyright license to reproduce, prepare Derivative Works of,
+   publicly display, publicly perform, sublicense, and distribute the
+   Work and such Derivative Works in Source or Object form.
+
+3. Grant of Patent License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   (except as stated in this section) patent license to make, have made,
+   use, offer to sell, sell, import, and otherwise transfer the Work,
+   where such license applies only to those patent claims licensable
+   by such Contributor that are necessarily infringed by their
+   Contribution(s) alone or by combination of their Contribution(s)
+   with the Work to which such Contribution(s) was submitted. If You
+   institute patent litigation against any entity (including a
+   cross-claim or counterclaim in a lawsuit) alleging that the Work
+   or a Contribution incorporated within the Work constitutes direct
+   or contributory patent infringement, then any patent licenses
+   granted to You under this License for that Work shall terminate
+   as of the date such litigation is filed.
+
+4. Redistribution. You may reproduce and distribute copies of the
+   Work or Derivative Works thereof in any medium, with or without
+   modifications, and in Source or Object form, provided that You
+   meet the following conditions:
+
+   (a) You must give any other recipients of the Work or
+       Derivative Works a copy of this License; and
+
+   (b) You must cause any modified files to carry prominent notices
+       stating that You changed the files; and
+
+   (c) You must retain, in the Source form of any Derivative Works
+       that You distribute, all copyright, patent, trademark, and
+       attribution notices from the Source form of the Work,
+       excluding those notices that do not pertain to any part of
+       the Derivative Works; and
+
+   (d) If the Work includes a "NOTICE" text file as part of its
+       distribution, then any Derivative Works that You distribute must
+       include a readable copy of the attribution notices contained
+       within such NOTICE file, excluding those notices that do not
+       pertain to any part of the Derivative Works, in at least one
+       of the following places: within a NOTICE text file distributed
+       as part of the Derivative Works; within the Source form or
+       documentation, if provided along with the Derivative Works; or,
+       within a display generated by the Derivative Works, if and
+       wherever such third-party notices normally appear. The contents
+       of the NOTICE file are for informational purposes only and
+       do not modify the License. You may add Your own attribution
+       notices within Derivative Works that You distribute, alongside
+       or as an addendum to the NOTICE text from the Work, provided
+       that such additional attribution notices cannot be construed
+       as modifying the License.
+
+   You may add Your own copyright statement to Your modifications and
+   may provide additional or different license terms and conditions
+   for use, reproduction, or distribution of Your modifications, or
+   for any such Derivative Works as a whole, provided Your use,
+   reproduction, and distribution of the Work otherwise complies with
+   the conditions stated in this License.
+
+5. Submission of Contributions. Unless You explicitly state otherwise,
+   any Contribution intentionally submitted for inclusion in the Work
+   by You to the Licensor shall be under the terms and conditions of
+   this License, without any additional terms or conditions.
+   Notwithstanding the above, nothing herein shall supersede or modify
+   the terms of any separate license agreement you may have executed
+   with Licensor regarding such Contributions.
+
+6. Trademarks. This License does not grant permission to use the trade
+   names, trademarks, service marks, or product names of the Licensor,
+   except as required for reasonable and customary use in describing the
+   origin of the Work and reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty. Unless required by applicable law or
+   agreed to in writing, Licensor provides the Work (and each
+   Contributor provides its Contributions) on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied, including, without limitation, any warranties or conditions
+   of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+   PARTICULAR PURPOSE. You are solely responsible for determining the
+   appropriateness of using or redistributing the Work and assume any
+   risks associated with Your exercise of permissions under this License.
+
+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
+   result of this License or out of the use or inability to use the
+   Work (including but not limited to damages for loss of goodwill,
+   work stoppage, computer failure or malfunction, or any and all
+   other commercial damages or losses), even if such Contributor
+   has been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability. While redistributing
+   the Work or Derivative Works thereof, You may choose to offer,
+   and charge a fee for, acceptance of support, warranty, indemnity,
+   or other liability obligations and/or rights consistent with this
+   License. However, in accepting such obligations, You may act only
+   on Your own behalf and on Your sole responsibility, not on behalf
+   of any other Contributor, and only if You agree to indemnify,
+   defend, and hold each Contributor harmless for any liability
+   incurred by, or claims asserted against, such Contributor by reason
+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
+APPENDIX: How to apply the Apache License to your work.
+
+   To apply the Apache License to your work, attach the following
+   boilerplate notice, with the fields enclosed by brackets "[]"
+   replaced with your own identifying information. (Don't include
+   the brackets!)  The text should be enclosed in the appropriate
+   comment syntax for the file format. We also recommend that a
+   file or class name and description of purpose be included on the
+   same "printed page" as the copyright notice for easier
+   identification within third-party archives.
+
+Copyright [yyyy] [name of copyright owner]
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+	http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
diff --git a/vendor/triomphe/LICENSE-MIT b/vendor/triomphe/LICENSE-MIT
new file mode 100644
index 000000000..d74f9e93d
--- /dev/null
+++ b/vendor/triomphe/LICENSE-MIT
@@ -0,0 +1,27 @@
+MIT License
+
+Copyright (c) 2019 Manish Goregaokar
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/vendor/triomphe/README.md b/vendor/triomphe/README.md
new file mode 100644
index 000000000..c7615a843
--- /dev/null
+++ b/vendor/triomphe/README.md
@@ -0,0 +1,13 @@
+# Triomphe
+
+Fork of Arc. This has the following advantages over std::sync::Arc:
+
+ * `triomphe::Arc` doesn't support weak references: we save space by excluding the weak reference count, and we don't do extra read-modify-update operations to handle the possibility of weak references.
+ * `triomphe::UniqueArc` allows one to construct a temporarily-mutable `Arc` which can be converted to a regular `triomphe::Arc` later
+ * `triomphe::OffsetArc` can be used transparently from C++ code and is compatible with (and can be converted to/from) `triomphe::Arc`
+ * `triomphe::ArcBorrow` is functionally similar to `&triomphe::Arc<T>`, however in memory it's simply `&T`. This makes it more flexible for FFI; the source of the borrow need not be an `Arc` pinned on the stack (and can instead be a pointer from C++, or an `OffsetArc`). Additionally, this helps avoid pointer-chasing.
+ * `triomphe::Arc` has can be constructed for dynamically-sized types via `from_header_and_iter`
+ * `triomphe::ThinArc` provides thin-pointer `Arc`s to dynamically sized types
+ * `triomphe::ArcUnion` is union of two `triomphe:Arc`s which fits inside one word of memory
+
+This crate is a version of `servo_arc` meant for general community use.
\ No newline at end of file
diff --git a/vendor/triomphe/src/arc.rs b/vendor/triomphe/src/arc.rs
new file mode 100644
index 000000000..6fe022c46
--- /dev/null
+++ b/vendor/triomphe/src/arc.rs
@@ -0,0 +1,887 @@
+use alloc::alloc::handle_alloc_error;
+use alloc::boxed::Box;
+use core::alloc::Layout;
+use core::borrow;
+use core::cmp::Ordering;
+use core::convert::From;
+use core::ffi::c_void;
+use core::fmt;
+use core::hash::{Hash, Hasher};
+use core::marker::PhantomData;
+use core::mem::{ManuallyDrop, MaybeUninit};
+use core::ops::Deref;
+use core::ptr::{self, NonNull};
+use core::sync::atomic;
+use core::sync::atomic::Ordering::{Acquire, Relaxed, Release};
+use core::{isize, usize};
+
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+#[cfg(feature = "stable_deref_trait")]
+use stable_deref_trait::{CloneStableDeref, StableDeref};
+
+use crate::{abort, ArcBorrow, HeaderSlice, OffsetArc, UniqueArc};
+
+/// A soft limit on the amount of references that may be made to an `Arc`.
+///
+/// Going above this limit will abort your program (although not
+/// necessarily) at _exactly_ `MAX_REFCOUNT + 1` references.
+const MAX_REFCOUNT: usize = (isize::MAX) as usize;
+
+/// The object allocated by an Arc<T>
+#[repr(C)]
+pub(crate) struct ArcInner<T: ?Sized> {
+    pub(crate) count: atomic::AtomicUsize,
+    pub(crate) data: T,
+}
+
+unsafe impl<T: ?Sized + Sync + Send> Send for ArcInner<T> {}
+unsafe impl<T: ?Sized + Sync + Send> Sync for ArcInner<T> {}
+
+/// An atomically reference counted shared pointer
+///
+/// See the documentation for [`Arc`] in the standard library. Unlike the
+/// standard library `Arc`, this `Arc` does not support weak reference counting.
+///
+/// [`Arc`]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html
+#[repr(transparent)]
+pub struct Arc<T: ?Sized> {
+    pub(crate) p: ptr::NonNull<ArcInner<T>>,
+    pub(crate) phantom: PhantomData<T>,
+}
+
+unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
+unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
+
+impl<T> Arc<T> {
+    /// Construct an `Arc<T>`
+    #[inline]
+    pub fn new(data: T) -> Self {
+        let ptr = Box::into_raw(Box::new(ArcInner {
+            count: atomic::AtomicUsize::new(1),
+            data,
+        }));
+
+        unsafe {
+            Arc {
+                p: ptr::NonNull::new_unchecked(ptr),
+                phantom: PhantomData,
+            }
+        }
+    }
+
+    /// Reconstruct the Arc<T> from a raw pointer obtained from into_raw()
+    ///
+    /// Note: This raw pointer will be offset in the allocation and must be preceded
+    /// by the atomic count.
+    ///
+    /// It is recommended to use OffsetArc for this
+    #[inline]
+    pub unsafe fn from_raw(ptr: *const T) -> Self {
+        // FIXME: when `byte_sub` is stabilized, this can accept T: ?Sized.
+
+        // To find the corresponding pointer to the `ArcInner` we need
+        // to subtract the offset of the `data` field from the pointer.
+        let ptr = (ptr as *const u8).sub(offset_of!(ArcInner<T>, data));
+        Arc::from_raw_inner(ptr as *mut ArcInner<T>)
+    }
+
+    /// Temporarily converts |self| into a bonafide OffsetArc and exposes it to the
+    /// provided callback. The refcount is not modified.
+    #[inline(always)]
+    pub fn with_raw_offset_arc<F, U>(&self, f: F) -> U
+    where
+        F: FnOnce(&OffsetArc<T>) -> U,
+    {
+        // Synthesize transient Arc, which never touches the refcount of the ArcInner.
+        // Store transient in `ManuallyDrop`, to leave the refcount untouched.
+        let transient = unsafe { ManuallyDrop::new(Arc::into_raw_offset(ptr::read(self))) };
+
+        // Expose the transient Arc to the callback, which may clone it if it wants.
+        f(&transient)
+    }
+
+    /// Converts an `Arc` into a `OffsetArc`. This consumes the `Arc`, so the refcount
+    /// is not modified.
+    #[inline]
+    pub fn into_raw_offset(a: Self) -> OffsetArc<T> {
+        unsafe {
+            OffsetArc {
+                ptr: ptr::NonNull::new_unchecked(Arc::into_raw(a) as *mut T),
+                phantom: PhantomData,
+            }
+        }
+    }
+
+    /// Converts a `OffsetArc` into an `Arc`. This consumes the `OffsetArc`, so the refcount
+    /// is not modified.
+    #[inline]
+    pub fn from_raw_offset(a: OffsetArc<T>) -> Self {
+        let a = ManuallyDrop::new(a);
+        let ptr = a.ptr.as_ptr();
+        unsafe { Arc::from_raw(ptr) }
+    }
+
+    /// Returns the inner value, if the [`Arc`] has exactly one strong reference.
+    ///
+    /// Otherwise, an [`Err`] is returned with the same [`Arc`] that was
+    /// passed in.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use triomphe::Arc;
+    ///
+    /// let x = Arc::new(3);
+    /// assert_eq!(Arc::try_unwrap(x), Ok(3));
+    ///
+    /// let x = Arc::new(4);
+    /// let _y = Arc::clone(&x);
+    /// assert_eq!(*Arc::try_unwrap(x).unwrap_err(), 4);
+    /// ```
+    pub fn try_unwrap(this: Self) -> Result<T, Self> {
+        Self::try_unique(this).map(UniqueArc::into_inner)
+    }
+}
+
+impl<T: ?Sized> Arc<T> {
+    /// Convert the Arc<T> to a raw pointer, suitable for use across FFI
+    ///
+    /// Note: This returns a pointer to the data T, which is offset in the allocation.
+    ///
+    /// It is recommended to use OffsetArc for this.
+    #[inline]
+    pub fn into_raw(this: Self) -> *const T {
+        let this = ManuallyDrop::new(this);
+        this.as_ptr()
+    }
+
+    /// Returns the raw pointer.
+    ///
+    /// Same as into_raw except `self` isn't consumed.
+    #[inline]
+    pub fn as_ptr(&self) -> *const T {
+        // SAFETY: This cannot go through a reference to `data`, because this method
+        // is used to implement `into_raw`. To reconstruct the full `Arc` from this
+        // pointer, it needs to maintain its full provenance, and not be reduced to
+        // just the contained `T`.
+        unsafe { ptr::addr_of_mut!((*self.ptr()).data) }
+    }
+
+    /// Produce a pointer to the data that can be converted back
+    /// to an Arc. This is basically an `&Arc<T>`, without the extra indirection.
+    /// It has the benefits of an `&T` but also knows about the underlying refcount
+    /// and can be converted into more `Arc<T>`s if necessary.
+    #[inline]
+    pub fn borrow_arc(&self) -> ArcBorrow<'_, T> {
+        ArcBorrow(&**self)
+    }
+
+    /// Returns the address on the heap of the Arc itself -- not the T within it -- for memory
+    /// reporting.
+    pub fn heap_ptr(&self) -> *const c_void {
+        self.p.as_ptr() as *const ArcInner<T> as *const c_void
+    }
+
+    #[inline]
+    pub(super) fn into_raw_inner(this: Self) -> *mut ArcInner<T> {
+        let this = ManuallyDrop::new(this);
+        this.ptr()
+    }
+
+    /// Construct an `Arc` from an allocated `ArcInner`.
+    /// # Safety
+    /// The `ptr` must point to a valid instance, allocated by an `Arc`. The reference could will
+    /// not be modified.
+    pub(super) unsafe fn from_raw_inner(ptr: *mut ArcInner<T>) -> Self {
+        Arc {
+            p: ptr::NonNull::new_unchecked(ptr),
+            phantom: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub(super) fn inner(&self) -> &ArcInner<T> {
+        // This unsafety is ok because while this arc is alive we're guaranteed
+        // that the inner pointer is valid. Furthermore, we know that the
+        // `ArcInner` structure itself is `Sync` because the inner data is
+        // `Sync` as well, so we're ok loaning out an immutable pointer to these
+        // contents.
+        unsafe { &*self.ptr() }
+    }
+
+    // Non-inlined part of `drop`. Just invokes the destructor.
+    #[inline(never)]
+    unsafe fn drop_slow(&mut self) {
+        let _ = Box::from_raw(self.ptr());
+    }
+
+    /// Test pointer equality between the two Arcs, i.e. they must be the _same_
+    /// allocation
+    #[inline]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.ptr() == other.ptr()
+    }
+
+    pub(crate) fn ptr(&self) -> *mut ArcInner<T> {
+        self.p.as_ptr()
+    }
+
+    /// Allocates an `ArcInner<T>` with sufficient space for
+    /// a possibly-unsized inner value where the value has the layout provided.
+    ///
+    /// The function `mem_to_arcinner` is called with the data pointer
+    /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`.
+    ///
+    /// ## Safety
+    ///
+    /// `mem_to_arcinner` must return the same pointer, the only things that can change are
+    /// - its type
+    /// - its metadata
+    ///
+    /// `value_layout` must be correct for `T`.
+    #[allow(unused_unsafe)]
+    pub(super) unsafe fn allocate_for_layout(
+        value_layout: Layout,
+        mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>,
+    ) -> NonNull<ArcInner<T>> {
+        let layout = Layout::new::<ArcInner<()>>()
+            .extend(value_layout)
+            .unwrap()
+            .0
+            .pad_to_align();
+
+        // Safety: we propagate safety requirements to the caller
+        unsafe {
+            Arc::try_allocate_for_layout(value_layout, mem_to_arcinner)
+                .unwrap_or_else(|_| handle_alloc_error(layout))
+        }
+    }
+
+    /// Allocates an `ArcInner<T>` with sufficient space for
+    /// a possibly-unsized inner value where the value has the layout provided,
+    /// returning an error if allocation fails.
+    ///
+    /// The function `mem_to_arcinner` is called with the data pointer
+    /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`.
+    ///
+    /// ## Safety
+    ///
+    /// `mem_to_arcinner` must return the same pointer, the only things that can change are
+    /// - its type
+    /// - its metadata
+    ///
+    /// `value_layout` must be correct for `T`.
+    #[allow(unused_unsafe)]
+    unsafe fn try_allocate_for_layout(
+        value_layout: Layout,
+        mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>,
+    ) -> Result<NonNull<ArcInner<T>>, ()> {
+        let layout = Layout::new::<ArcInner<()>>()
+            .extend(value_layout)
+            .unwrap()
+            .0
+            .pad_to_align();
+
+        let ptr = NonNull::new(alloc::alloc::alloc(layout)).ok_or(())?;
+
+        // Initialize the ArcInner
+        let inner = mem_to_arcinner(ptr.as_ptr());
+        debug_assert_eq!(unsafe { Layout::for_value(&*inner) }, layout);
+
+        unsafe {
+            ptr::write(&mut (*inner).count, atomic::AtomicUsize::new(1));
+        }
+
+        // Safety: `ptr` is checked to be non-null,
+        //         `inner` is the same as `ptr` (per the safety requirements of this function)
+        unsafe { Ok(NonNull::new_unchecked(inner)) }
+    }
+}
+
+impl<H, T> Arc<HeaderSlice<H, [T]>> {
+    pub(super) fn allocate_for_header_and_slice(
+        len: usize,
+    ) -> NonNull<ArcInner<HeaderSlice<H, [T]>>> {
+        let layout = Layout::new::<H>()
+            .extend(Layout::array::<T>(len).unwrap())
+            .unwrap()
+            .0
+            .pad_to_align();
+
+        unsafe {
+            // Safety:
+            // - the provided closure does not change the pointer (except for meta & type)
+            // - the provided layout is valid for `HeaderSlice<H, [T]>`
+            Arc::allocate_for_layout(layout, |mem| {
+                // Synthesize the fat pointer. We do this by claiming we have a direct
+                // pointer to a [T], and then changing the type of the borrow. The key
+                // point here is that the length portion of the fat pointer applies
+                // only to the number of elements in the dynamically-sized portion of
+                // the type, so the value will be the same whether it points to a [T]
+                // or something else with a [T] as its last member.
+                let fake_slice = ptr::slice_from_raw_parts_mut(mem as *mut T, len);
+                fake_slice as *mut ArcInner<HeaderSlice<H, [T]>>
+            })
+        }
+    }
+}
+
+impl<T> Arc<MaybeUninit<T>> {
+    /// Create an Arc contains an `MaybeUninit<T>`.
+    pub fn new_uninit() -> Self {
+        Arc::new(MaybeUninit::<T>::uninit())
+    }
+
+    /// Calls `MaybeUninit::write` on the value contained.
+    ///
+    /// ## Panics
+    ///
+    /// If the `Arc` is not unique.
+    #[deprecated(
+        since = "0.1.7",
+        note = "this function previously was UB and now panics for non-unique `Arc`s. Use `UniqueArc::write` instead."
+    )]
+    #[track_caller]
+    pub fn write(&mut self, val: T) -> &mut T {
+        UniqueArc::write(must_be_unique(self), val)
+    }
+
+    /// Obtain a mutable pointer to the stored `MaybeUninit<T>`.
+    pub fn as_mut_ptr(&mut self) -> *mut MaybeUninit<T> {
+        unsafe { &mut (*self.ptr()).data }
+    }
+
+    /// # Safety
+    ///
+    /// Must initialize all fields before calling this function.
+    #[inline]
+    pub unsafe fn assume_init(self) -> Arc<T> {
+        Arc::from_raw_inner(ManuallyDrop::new(self).ptr().cast())
+    }
+}
+
+impl<T> Arc<[MaybeUninit<T>]> {
+    /// Create an Arc contains an array `[MaybeUninit<T>]` of `len`.
+    pub fn new_uninit_slice(len: usize) -> Self {
+        UniqueArc::new_uninit_slice(len).shareable()
+    }
+
+    /// Obtain a mutable slice to the stored `[MaybeUninit<T>]`.
+    #[deprecated(
+        since = "0.1.8",
+        note = "this function previously was UB and now panics for non-unique `Arc`s. Use `UniqueArc` or `get_mut` instead."
+    )]
+    #[track_caller]
+    pub fn as_mut_slice(&mut self) -> &mut [MaybeUninit<T>] {
+        must_be_unique(self)
+    }
+
+    /// # Safety
+    ///
+    /// Must initialize all fields before calling this function.
+    #[inline]
+    pub unsafe fn assume_init(self) -> Arc<[T]> {
+        Arc::from_raw_inner(ManuallyDrop::new(self).ptr() as _)
+    }
+}
+
+impl<T: ?Sized> Clone for Arc<T> {
+    #[inline]
+    fn clone(&self) -> Self {
+        // Using a relaxed ordering is alright here, as knowledge of the
+        // original reference prevents other threads from erroneously deleting
+        // the object.
+        //
+        // As explained in the [Boost documentation][1], Increasing the
+        // reference counter can always be done with memory_order_relaxed: New
+        // references to an object can only be formed from an existing
+        // reference, and passing an existing reference from one thread to
+        // another must already provide any required synchronization.
+        //
+        // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
+        let old_size = self.inner().count.fetch_add(1, Relaxed);
+
+        // However we need to guard against massive refcounts in case someone
+        // is `mem::forget`ing Arcs. If we don't do this the count can overflow
+        // and users will use-after free. We racily saturate to `isize::MAX` on
+        // the assumption that there aren't ~2 billion threads incrementing
+        // the reference count at once. This branch will never be taken in
+        // any realistic program.
+        //
+        // We abort because such a program is incredibly degenerate, and we
+        // don't care to support it.
+        if old_size > MAX_REFCOUNT {
+            abort();
+        }
+
+        unsafe {
+            Arc {
+                p: ptr::NonNull::new_unchecked(self.ptr()),
+                phantom: PhantomData,
+            }
+        }
+    }
+}
+
+impl<T: ?Sized> Deref for Arc<T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        &self.inner().data
+    }
+}
+
+impl<T: Clone> Arc<T> {
+    /// Makes a mutable reference to the `Arc`, cloning if necessary
+    ///
+    /// This is functionally equivalent to [`Arc::make_mut`][mm] from the standard library.
+    ///
+    /// If this `Arc` is uniquely owned, `make_mut()` will provide a mutable
+    /// reference to the contents. If not, `make_mut()` will create a _new_ `Arc`
+    /// with a copy of the contents, update `this` to point to it, and provide
+    /// a mutable reference to its contents.
+    ///
+    /// This is useful for implementing copy-on-write schemes where you wish to
+    /// avoid copying things if your `Arc` is not shared.
+    ///
+    /// [mm]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.make_mut
+    #[inline]
+    pub fn make_mut(this: &mut Self) -> &mut T {
+        if !this.is_unique() {
+            // Another pointer exists; clone
+            *this = Arc::new(T::clone(&this));
+        }
+
+        unsafe {
+            // This unsafety is ok because we're guaranteed that the pointer
+            // returned is the *only* pointer that will ever be returned to T. Our
+            // reference count is guaranteed to be 1 at this point, and we required
+            // the Arc itself to be `mut`, so we're returning the only possible
+            // reference to the inner data.
+            &mut (*this.ptr()).data
+        }
+    }
+
+    /// Makes a `UniqueArc` from an `Arc`, cloning if necessary.
+    ///
+    /// If this `Arc` is uniquely owned, `make_unique()` will provide a `UniqueArc`
+    /// containing `this`. If not, `make_unique()` will create a _new_ `Arc`
+    /// with a copy of the contents, update `this` to point to it, and provide
+    /// a `UniqueArc` to it.
+    ///
+    /// This is useful for implementing copy-on-write schemes where you wish to
+    /// avoid copying things if your `Arc` is not shared.
+    #[inline]
+    pub fn make_unique(this: &mut Self) -> &mut UniqueArc<T> {
+        if !this.is_unique() {
+            // Another pointer exists; clone
+            *this = Arc::new(T::clone(&this));
+        }
+
+        unsafe {
+            // Safety: this is either unique or just created (which is also unique)
+            UniqueArc::from_arc_ref(this)
+        }
+    }
+
+    /// If we have the only reference to `T` then unwrap it. Otherwise, clone `T` and return the clone.
+    ///
+    /// Assuming `arc_t` is of type `Arc<T>`, this function is functionally equivalent to `(*arc_t).clone()`, but will avoid cloning the inner value where possible.
+    pub fn unwrap_or_clone(this: Arc<T>) -> T {
+        Self::try_unwrap(this).unwrap_or_else(|this| T::clone(&this))
+    }
+}
+
+impl<T: ?Sized> Arc<T> {
+    /// Provides mutable access to the contents _if_ the `Arc` is uniquely owned.
+    #[inline]
+    pub fn get_mut(this: &mut Self) -> Option<&mut T> {
+        if this.is_unique() {
+            unsafe {
+                // See make_mut() for documentation of the threadsafety here.
+                Some(&mut (*this.ptr()).data)
+            }
+        } else {
+            None
+        }
+    }
+
+    /// Provides unique access to the arc _if_ the `Arc` is uniquely owned.
+    pub fn get_unique(this: &mut Self) -> Option<&mut UniqueArc<T>> {
+        Self::try_as_unique(this).ok()
+    }
+
+    /// Whether or not the `Arc` is uniquely owned (is the refcount 1?).
+    pub fn is_unique(&self) -> bool {
+        // See the extensive discussion in [1] for why this needs to be Acquire.
+        //
+        // [1] https://github.com/servo/servo/issues/21186
+        Self::count(self) == 1
+    }
+
+    /// Gets the number of [`Arc`] pointers to this allocation
+    pub fn count(this: &Self) -> usize {
+        this.inner().count.load(Acquire)
+    }
+
+    /// Returns a [`UniqueArc`] if the [`Arc`] has exactly one strong reference.
+    ///
+    /// Otherwise, an [`Err`] is returned with the same [`Arc`] that was
+    /// passed in.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use triomphe::{Arc, UniqueArc};
+    ///
+    /// let x = Arc::new(3);
+    /// assert_eq!(UniqueArc::into_inner(Arc::try_unique(x).unwrap()), 3);
+    ///
+    /// let x = Arc::new(4);
+    /// let _y = Arc::clone(&x);
+    /// assert_eq!(
+    ///     *Arc::try_unique(x).map(UniqueArc::into_inner).unwrap_err(),
+    ///     4,
+    /// );
+    /// ```
+    pub fn try_unique(this: Self) -> Result<UniqueArc<T>, Self> {
+        if this.is_unique() {
+            // Safety: The current arc is unique and making a `UniqueArc`
+            //         from it is sound
+            unsafe { Ok(UniqueArc::from_arc(this)) }
+        } else {
+            Err(this)
+        }
+    }
+
+    pub(crate) fn try_as_unique(this: &mut Self) -> Result<&mut UniqueArc<T>, &mut Self> {
+        if this.is_unique() {
+            // Safety: The current arc is unique and making a `UniqueArc`
+            //         from it is sound
+            unsafe { Ok(UniqueArc::from_arc_ref(this)) }
+        } else {
+            Err(this)
+        }
+    }
+}
+
+impl<T: ?Sized> Drop for Arc<T> {
+    #[inline]
+    fn drop(&mut self) {
+        // Because `fetch_sub` is already atomic, we do not need to synchronize
+        // with other threads unless we are going to delete the object.
+        if self.inner().count.fetch_sub(1, Release) != 1 {
+            return;
+        }
+
+        // FIXME(bholley): Use the updated comment when [2] is merged.
+        //
+        // This load is needed to prevent reordering of use of the data and
+        // deletion of the data.  Because it is marked `Release`, the decreasing
+        // of the reference count synchronizes with this `Acquire` load. This
+        // means that use of the data happens before decreasing the reference
+        // count, which happens before this load, which happens before the
+        // deletion of the data.
+        //
+        // As explained in the [Boost documentation][1],
+        //
+        // > It is important to enforce any possible access to the object in one
+        // > thread (through an existing reference) to *happen before* deleting
+        // > the object in a different thread. This is achieved by a "release"
+        // > operation after dropping a reference (any access to the object
+        // > through this reference must obviously happened before), and an
+        // > "acquire" operation before deleting the object.
+        //
+        // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
+        // [2]: https://github.com/rust-lang/rust/pull/41714
+        self.inner().count.load(Acquire);
+
+        unsafe {
+            self.drop_slow();
+        }
+    }
+}
+
+impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
+    fn eq(&self, other: &Arc<T>) -> bool {
+        Self::ptr_eq(self, other) || *(*self) == *(*other)
+    }
+
+    #[allow(clippy::partialeq_ne_impl)]
+    fn ne(&self, other: &Arc<T>) -> bool {
+        !Self::ptr_eq(self, other) && *(*self) != *(*other)
+    }
+}
+
+impl<T: ?Sized + PartialOrd> PartialOrd for Arc<T> {
+    fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering> {
+        (**self).partial_cmp(&**other)
+    }
+
+    fn lt(&self, other: &Arc<T>) -> bool {
+        *(*self) < *(*other)
+    }
+
+    fn le(&self, other: &Arc<T>) -> bool {
+        *(*self) <= *(*other)
+    }
+
+    fn gt(&self, other: &Arc<T>) -> bool {
+        *(*self) > *(*other)
+    }
+
+    fn ge(&self, other: &Arc<T>) -> bool {
+        *(*self) >= *(*other)
+    }
+}
+
+impl<T: ?Sized + Ord> Ord for Arc<T> {
+    fn cmp(&self, other: &Arc<T>) -> Ordering {
+        (**self).cmp(&**other)
+    }
+}
+
+impl<T: ?Sized + Eq> Eq for Arc<T> {}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for Arc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for Arc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized> fmt::Pointer for Arc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Pointer::fmt(&self.ptr(), f)
+    }
+}
+
+impl<T: Default> Default for Arc<T> {
+    #[inline]
+    fn default() -> Arc<T> {
+        Arc::new(Default::default())
+    }
+}
+
+impl<T: ?Sized + Hash> Hash for Arc<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (**self).hash(state)
+    }
+}
+
+impl<T> From<T> for Arc<T> {
+    #[inline]
+    fn from(t: T) -> Self {
+        Arc::new(t)
+    }
+}
+
+impl<T: ?Sized> borrow::Borrow<T> for Arc<T> {
+    #[inline]
+    fn borrow(&self) -> &T {
+        &**self
+    }
+}
+
+impl<T: ?Sized> AsRef<T> for Arc<T> {
+    #[inline]
+    fn as_ref(&self) -> &T {
+        &**self
+    }
+}
+
+#[cfg(feature = "stable_deref_trait")]
+unsafe impl<T: ?Sized> StableDeref for Arc<T> {}
+#[cfg(feature = "stable_deref_trait")]
+unsafe impl<T: ?Sized> CloneStableDeref for Arc<T> {}
+
+#[cfg(feature = "serde")]
+impl<'de, T: Deserialize<'de>> Deserialize<'de> for Arc<T> {
+    fn deserialize<D>(deserializer: D) -> Result<Arc<T>, D::Error>
+    where
+        D: ::serde::de::Deserializer<'de>,
+    {
+        T::deserialize(deserializer).map(Arc::new)
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<T: Serialize> Serialize for Arc<T> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: ::serde::ser::Serializer,
+    {
+        (**self).serialize(serializer)
+    }
+}
+
+// Safety:
+// This implementation must guarantee that it is sound to call replace_ptr with an unsized variant
+// of the pointer retuned in `as_sized_ptr`. The basic property of Unsize coercion is that safety
+// variants and layout is unaffected. The Arc does not rely on any other property of T. This makes
+// any unsized ArcInner valid for being shared with the sized variant.
+// This does _not_ mean that any T can be unsized into an U, but rather than if such unsizing is
+// possible then it can be propagated into the Arc<T>.
+#[cfg(feature = "unsize")]
+unsafe impl<T, U: ?Sized> unsize::CoerciblePtr<U> for Arc<T> {
+    type Pointee = T;
+    type Output = Arc<U>;
+
+    fn as_sized_ptr(&mut self) -> *mut T {
+        // Returns a pointer to the complete inner. The unsizing itself won't care about the
+        // pointer value and promises not to offset it.
+        self.p.as_ptr() as *mut T
+    }
+
+    unsafe fn replace_ptr(self, new: *mut U) -> Arc<U> {
+        // Fix the provenance by ensuring that of `self` is used.
+        let inner = ManuallyDrop::new(self);
+        let p = inner.p.as_ptr() as *mut T;
+        // Safety: This points to an ArcInner of the previous self and holds shared ownership since
+        // the old pointer never decremented the reference count. The caller upholds that `new` is
+        // an unsized version of the previous ArcInner. This assumes that unsizing to the fat
+        // pointer tag of an `ArcInner<U>` and `U` is isomorphic under a direct pointer cast since
+        // in reality we unsized *mut T to *mut U at the address of the ArcInner. This is the case
+        // for all currently envisioned unsized types where the tag of T and ArcInner<T> are simply
+        // the same.
+        Arc::from_raw_inner(p.replace_ptr(new) as *mut ArcInner<U>)
+    }
+}
+
+#[track_caller]
+fn must_be_unique<T: ?Sized>(arc: &mut Arc<T>) -> &mut UniqueArc<T> {
+    match Arc::try_as_unique(arc) {
+        Ok(unique) => unique,
+        Err(this) => panic!("`Arc` must be unique in order for this operation to be safe, there are currently {} copies", Arc::count(this)),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::arc::Arc;
+    use alloc::string::String;
+    use core::mem::MaybeUninit;
+    #[cfg(feature = "unsize")]
+    use unsize::{CoerceUnsize, Coercion};
+
+    #[test]
+    fn try_unwrap() {
+        let x = Arc::new(100usize);
+        let y = x.clone();
+
+        // The count should be two so `try_unwrap()` should fail
+        assert_eq!(Arc::count(&x), 2);
+        assert!(Arc::try_unwrap(x).is_err());
+
+        // Since `x` has now been dropped, the count should be 1
+        // and `try_unwrap()` should succeed
+        assert_eq!(Arc::count(&y), 1);
+        assert_eq!(Arc::try_unwrap(y), Ok(100));
+    }
+
+    #[test]
+    #[cfg(feature = "unsize")]
+    fn coerce_to_slice() {
+        let x = Arc::new([0u8; 4]);
+        let y: Arc<[u8]> = x.clone().unsize(Coercion::to_slice());
+        assert_eq!((*x).as_ptr(), (*y).as_ptr());
+    }
+
+    #[test]
+    #[cfg(feature = "unsize")]
+    fn coerce_to_dyn() {
+        let x: Arc<_> = Arc::new(|| 42u32);
+        let x: Arc<_> = x.unsize(Coercion::<_, dyn Fn() -> u32>::to_fn());
+        assert_eq!((*x)(), 42);
+    }
+
+    #[test]
+    #[allow(deprecated)]
+    fn maybeuninit() {
+        let mut arc: Arc<MaybeUninit<_>> = Arc::new_uninit();
+        arc.write(999);
+
+        let arc = unsafe { arc.assume_init() };
+        assert_eq!(*arc, 999);
+    }
+
+    #[test]
+    #[allow(deprecated)]
+    #[should_panic = "`Arc` must be unique in order for this operation to be safe"]
+    fn maybeuninit_ub_to_proceed() {
+        let mut uninit = Arc::new_uninit();
+        let clone = uninit.clone();
+
+        let x: &MaybeUninit<String> = &*clone;
+
+        // This write invalidates `x` reference
+        uninit.write(String::from("nonononono"));
+
+        // Read invalidated reference to trigger UB
+        let _ = &*x;
+    }
+
+    #[test]
+    #[allow(deprecated)]
+    #[should_panic = "`Arc` must be unique in order for this operation to be safe"]
+    fn maybeuninit_slice_ub_to_proceed() {
+        let mut uninit = Arc::new_uninit_slice(13);
+        let clone = uninit.clone();
+
+        let x: &[MaybeUninit<String>] = &*clone;
+
+        // This write invalidates `x` reference
+        uninit.as_mut_slice()[0].write(String::from("nonononono"));
+
+        // Read invalidated reference to trigger UB
+        let _ = &*x;
+    }
+
+    #[test]
+    fn maybeuninit_array() {
+        let mut arc: Arc<[MaybeUninit<_>]> = Arc::new_uninit_slice(5);
+        assert!(arc.is_unique());
+        #[allow(deprecated)]
+        for (uninit, index) in arc.as_mut_slice().iter_mut().zip(0..5) {
+            let ptr = uninit.as_mut_ptr();
+            unsafe { core::ptr::write(ptr, index) };
+        }
+
+        let arc = unsafe { arc.assume_init() };
+        assert!(arc.is_unique());
+        // Using clone to that the layout generated in new_uninit_slice is compatible
+        // with ArcInner.
+        let arcs = [
+            arc.clone(),
+            arc.clone(),
+            arc.clone(),
+            arc.clone(),
+            arc.clone(),
+        ];
+        assert_eq!(6, Arc::count(&arc));
+        // If the layout is not compatible, then the data might be corrupted.
+        assert_eq!(*arc, [0, 1, 2, 3, 4]);
+
+        // Drop the arcs and check the count and the content to
+        // make sure it isn't corrupted.
+        drop(arcs);
+        assert!(arc.is_unique());
+        assert_eq!(*arc, [0, 1, 2, 3, 4]);
+    }
+
+    #[test]
+    fn roundtrip() {
+        let arc: Arc<usize> = Arc::new(0usize);
+        let ptr = Arc::into_raw(arc);
+        unsafe {
+            let _arc = Arc::from_raw(ptr);
+        }
+    }
+}
diff --git a/vendor/triomphe/src/arc_borrow.rs b/vendor/triomphe/src/arc_borrow.rs
new file mode 100644
index 000000000..d53e1a5ea
--- /dev/null
+++ b/vendor/triomphe/src/arc_borrow.rs
@@ -0,0 +1,116 @@
+use core::mem;
+use core::mem::ManuallyDrop;
+use core::ops::Deref;
+use core::ptr;
+
+use super::Arc;
+
+/// A "borrowed `Arc`". This is a pointer to
+/// a T that is known to have been allocated within an
+/// `Arc`.
+///
+/// This is equivalent in guarantees to `&Arc<T>`, however it is
+/// a bit more flexible. To obtain an `&Arc<T>` you must have
+/// an `Arc<T>` instance somewhere pinned down until we're done with it.
+/// It's also a direct pointer to `T`, so using this involves less pointer-chasing
+///
+/// However, C++ code may hand us refcounted things as pointers to T directly,
+/// so we have to conjure up a temporary `Arc` on the stack each time. The
+/// same happens for when the object is managed by a `OffsetArc`.
+///
+/// `ArcBorrow` lets us deal with borrows of known-refcounted objects
+/// without needing to worry about where the `Arc<T>` is.
+#[derive(Debug, Eq, PartialEq)]
+#[repr(transparent)]
+pub struct ArcBorrow<'a, T: ?Sized + 'a>(pub(crate) &'a T);
+
+impl<'a, T> Copy for ArcBorrow<'a, T> {}
+impl<'a, T> Clone for ArcBorrow<'a, T> {
+    #[inline]
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<'a, T> ArcBorrow<'a, T> {
+    /// Clone this as an `Arc<T>`. This bumps the refcount.
+    #[inline]
+    pub fn clone_arc(&self) -> Arc<T> {
+        let arc = unsafe { Arc::from_raw(self.0) };
+        // addref it!
+        mem::forget(arc.clone());
+        arc
+    }
+
+    /// For constructing from a reference known to be Arc-backed,
+    /// e.g. if we obtain such a reference over FFI
+    /// TODO: should from_ref be relaxed to unsized types? It can't be
+    /// converted back to an Arc right now for unsized types.
+    #[inline]
+    pub unsafe fn from_ref(r: &'a T) -> Self {
+        ArcBorrow(r)
+    }
+
+    /// Compare two `ArcBorrow`s via pointer equality. Will only return
+    /// true if they come from the same allocation
+    #[inline]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        ptr::eq(this.0 as *const T, other.0 as *const T)
+    }
+
+    /// Temporarily converts |self| into a bonafide Arc and exposes it to the
+    /// provided callback. The refcount is not modified.
+    #[inline]
+    pub fn with_arc<F, U>(&self, f: F) -> U
+    where
+        F: FnOnce(&Arc<T>) -> U,
+        T: 'static,
+    {
+        // Synthesize transient Arc, which never touches the refcount.
+        let transient = unsafe { ManuallyDrop::new(Arc::from_raw(self.0)) };
+
+        // Expose the transient Arc to the callback, which may clone it if it wants
+        // and forward the result to the user
+        f(&transient)
+    }
+
+    /// Similar to deref, but uses the lifetime |a| rather than the lifetime of
+    /// self, which is incompatible with the signature of the Deref trait.
+    #[inline]
+    pub fn get(&self) -> &'a T {
+        self.0
+    }
+}
+
+impl<'a, T> Deref for ArcBorrow<'a, T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        self.0
+    }
+}
+
+// Safety:
+// This implementation must guarantee that it is sound to call replace_ptr with an unsized variant
+// of the pointer retuned in `as_sized_ptr`. We leverage unsizing the contained reference. This
+// continues to point to the data of an ArcInner. The reference count remains untouched which is
+// correct since the number of owners did not change. This implies the returned instance fulfills
+// its safety invariants.
+#[cfg(feature = "unsize")]
+unsafe impl<'lt, T: 'lt, U: ?Sized + 'lt> unsize::CoerciblePtr<U> for ArcBorrow<'lt, T> {
+    type Pointee = T;
+    type Output = ArcBorrow<'lt, U>;
+
+    fn as_sized_ptr(&mut self) -> *mut T {
+        // Returns a pointer to the inner data. We do not need to care about any particular
+        // provenance here, only the pointer value, which we need to reconstruct the new pointer.
+        self.0 as *const T as *mut T
+    }
+
+    unsafe fn replace_ptr(self, new: *mut U) -> ArcBorrow<'lt, U> {
+        let inner = ManuallyDrop::new(self);
+        // Safety: backed by the same Arc that backed `self`.
+        ArcBorrow(inner.0.replace_ptr(new))
+    }
+}
diff --git a/vendor/triomphe/src/arc_swap_support.rs b/vendor/triomphe/src/arc_swap_support.rs
new file mode 100644
index 000000000..195854ed3
--- /dev/null
+++ b/vendor/triomphe/src/arc_swap_support.rs
@@ -0,0 +1,42 @@
+use arc_swap::RefCnt;
+
+use crate::{Arc, ThinArc};
+use core::ffi::c_void;
+
+unsafe impl<H, T> RefCnt for ThinArc<H, T> {
+    type Base = c_void;
+
+    #[inline]
+    fn into_ptr(me: Self) -> *mut Self::Base {
+        ThinArc::into_raw(me) as *mut _
+    }
+
+    #[inline]
+    fn as_ptr(me: &Self) -> *mut Self::Base {
+        ThinArc::as_ptr(me) as *mut _
+    }
+
+    #[inline]
+    unsafe fn from_ptr(ptr: *const Self::Base) -> Self {
+        ThinArc::from_raw(ptr)
+    }
+}
+
+unsafe impl<T> RefCnt for Arc<T> {
+    type Base = T;
+
+    #[inline]
+    fn into_ptr(me: Self) -> *mut Self::Base {
+        Arc::into_raw(me) as *mut _
+    }
+
+    #[inline]
+    fn as_ptr(me: &Self) -> *mut Self::Base {
+        Arc::as_ptr(me) as *mut _
+    }
+
+    #[inline]
+    unsafe fn from_ptr(ptr: *const Self::Base) -> Self {
+        Arc::from_raw(ptr)
+    }
+}
diff --git a/vendor/triomphe/src/arc_union.rs b/vendor/triomphe/src/arc_union.rs
new file mode 100644
index 000000000..6d5cddc8f
--- /dev/null
+++ b/vendor/triomphe/src/arc_union.rs
@@ -0,0 +1,139 @@
+use core::fmt;
+use core::marker::PhantomData;
+use core::ptr;
+use core::usize;
+
+use super::{Arc, ArcBorrow};
+
+/// A tagged union that can represent `Arc<A>` or `Arc<B>` while only consuming a
+/// single word. The type is also `NonNull`, and thus can be stored in an Option
+/// without increasing size.
+///
+/// This is functionally equivalent to
+/// `enum ArcUnion<A, B> { First(Arc<A>), Second(Arc<B>)` but only takes up
+/// up a single word of stack space.
+///
+/// This could probably be extended to support four types if necessary.
+pub struct ArcUnion<A, B> {
+    p: ptr::NonNull<()>,
+    phantom_a: PhantomData<A>,
+    phantom_b: PhantomData<B>,
+}
+
+unsafe impl<A: Sync + Send, B: Send + Sync> Send for ArcUnion<A, B> {}
+unsafe impl<A: Sync + Send, B: Send + Sync> Sync for ArcUnion<A, B> {}
+
+impl<A: PartialEq, B: PartialEq> PartialEq for ArcUnion<A, B> {
+    fn eq(&self, other: &Self) -> bool {
+        use crate::ArcUnionBorrow::*;
+        match (self.borrow(), other.borrow()) {
+            (First(x), First(y)) => x == y,
+            (Second(x), Second(y)) => x == y,
+            (_, _) => false,
+        }
+    }
+}
+
+/// This represents a borrow of an `ArcUnion`.
+#[derive(Debug)]
+pub enum ArcUnionBorrow<'a, A: 'a, B: 'a> {
+    First(ArcBorrow<'a, A>),
+    Second(ArcBorrow<'a, B>),
+}
+
+impl<A, B> ArcUnion<A, B> {
+    unsafe fn new(ptr: *mut ()) -> Self {
+        ArcUnion {
+            p: ptr::NonNull::new_unchecked(ptr),
+            phantom_a: PhantomData,
+            phantom_b: PhantomData,
+        }
+    }
+
+    /// Returns true if the two values are pointer-equal.
+    #[inline]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.p == other.p
+    }
+
+    /// Returns an enum representing a borrow of either A or B.
+    pub fn borrow(&self) -> ArcUnionBorrow<A, B> {
+        if self.is_first() {
+            let ptr = self.p.as_ptr() as *const A;
+            let borrow = unsafe { ArcBorrow::from_ref(&*ptr) };
+            ArcUnionBorrow::First(borrow)
+        } else {
+            let ptr = ((self.p.as_ptr() as usize) & !0x1) as *const B;
+            let borrow = unsafe { ArcBorrow::from_ref(&*ptr) };
+            ArcUnionBorrow::Second(borrow)
+        }
+    }
+
+    /// Creates an `ArcUnion` from an instance of the first type.
+    #[inline]
+    pub fn from_first(other: Arc<A>) -> Self {
+        unsafe { Self::new(Arc::into_raw(other) as *mut _) }
+    }
+
+    /// Creates an `ArcUnion` from an instance of the second type.
+    #[inline]
+    pub fn from_second(other: Arc<B>) -> Self {
+        unsafe { Self::new(((Arc::into_raw(other) as usize) | 0x1) as *mut _) }
+    }
+
+    /// Returns true if this `ArcUnion` contains the first type.
+    #[inline]
+    pub fn is_first(&self) -> bool {
+        self.p.as_ptr() as usize & 0x1 == 0
+    }
+
+    /// Returns true if this `ArcUnion` contains the second type.
+    #[inline]
+    pub fn is_second(&self) -> bool {
+        !self.is_first()
+    }
+
+    /// Returns a borrow of the first type if applicable, otherwise `None`.
+    pub fn as_first(&self) -> Option<ArcBorrow<A>> {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => Some(x),
+            ArcUnionBorrow::Second(_) => None,
+        }
+    }
+
+    /// Returns a borrow of the second type if applicable, otherwise None.
+    pub fn as_second(&self) -> Option<ArcBorrow<B>> {
+        match self.borrow() {
+            ArcUnionBorrow::First(_) => None,
+            ArcUnionBorrow::Second(x) => Some(x),
+        }
+    }
+}
+
+impl<A, B> Clone for ArcUnion<A, B> {
+    fn clone(&self) -> Self {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => ArcUnion::from_first(x.clone_arc()),
+            ArcUnionBorrow::Second(x) => ArcUnion::from_second(x.clone_arc()),
+        }
+    }
+}
+
+impl<A, B> Drop for ArcUnion<A, B> {
+    fn drop(&mut self) {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => unsafe {
+                let _ = Arc::from_raw(&*x);
+            },
+            ArcUnionBorrow::Second(x) => unsafe {
+                let _ = Arc::from_raw(&*x);
+            },
+        }
+    }
+}
+
+impl<A: fmt::Debug, B: fmt::Debug> fmt::Debug for ArcUnion<A, B> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.borrow(), f)
+    }
+}
diff --git a/vendor/triomphe/src/header.rs b/vendor/triomphe/src/header.rs
new file mode 100644
index 000000000..e35ec48b0
--- /dev/null
+++ b/vendor/triomphe/src/header.rs
@@ -0,0 +1,378 @@
+use alloc::alloc::Layout;
+use alloc::boxed::Box;
+use alloc::string::String;
+use alloc::vec::Vec;
+use core::iter::{ExactSizeIterator, Iterator};
+use core::marker::PhantomData;
+use core::mem::{self, ManuallyDrop};
+use core::ptr::{self, addr_of_mut};
+use core::usize;
+
+use super::{Arc, ArcInner};
+
+/// Structure to allow Arc-managing some fixed-sized data and a variably-sized
+/// slice in a single allocation.
+#[derive(Debug, Eq, PartialEq, Hash, PartialOrd)]
+#[repr(C)]
+pub struct HeaderSlice<H, T: ?Sized> {
+    /// The fixed-sized data.
+    pub header: H,
+
+    /// The dynamically-sized data.
+    pub slice: T,
+}
+
+impl<H, T> Arc<HeaderSlice<H, [T]>> {
+    /// Creates an Arc for a HeaderSlice using the given header struct and
+    /// iterator to generate the slice. The resulting Arc will be fat.
+    pub fn from_header_and_iter<I>(header: H, mut items: I) -> Self
+    where
+        I: Iterator<Item = T> + ExactSizeIterator,
+    {
+        assert_ne!(mem::size_of::<T>(), 0, "Need to think about ZST");
+
+        let num_items = items.len();
+
+        let inner = Arc::allocate_for_header_and_slice(num_items);
+
+        unsafe {
+            // Write the data.
+            //
+            // Note that any panics here (i.e. from the iterator) are safe, since
+            // we'll just leak the uninitialized memory.
+            ptr::write(&mut ((*inner.as_ptr()).data.header), header);
+            if num_items != 0 {
+                let mut current = (*inner.as_ptr()).data.slice.as_mut_ptr();
+                for _ in 0..num_items {
+                    ptr::write(
+                        current,
+                        items
+                            .next()
+                            .expect("ExactSizeIterator over-reported length"),
+                    );
+                    current = current.offset(1);
+                }
+                assert!(
+                    items.next().is_none(),
+                    "ExactSizeIterator under-reported length"
+                );
+            }
+            assert!(
+                items.next().is_none(),
+                "ExactSizeIterator under-reported length"
+            );
+        }
+
+        // Safety: ptr is valid & the inner structure is fully initialized
+        Arc {
+            p: inner,
+            phantom: PhantomData,
+        }
+    }
+
+    /// Creates an Arc for a HeaderSlice using the given header struct and
+    /// iterator to generate the slice. The resulting Arc will be fat.
+    pub fn from_header_and_slice(header: H, items: &[T]) -> Self
+    where
+        T: Copy,
+    {
+        assert_ne!(mem::size_of::<T>(), 0, "Need to think about ZST");
+
+        let num_items = items.len();
+
+        let inner = Arc::allocate_for_header_and_slice(num_items);
+
+        unsafe {
+            // Write the data.
+            ptr::write(&mut ((*inner.as_ptr()).data.header), header);
+            let dst = (*inner.as_ptr()).data.slice.as_mut_ptr();
+            ptr::copy_nonoverlapping(items.as_ptr(), dst, num_items);
+        }
+
+        // Safety: ptr is valid & the inner structure is fully initialized
+        Arc {
+            p: inner,
+            phantom: PhantomData,
+        }
+    }
+
+    /// Creates an Arc for a HeaderSlice using the given header struct and
+    /// vec to generate the slice. The resulting Arc will be fat.
+    pub fn from_header_and_vec(header: H, mut v: Vec<T>) -> Self {
+        let len = v.len();
+
+        let inner = Arc::allocate_for_header_and_slice(len);
+
+        unsafe {
+            // Safety: inner is a valid pointer, so this can't go out of bounds
+            let dst = addr_of_mut!((*inner.as_ptr()).data.header);
+
+            // Safety: `dst` is valid for writes (just allocated)
+            ptr::write(dst, header);
+        }
+
+        unsafe {
+            let src = v.as_mut_ptr();
+
+            // Safety: inner is a valid pointer, so this can't go out of bounds
+            let dst = addr_of_mut!((*inner.as_ptr()).data.slice) as *mut T;
+
+            // Safety:
+            // - `src` is valid for reads for `len` (got from `Vec`)
+            // - `dst` is valid for writes for `len` (just allocated, with layout for appropriate slice)
+            // - `src` and `dst` don't overlap (separate allocations)
+            ptr::copy_nonoverlapping(src, dst, len);
+
+            // Deallocate vec without dropping `T`
+            //
+            // Safety: 0..0 elements are always initialized, 0 <= cap for any cap
+            v.set_len(0);
+        }
+
+        // Safety: ptr is valid & the inner structure is fully initialized
+        Arc {
+            p: inner,
+            phantom: PhantomData,
+        }
+    }
+}
+
+impl<H> Arc<HeaderSlice<H, str>> {
+    /// Creates an Arc for a HeaderSlice using the given header struct and
+    /// a str slice to generate the slice. The resulting Arc will be fat.
+    pub fn from_header_and_str(header: H, string: &str) -> Self {
+        let bytes = Arc::from_header_and_slice(header, string.as_bytes());
+
+        // Safety: `ArcInner` and `HeaderSlice` are `repr(C)`, `str` has the same layout as `[u8]`,
+        //         thus it's ok to "transmute" between `Arc<HeaderSlice<H, [u8]>>` and `Arc<HeaderSlice<H, str>>`.
+        //
+        //         `bytes` are a valid string since we've just got them from a valid `str`.
+        unsafe { Arc::from_raw_inner(Arc::into_raw_inner(bytes) as _) }
+    }
+}
+
+/// Header data with an inline length. Consumers that use HeaderWithLength as the
+/// Header type in HeaderSlice can take advantage of ThinArc.
+#[derive(Debug, Eq, PartialEq, Hash, PartialOrd)]
+#[repr(C)]
+pub struct HeaderWithLength<H> {
+    /// The fixed-sized data.
+    pub header: H,
+
+    /// The slice length.
+    pub length: usize,
+}
+
+impl<H> HeaderWithLength<H> {
+    /// Creates a new HeaderWithLength.
+    #[inline]
+    pub fn new(header: H, length: usize) -> Self {
+        HeaderWithLength { header, length }
+    }
+}
+
+impl<T: ?Sized> From<Arc<HeaderSlice<(), T>>> for Arc<T> {
+    fn from(this: Arc<HeaderSlice<(), T>>) -> Self {
+        debug_assert_eq!(
+            Layout::for_value::<HeaderSlice<(), T>>(&this),
+            Layout::for_value::<T>(&this.slice)
+        );
+
+        // Safety: `HeaderSlice<(), T>` and `T` has the same layout
+        unsafe { Arc::from_raw_inner(Arc::into_raw_inner(this) as _) }
+    }
+}
+
+impl<T: ?Sized> From<Arc<T>> for Arc<HeaderSlice<(), T>> {
+    fn from(this: Arc<T>) -> Self {
+        // Safety: `T` and `HeaderSlice<(), T>` has the same layout
+        unsafe { Arc::from_raw_inner(Arc::into_raw_inner(this) as _) }
+    }
+}
+
+impl<T: Copy> From<&[T]> for Arc<[T]> {
+    fn from(slice: &[T]) -> Self {
+        Arc::from_header_and_slice((), slice).into()
+    }
+}
+
+impl From<&str> for Arc<str> {
+    fn from(s: &str) -> Self {
+        Arc::from_header_and_str((), s).into()
+    }
+}
+
+impl From<String> for Arc<str> {
+    fn from(s: String) -> Self {
+        Self::from(&s[..])
+    }
+}
+
+// FIXME: once `pointer::with_metadata_of` is stable or
+//        implementable on stable without assuming ptr layout
+//        this will be able to accept `T: ?Sized`.
+impl<T> From<Box<T>> for Arc<T> {
+    fn from(b: Box<T>) -> Self {
+        let layout = Layout::for_value::<T>(&b);
+
+        // Safety: the closure only changes the type of the pointer
+        let inner = unsafe { Self::allocate_for_layout(layout, |mem| mem as *mut ArcInner<T>) };
+
+        unsafe {
+            let src = Box::into_raw(b);
+
+            // Safety: inner is a valid pointer, so this can't go out of bounds
+            let dst = addr_of_mut!((*inner.as_ptr()).data);
+
+            // Safety:
+            // - `src` is valid for reads (got from `Box`)
+            // - `dst` is valid for writes (just allocated)
+            // - `src` and `dst` don't overlap (separate allocations)
+            ptr::copy_nonoverlapping(src, dst, 1);
+
+            // Deallocate box without dropping `T`
+            //
+            // Safety:
+            // - `src` has been got from `Box::into_raw`
+            // - `ManuallyDrop<T>` is guaranteed to have the same layout as `T`
+            Box::<ManuallyDrop<T>>::from_raw(src as _);
+        }
+
+        Arc {
+            p: inner,
+            phantom: PhantomData,
+        }
+    }
+}
+
+impl<T> From<Vec<T>> for Arc<[T]> {
+    fn from(v: Vec<T>) -> Self {
+        Arc::from_header_and_vec((), v).into()
+    }
+}
+
+pub(crate) type HeaderSliceWithLength<H, T> = HeaderSlice<HeaderWithLength<H>, T>;
+
+#[cfg(test)]
+mod tests {
+    use alloc::boxed::Box;
+    use alloc::string::String;
+    use alloc::vec;
+    use core::iter;
+
+    use crate::{Arc, HeaderSlice};
+
+    #[test]
+    fn from_header_and_iter_smoke() {
+        let arc = Arc::from_header_and_iter(
+            (42u32, 17u8),
+            IntoIterator::into_iter([1u16, 2, 3, 4, 5, 6, 7]),
+        );
+
+        assert_eq!(arc.header, (42, 17));
+        assert_eq!(arc.slice, [1, 2, 3, 4, 5, 6, 7]);
+    }
+
+    #[test]
+    fn from_header_and_slice_smoke() {
+        let arc = Arc::from_header_and_slice((42u32, 17u8), &[1u16, 2, 3, 4, 5, 6, 7]);
+
+        assert_eq!(arc.header, (42, 17));
+        assert_eq!(arc.slice, [1u16, 2, 3, 4, 5, 6, 7]);
+    }
+
+    #[test]
+    fn from_header_and_vec_smoke() {
+        let arc = Arc::from_header_and_vec((42u32, 17u8), vec![1u16, 2, 3, 4, 5, 6, 7]);
+
+        assert_eq!(arc.header, (42, 17));
+        assert_eq!(arc.slice, [1u16, 2, 3, 4, 5, 6, 7]);
+    }
+
+    #[test]
+    fn from_header_and_iter_empty() {
+        let arc = Arc::from_header_and_iter((42u32, 17u8), iter::empty::<u16>());
+
+        assert_eq!(arc.header, (42, 17));
+        assert_eq!(arc.slice, []);
+    }
+
+    #[test]
+    fn from_header_and_slice_empty() {
+        let arc = Arc::from_header_and_slice((42u32, 17u8), &[1u16; 0]);
+
+        assert_eq!(arc.header, (42, 17));
+        assert_eq!(arc.slice, []);
+    }
+
+    #[test]
+    fn from_header_and_vec_empty() {
+        let arc = Arc::from_header_and_vec((42u32, 17u8), vec![1u16; 0]);
+
+        assert_eq!(arc.header, (42, 17));
+        assert_eq!(arc.slice, []);
+    }
+
+    #[test]
+    fn issue_13_empty() {
+        crate::Arc::from_header_and_iter((), iter::empty::<usize>());
+    }
+
+    #[test]
+    fn issue_13_consumption() {
+        let s: &[u8] = &[0u8; 255];
+        crate::Arc::from_header_and_iter((), s.iter().copied());
+    }
+
+    #[test]
+    fn from_header_and_str_smoke() {
+        let a = Arc::from_header_and_str(
+            42,
+            "The answer to the ultimate question of life, the universe, and everything",
+        );
+        assert_eq!(a.header, 42);
+        assert_eq!(
+            &a.slice,
+            "The answer to the ultimate question of life, the universe, and everything"
+        );
+
+        let empty = Arc::from_header_and_str((), "");
+        assert_eq!(empty.header, ());
+        assert_eq!(&empty.slice, "");
+    }
+
+    #[test]
+    fn erase_and_create_from_thin_air_header() {
+        let a: Arc<HeaderSlice<(), [u32]>> = Arc::from_header_and_slice((), &[12, 17, 16]);
+        let b: Arc<[u32]> = a.into();
+
+        assert_eq!(&*b, [12, 17, 16]);
+
+        let c: Arc<HeaderSlice<(), [u32]>> = b.into();
+
+        assert_eq!(&c.slice, [12, 17, 16]);
+        assert_eq!(c.header, ());
+    }
+
+    #[test]
+    fn from_box_and_vec() {
+        let b = Box::new(String::from("xxx"));
+        let b = Arc::<String>::from(b);
+        assert_eq!(&*b, "xxx");
+
+        let v = vec![String::from("1"), String::from("2"), String::from("3")];
+        let v = Arc::<[_]>::from(v);
+        assert_eq!(
+            &*v,
+            [String::from("1"), String::from("2"), String::from("3")]
+        );
+
+        let mut v = vec![String::from("1"), String::from("2"), String::from("3")];
+        v.reserve(10);
+        let v = Arc::<[_]>::from(v);
+        assert_eq!(
+            &*v,
+            [String::from("1"), String::from("2"), String::from("3")]
+        );
+    }
+}
diff --git a/vendor/triomphe/src/lib.rs b/vendor/triomphe/src/lib.rs
new file mode 100644
index 000000000..13d568bda
--- /dev/null
+++ b/vendor/triomphe/src/lib.rs
@@ -0,0 +1,94 @@
+// 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.
+
+//! Fork of Arc. This has the following advantages over std::sync::Arc:
+//!
+//! * `triomphe::Arc` doesn't support weak references: we save space by excluding the weak reference count, and we don't do extra read-modify-update operations to handle the possibility of weak references.
+//! * `triomphe::UniqueArc` allows one to construct a temporarily-mutable `Arc` which can be converted to a regular `triomphe::Arc` later
+//! * `triomphe::OffsetArc` can be used transparently from C++ code and is compatible with (and can be converted to/from) `triomphe::Arc`
+//! * `triomphe::ArcBorrow` is functionally similar to `&triomphe::Arc<T>`, however in memory it's simply `&T`. This makes it more flexible for FFI; the source of the borrow need not be an `Arc` pinned on the stack (and can instead be a pointer from C++, or an `OffsetArc`). Additionally, this helps avoid pointer-chasing.
+//! * `triomphe::Arc` has can be constructed for dynamically-sized types via `from_header_and_iter`
+//! * `triomphe::ThinArc` provides thin-pointer `Arc`s to dynamically sized types
+//! * `triomphe::ArcUnion` is union of two `triomphe:Arc`s which fits inside one word of memory
+
+#![allow(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate core;
+
+#[cfg(feature = "arc-swap")]
+extern crate arc_swap;
+#[cfg(feature = "serde")]
+extern crate serde;
+#[cfg(feature = "stable_deref_trait")]
+extern crate stable_deref_trait;
+#[cfg(feature = "unsize")]
+extern crate unsize;
+
+/// Calculates the offset of the specified field from the start of the named struct.
+/// This macro is impossible to be const until feature(const_ptr_offset_from) is stable.
+macro_rules! offset_of {
+    ($ty: path, $field: tt) => {{
+        // ensure the type is a named struct
+        // ensure the field exists and is accessible
+        let $ty { $field: _, .. };
+
+        let uninit = <::core::mem::MaybeUninit<$ty>>::uninit(); // const since 1.36
+
+        let base_ptr: *const $ty = uninit.as_ptr(); // const since 1.59
+
+        #[allow(unused_unsafe)]
+        let field_ptr = unsafe { ::core::ptr::addr_of!((*base_ptr).$field) }; // since 1.51
+
+        // // the const version requires feature(const_ptr_offset_from)
+        // // https://github.com/rust-lang/rust/issues/92980
+        // #[allow(unused_unsafe)]
+        // unsafe { (field_ptr as *const u8).offset_from(base_ptr as *const u8) as usize }
+
+        (field_ptr as usize) - (base_ptr as usize)
+    }};
+}
+
+mod arc;
+mod arc_borrow;
+#[cfg(feature = "arc-swap")]
+mod arc_swap_support;
+mod arc_union;
+mod header;
+mod offset_arc;
+mod thin_arc;
+mod unique_arc;
+
+pub use arc::*;
+pub use arc_borrow::*;
+pub use arc_union::*;
+pub use header::*;
+pub use offset_arc::*;
+pub use thin_arc::*;
+pub use unique_arc::*;
+
+#[cfg(feature = "std")]
+use std::process::abort;
+
+// `no_std`-compatible abort by forcing a panic while already panicing.
+#[cfg(not(feature = "std"))]
+#[cold]
+fn abort() -> ! {
+    struct PanicOnDrop;
+    impl Drop for PanicOnDrop {
+        fn drop(&mut self) {
+            panic!()
+        }
+    }
+    let _double_panicer = PanicOnDrop;
+    panic!();
+}
diff --git a/vendor/triomphe/src/offset_arc.rs b/vendor/triomphe/src/offset_arc.rs
new file mode 100644
index 000000000..9345416d4
--- /dev/null
+++ b/vendor/triomphe/src/offset_arc.rs
@@ -0,0 +1,134 @@
+use core::fmt;
+use core::marker::PhantomData;
+use core::mem::ManuallyDrop;
+use core::ops::Deref;
+use core::ptr;
+
+use super::{Arc, ArcBorrow};
+
+/// An `Arc`, except it holds a pointer to the T instead of to the
+/// entire ArcInner.
+///
+/// An `OffsetArc<T>` has the same layout and ABI as a non-null
+/// `const T*` in C, and may be used in FFI function signatures.
+///
+/// ```text
+///  Arc<T>    OffsetArc<T>
+///   |          |
+///   v          v
+///  ---------------------
+/// | RefCount | T (data) | [ArcInner<T>]
+///  ---------------------
+/// ```
+///
+/// This means that this is a direct pointer to
+/// its contained data (and can be read from by both C++ and Rust),
+/// but we can also convert it to a "regular" `Arc<T>` by removing the offset.
+///
+/// This is very useful if you have an Arc-containing struct shared between Rust and C++,
+/// and wish for C++ to be able to read the data behind the `Arc` without incurring
+/// an FFI call overhead.
+#[derive(Eq)]
+#[repr(transparent)]
+pub struct OffsetArc<T> {
+    pub(crate) ptr: ptr::NonNull<T>,
+    pub(crate) phantom: PhantomData<T>,
+}
+
+unsafe impl<T: Sync + Send> Send for OffsetArc<T> {}
+unsafe impl<T: Sync + Send> Sync for OffsetArc<T> {}
+
+impl<T> Deref for OffsetArc<T> {
+    type Target = T;
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.ptr.as_ptr() }
+    }
+}
+
+impl<T> Clone for OffsetArc<T> {
+    #[inline]
+    fn clone(&self) -> Self {
+        Arc::into_raw_offset(self.clone_arc())
+    }
+}
+
+impl<T> Drop for OffsetArc<T> {
+    fn drop(&mut self) {
+        let _ = Arc::from_raw_offset(OffsetArc {
+            ptr: self.ptr,
+            phantom: PhantomData,
+        });
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for OffsetArc<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: PartialEq> PartialEq for OffsetArc<T> {
+    fn eq(&self, other: &OffsetArc<T>) -> bool {
+        *(*self) == *(*other)
+    }
+
+    #[allow(clippy::partialeq_ne_impl)]
+    fn ne(&self, other: &OffsetArc<T>) -> bool {
+        *(*self) != *(*other)
+    }
+}
+
+impl<T> OffsetArc<T> {
+    /// Temporarily converts |self| into a bonafide Arc and exposes it to the
+    /// provided callback. The refcount is not modified.
+    #[inline]
+    pub fn with_arc<F, U>(&self, f: F) -> U
+    where
+        F: FnOnce(&Arc<T>) -> U,
+    {
+        // Synthesize transient Arc, which never touches the refcount of the ArcInner.
+        let transient = unsafe { ManuallyDrop::new(Arc::from_raw(self.ptr.as_ptr())) };
+
+        // Expose the transient Arc to the callback, which may clone it if it wants
+        // and forward the result to the user
+        f(&transient)
+    }
+
+    /// If uniquely owned, provide a mutable reference
+    /// Else create a copy, and mutate that
+    ///
+    /// This is functionally the same thing as `Arc::make_mut`
+    #[inline]
+    pub fn make_mut(&mut self) -> &mut T
+    where
+        T: Clone,
+    {
+        unsafe {
+            // extract the OffsetArc as an owned variable
+            let this = ptr::read(self);
+            // treat it as a real Arc
+            let mut arc = Arc::from_raw_offset(this);
+            // obtain the mutable reference. Cast away the lifetime
+            // This may mutate `arc`
+            let ret = Arc::make_mut(&mut arc) as *mut _;
+            // Store the possibly-mutated arc back inside, after converting
+            // it to a OffsetArc again
+            ptr::write(self, Arc::into_raw_offset(arc));
+            &mut *ret
+        }
+    }
+
+    /// Clone it as an `Arc`
+    #[inline]
+    pub fn clone_arc(&self) -> Arc<T> {
+        OffsetArc::with_arc(self, |a| a.clone())
+    }
+
+    /// Produce a pointer to the data that can be converted back
+    /// to an `Arc`
+    #[inline]
+    pub fn borrow_arc(&self) -> ArcBorrow<'_, T> {
+        ArcBorrow(&**self)
+    }
+}
diff --git a/vendor/triomphe/src/thin_arc.rs b/vendor/triomphe/src/thin_arc.rs
new file mode 100644
index 000000000..e048468ad
--- /dev/null
+++ b/vendor/triomphe/src/thin_arc.rs
@@ -0,0 +1,329 @@
+use core::ffi::c_void;
+use core::fmt;
+use core::hash::{Hash, Hasher};
+use core::iter::{ExactSizeIterator, Iterator};
+use core::marker::PhantomData;
+use core::mem::ManuallyDrop;
+use core::ops::Deref;
+use core::ptr;
+use core::usize;
+
+use super::{Arc, ArcInner, HeaderSliceWithLength, HeaderWithLength};
+
+/// A "thin" `Arc` containing dynamically sized data
+///
+/// This is functionally equivalent to `Arc<(H, [T])>`
+///
+/// When you create an `Arc` containing a dynamically sized type
+/// like `HeaderSlice<H, [T]>`, the `Arc` is represented on the stack
+/// as a "fat pointer", where the length of the slice is stored
+/// alongside the `Arc`'s pointer. In some situations you may wish to
+/// have a thin pointer instead, perhaps for FFI compatibility
+/// or space efficiency.
+///
+/// Note that we use `[T; 0]` in order to have the right alignment for `T`.
+///
+/// `ThinArc` solves this by storing the length in the allocation itself,
+/// via `HeaderSliceWithLength`.
+#[repr(transparent)]
+pub struct ThinArc<H, T> {
+    ptr: ptr::NonNull<ArcInner<HeaderSliceWithLength<H, [T; 0]>>>,
+    phantom: PhantomData<(H, T)>,
+}
+
+unsafe impl<H: Sync + Send, T: Sync + Send> Send for ThinArc<H, T> {}
+unsafe impl<H: Sync + Send, T: Sync + Send> Sync for ThinArc<H, T> {}
+
+// Synthesize a fat pointer from a thin pointer.
+//
+// See the comment around the analogous operation in from_header_and_iter.
+fn thin_to_thick<H, T>(
+    thin: *mut ArcInner<HeaderSliceWithLength<H, [T; 0]>>,
+) -> *mut ArcInner<HeaderSliceWithLength<H, [T]>> {
+    let len = unsafe { (*thin).data.header.length };
+    let fake_slice = ptr::slice_from_raw_parts_mut(thin as *mut T, len);
+
+    fake_slice as *mut ArcInner<HeaderSliceWithLength<H, [T]>>
+}
+
+impl<H, T> ThinArc<H, T> {
+    /// Temporarily converts |self| into a bonafide Arc and exposes it to the
+    /// provided callback. The refcount is not modified.
+    #[inline]
+    pub fn with_arc<F, U>(&self, f: F) -> U
+    where
+        F: FnOnce(&Arc<HeaderSliceWithLength<H, [T]>>) -> U,
+    {
+        // Synthesize transient Arc, which never touches the refcount of the ArcInner.
+        let transient = unsafe {
+            ManuallyDrop::new(Arc {
+                p: ptr::NonNull::new_unchecked(thin_to_thick(self.ptr.as_ptr())),
+                phantom: PhantomData,
+            })
+        };
+
+        // Expose the transient Arc to the callback, which may clone it if it wants
+        // and forward the result to the user
+        f(&transient)
+    }
+
+    /// Creates a `ThinArc` for a HeaderSlice using the given header struct and
+    /// iterator to generate the slice.
+    pub fn from_header_and_iter<I>(header: H, items: I) -> Self
+    where
+        I: Iterator<Item = T> + ExactSizeIterator,
+    {
+        let header = HeaderWithLength::new(header, items.len());
+        Arc::into_thin(Arc::from_header_and_iter(header, items))
+    }
+
+    /// Creates a `ThinArc` for a HeaderSlice using the given header struct and
+    /// a slice to copy.
+    pub fn from_header_and_slice(header: H, items: &[T]) -> Self
+    where
+        T: Copy,
+    {
+        let header = HeaderWithLength::new(header, items.len());
+        Arc::into_thin(Arc::from_header_and_slice(header, items))
+    }
+
+    /// Returns the address on the heap of the ThinArc itself -- not the T
+    /// within it -- for memory reporting.
+    #[inline]
+    pub fn ptr(&self) -> *const c_void {
+        self.ptr.as_ptr() as *const ArcInner<T> as *const c_void
+    }
+
+    /// Returns the address on the heap of the Arc itself -- not the T within it -- for memory
+    /// reporting.
+    #[inline]
+    pub fn heap_ptr(&self) -> *const c_void {
+        self.ptr()
+    }
+
+    /// # Safety
+    ///
+    /// Constructs an ThinArc from a raw pointer.
+    ///
+    /// The raw pointer must have been previously returned by a call to
+    /// ThinArc::into_raw.
+    ///
+    /// The user of from_raw has to make sure a specific value of T is only dropped once.
+    ///
+    /// This function is unsafe because improper use may lead to memory unsafety,
+    /// even if the returned ThinArc is never accessed.
+    #[inline]
+    pub unsafe fn from_raw(ptr: *const c_void) -> Self {
+        Self {
+            ptr: ptr::NonNull::new_unchecked(ptr as *mut c_void).cast(),
+            phantom: PhantomData,
+        }
+    }
+
+    /// Consume ThinArc and returned the wrapped pointer.
+    #[inline]
+    pub fn into_raw(self) -> *const c_void {
+        let this = ManuallyDrop::new(self);
+        this.ptr.cast().as_ptr()
+    }
+
+    /// Provides a raw pointer to the data.
+    /// The counts are not affected in any way and the ThinArc is not consumed.
+    /// The pointer is valid for as long as there are strong counts in the ThinArc.
+    #[inline]
+    pub fn as_ptr(&self) -> *const c_void {
+        self.ptr()
+    }
+}
+
+impl<H, T> Deref for ThinArc<H, T> {
+    type Target = HeaderSliceWithLength<H, [T]>;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        unsafe { &(*thin_to_thick(self.ptr.as_ptr())).data }
+    }
+}
+
+impl<H, T> Clone for ThinArc<H, T> {
+    #[inline]
+    fn clone(&self) -> Self {
+        ThinArc::with_arc(self, |a| Arc::into_thin(a.clone()))
+    }
+}
+
+impl<H, T> Drop for ThinArc<H, T> {
+    #[inline]
+    fn drop(&mut self) {
+        let _ = Arc::from_thin(ThinArc {
+            ptr: self.ptr,
+            phantom: PhantomData,
+        });
+    }
+}
+
+impl<H, T> Arc<HeaderSliceWithLength<H, [T]>> {
+    /// Converts an `Arc` into a `ThinArc`. This consumes the `Arc`, so the refcount
+    /// is not modified.
+    #[inline]
+    pub fn into_thin(a: Self) -> ThinArc<H, T> {
+        let a = ManuallyDrop::new(a);
+        assert_eq!(
+            a.header.length,
+            a.slice.len(),
+            "Length needs to be correct for ThinArc to work"
+        );
+        let fat_ptr: *mut ArcInner<HeaderSliceWithLength<H, [T]>> = a.ptr();
+        let thin_ptr = fat_ptr as *mut [usize] as *mut usize;
+        ThinArc {
+            ptr: unsafe {
+                ptr::NonNull::new_unchecked(
+                    thin_ptr as *mut ArcInner<HeaderSliceWithLength<H, [T; 0]>>,
+                )
+            },
+            phantom: PhantomData,
+        }
+    }
+
+    /// Converts a `ThinArc` into an `Arc`. This consumes the `ThinArc`, so the refcount
+    /// is not modified.
+    #[inline]
+    pub fn from_thin(a: ThinArc<H, T>) -> Self {
+        let a = ManuallyDrop::new(a);
+        let ptr = thin_to_thick(a.ptr.as_ptr());
+        unsafe {
+            Arc {
+                p: ptr::NonNull::new_unchecked(ptr),
+                phantom: PhantomData,
+            }
+        }
+    }
+}
+
+impl<H: PartialEq, T: PartialEq> PartialEq for ThinArc<H, T> {
+    #[inline]
+    fn eq(&self, other: &ThinArc<H, T>) -> bool {
+        ThinArc::with_arc(self, |a| ThinArc::with_arc(other, |b| *a == *b))
+    }
+}
+
+impl<H: Eq, T: Eq> Eq for ThinArc<H, T> {}
+
+impl<H: Hash, T: Hash> Hash for ThinArc<H, T> {
+    fn hash<HSR: Hasher>(&self, state: &mut HSR) {
+        ThinArc::with_arc(self, |a| a.hash(state))
+    }
+}
+
+impl<H: fmt::Debug, T: fmt::Debug> fmt::Debug for ThinArc<H, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<H, T> fmt::Pointer for ThinArc<H, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Pointer::fmt(&self.ptr(), f)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Arc, HeaderWithLength, ThinArc};
+    use alloc::vec;
+    use core::clone::Clone;
+    use core::ops::Drop;
+    use core::sync::atomic;
+    use core::sync::atomic::Ordering::{Acquire, SeqCst};
+
+    #[derive(PartialEq)]
+    struct Canary(*mut atomic::AtomicUsize);
+
+    impl Drop for Canary {
+        fn drop(&mut self) {
+            unsafe {
+                (*self.0).fetch_add(1, SeqCst);
+            }
+        }
+    }
+
+    #[test]
+    fn empty_thin() {
+        let header = HeaderWithLength::new(100u32, 0);
+        let x = Arc::from_header_and_iter(header, core::iter::empty::<i32>());
+        let y = Arc::into_thin(x.clone());
+        assert_eq!(y.header.header, 100);
+        assert!(y.slice.is_empty());
+        assert_eq!(x.header.header, 100);
+        assert!(x.slice.is_empty());
+    }
+
+    #[test]
+    fn thin_assert_padding() {
+        #[derive(Clone, Default)]
+        #[repr(C)]
+        struct Padded {
+            i: u16,
+        }
+
+        // The header will have more alignment than `Padded`
+        let header = HeaderWithLength::new(0i32, 2);
+        let items = vec![Padded { i: 0xdead }, Padded { i: 0xbeef }];
+        let a = ThinArc::from_header_and_iter(header, items.into_iter());
+        assert_eq!(a.slice.len(), 2);
+        assert_eq!(a.slice[0].i, 0xdead);
+        assert_eq!(a.slice[1].i, 0xbeef);
+    }
+
+    #[test]
+    #[allow(clippy::redundant_clone, clippy::eq_op)]
+    fn slices_and_thin() {
+        let mut canary = atomic::AtomicUsize::new(0);
+        let c = Canary(&mut canary as *mut atomic::AtomicUsize);
+        let v = vec![5, 6];
+        let header = HeaderWithLength::new(c, v.len());
+        {
+            let x = Arc::into_thin(Arc::from_header_and_slice(header, &v));
+            let y = ThinArc::with_arc(&x, |q| q.clone());
+            let _ = y.clone();
+            let _ = x == x;
+            Arc::from_thin(x.clone());
+        }
+        assert_eq!(canary.load(Acquire), 1);
+    }
+
+    #[test]
+    #[allow(clippy::redundant_clone, clippy::eq_op)]
+    fn iter_and_thin() {
+        let mut canary = atomic::AtomicUsize::new(0);
+        let c = Canary(&mut canary as *mut atomic::AtomicUsize);
+        let v = vec![5, 6];
+        let header = HeaderWithLength::new(c, v.len());
+        {
+            let x = Arc::into_thin(Arc::from_header_and_iter(header, v.into_iter()));
+            let y = ThinArc::with_arc(&x, |q| q.clone());
+            let _ = y.clone();
+            let _ = x == x;
+            Arc::from_thin(x.clone());
+        }
+        assert_eq!(canary.load(Acquire), 1);
+    }
+
+    #[test]
+    fn into_raw_and_from_raw() {
+        let mut canary = atomic::AtomicUsize::new(0);
+        let c = Canary(&mut canary as *mut atomic::AtomicUsize);
+        let v = vec![5, 6];
+        let header = HeaderWithLength::new(c, v.len());
+        {
+            type ThinArcCanary = ThinArc<Canary, u32>;
+            let x: ThinArcCanary = Arc::into_thin(Arc::from_header_and_iter(header, v.into_iter()));
+            let ptr = x.as_ptr();
+
+            assert_eq!(x.into_raw(), ptr);
+
+            let _x = unsafe { ThinArcCanary::from_raw(ptr) };
+        }
+        assert_eq!(canary.load(Acquire), 1);
+    }
+}
diff --git a/vendor/triomphe/src/unique_arc.rs b/vendor/triomphe/src/unique_arc.rs
new file mode 100644
index 000000000..79555fc27
--- /dev/null
+++ b/vendor/triomphe/src/unique_arc.rs
@@ -0,0 +1,257 @@
+use alloc::{alloc::Layout, boxed::Box};
+use core::convert::TryFrom;
+use core::marker::PhantomData;
+use core::mem::{ManuallyDrop, MaybeUninit};
+use core::ops::{Deref, DerefMut};
+use core::ptr::{self, NonNull};
+use core::sync::atomic::AtomicUsize;
+
+use crate::HeaderSlice;
+
+use super::{Arc, ArcInner};
+
+/// An `Arc` that is known to be uniquely owned
+///
+/// When `Arc`s are constructed, they are known to be
+/// uniquely owned. In such a case it is safe to mutate
+/// the contents of the `Arc`. Normally, one would just handle
+/// this by mutating the data on the stack before allocating the
+/// `Arc`, however it's possible the data is large or unsized
+/// and you need to heap-allocate it earlier in such a way
+/// that it can be freely converted into a regular `Arc` once you're
+/// done.
+///
+/// `UniqueArc` exists for this purpose, when constructed it performs
+/// the same allocations necessary for an `Arc`, however it allows mutable access.
+/// Once the mutation is finished, you can call `.shareable()` and get a regular `Arc`
+/// out of it.
+///
+/// ```rust
+/// # use triomphe::UniqueArc;
+/// let data = [1, 2, 3, 4, 5];
+/// let mut x = UniqueArc::new(data);
+/// x[4] = 7; // mutate!
+/// let y = x.shareable(); // y is an Arc<T>
+/// ```
+#[repr(transparent)]
+pub struct UniqueArc<T: ?Sized>(Arc<T>);
+
+impl<T> UniqueArc<T> {
+    #[inline]
+    /// Construct a new UniqueArc
+    pub fn new(data: T) -> Self {
+        UniqueArc(Arc::new(data))
+    }
+
+    /// Construct an uninitialized arc
+    #[inline]
+    pub fn new_uninit() -> UniqueArc<MaybeUninit<T>> {
+        unsafe {
+            let layout = Layout::new::<ArcInner<MaybeUninit<T>>>();
+            let ptr = alloc::alloc::alloc(layout);
+            let mut p = NonNull::new(ptr)
+                .unwrap_or_else(|| alloc::alloc::handle_alloc_error(layout))
+                .cast::<ArcInner<MaybeUninit<T>>>();
+            ptr::write(&mut p.as_mut().count, AtomicUsize::new(1));
+
+            UniqueArc(Arc {
+                p,
+                phantom: PhantomData,
+            })
+        }
+    }
+
+    /// Gets the inner value of the unique arc
+    pub fn into_inner(this: Self) -> T {
+        // Wrap the Arc in a `ManuallyDrop` so that its drop routine never runs
+        let this = ManuallyDrop::new(this.0);
+        debug_assert!(
+            this.is_unique(),
+            "attempted to call `.into_inner()` on a `UniqueArc` with a non-zero ref count",
+        );
+
+        // Safety: We have exclusive access to the inner data and the
+        //         arc will not perform its drop routine since we've
+        //         wrapped it in a `ManuallyDrop`
+        unsafe { Box::from_raw(this.ptr()).data }
+    }
+}
+
+impl<T: ?Sized> UniqueArc<T> {
+    /// Convert to a shareable Arc<T> once we're done mutating it
+    #[inline]
+    pub fn shareable(self) -> Arc<T> {
+        self.0
+    }
+
+    /// Creates a new [`UniqueArc`] from the given [`Arc`].
+    ///
+    /// An unchecked alternative to `Arc::try_unique()`
+    ///
+    /// # Safety
+    ///
+    /// The given `Arc` must have a reference count of exactly one
+    ///
+    pub(crate) unsafe fn from_arc(arc: Arc<T>) -> Self {
+        debug_assert_eq!(Arc::count(&arc), 1);
+        Self(arc)
+    }
+
+    /// Creates a new `&mut `[`UniqueArc`] from the given `&mut `[`Arc`].
+    ///
+    /// An unchecked alternative to `Arc::try_as_unique()`
+    ///
+    /// # Safety
+    ///
+    /// The given `Arc` must have a reference count of exactly one
+    pub(crate) unsafe fn from_arc_ref(arc: &mut Arc<T>) -> &mut Self {
+        debug_assert_eq!(Arc::count(&arc), 1);
+
+        // Safety: caller guarantees that `arc` is unique,
+        //         `UniqueArc` is `repr(transparent)`
+        &mut *(arc as *mut Arc<T> as *mut UniqueArc<T>)
+    }
+}
+
+impl<T> UniqueArc<MaybeUninit<T>> {
+    /// Calls `MaybeUninit::write` on the contained value.
+    pub fn write(&mut self, val: T) -> &mut T {
+        unsafe {
+            // Casting *mut MaybeUninit<T> -> *mut T is always fine
+            let ptr = self.as_mut_ptr() as *mut T;
+
+            // Safety: We have exclusive access to the inner data
+            ptr.write(val);
+
+            // Safety: the pointer was just written to
+            &mut *ptr
+        }
+    }
+
+    /// Obtain a mutable pointer to the stored `MaybeUninit<T>`.
+    pub fn as_mut_ptr(&mut self) -> *mut MaybeUninit<T> {
+        unsafe { &mut (*self.0.ptr()).data }
+    }
+
+    /// Convert to an initialized Arc.
+    ///
+    /// # Safety
+    ///
+    /// This function is equivalent to `MaybeUninit::assume_init` and has the
+    /// same safety requirements. You are responsible for ensuring that the `T`
+    /// has actually been initialized before calling this method.
+    #[inline]
+    pub unsafe fn assume_init(this: Self) -> UniqueArc<T> {
+        UniqueArc(Arc {
+            p: ManuallyDrop::new(this).0.p.cast(),
+            phantom: PhantomData,
+        })
+    }
+}
+
+impl<T> UniqueArc<[MaybeUninit<T>]> {
+    /// Create an Arc contains an array `[MaybeUninit<T>]` of `len`.
+    pub fn new_uninit_slice(len: usize) -> Self {
+        let ptr: NonNull<ArcInner<HeaderSlice<(), [MaybeUninit<T>]>>> =
+            Arc::allocate_for_header_and_slice(len);
+
+        // Safety:
+        // - `ArcInner` is properly allocated and initialized.
+        //   - `()` and `[MaybeUninit<T>]` do not require special initialization
+        // - The `Arc` is just created and so -- unique.
+        unsafe {
+            let arc: Arc<HeaderSlice<(), [MaybeUninit<T>]>> = Arc::from_raw_inner(ptr.as_ptr());
+            let arc: Arc<[MaybeUninit<T>]> = arc.into();
+            UniqueArc(arc)
+        }
+    }
+
+    /// # Safety
+    ///
+    /// Must initialize all fields before calling this function.
+    #[inline]
+    pub unsafe fn assume_init_slice(Self(this): Self) -> UniqueArc<[T]> {
+        UniqueArc(this.assume_init())
+    }
+}
+
+impl<T: ?Sized> TryFrom<Arc<T>> for UniqueArc<T> {
+    type Error = Arc<T>;
+
+    fn try_from(arc: Arc<T>) -> Result<Self, Self::Error> {
+        Arc::try_unique(arc)
+    }
+}
+
+impl<T: ?Sized> Deref for UniqueArc<T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        &*self.0
+    }
+}
+
+impl<T: ?Sized> DerefMut for UniqueArc<T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut T {
+        // We know this to be uniquely owned
+        unsafe { &mut (*self.0.ptr()).data }
+    }
+}
+
+// Safety:
+// This leverages the correctness of Arc's CoerciblePtr impl. Additionally, we must ensure that
+// this can not be used to violate the safety invariants of UniqueArc, which require that we can not
+// duplicate the Arc, such that replace_ptr returns a valid instance. This holds since it consumes
+// a unique owner of the contained ArcInner.
+#[cfg(feature = "unsize")]
+unsafe impl<T, U: ?Sized> unsize::CoerciblePtr<U> for UniqueArc<T> {
+    type Pointee = T;
+    type Output = UniqueArc<U>;
+
+    fn as_sized_ptr(&mut self) -> *mut T {
+        // Dispatch to the contained field.
+        unsize::CoerciblePtr::<U>::as_sized_ptr(&mut self.0)
+    }
+
+    unsafe fn replace_ptr(self, new: *mut U) -> UniqueArc<U> {
+        // Dispatch to the contained field, work around conflict of destructuring and Drop.
+        let inner = ManuallyDrop::new(self);
+        UniqueArc(ptr::read(&inner.0).replace_ptr(new))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Arc, UniqueArc};
+    use core::{convert::TryFrom, mem::MaybeUninit};
+
+    #[test]
+    fn unique_into_inner() {
+        let unique = UniqueArc::new(10u64);
+        assert_eq!(UniqueArc::into_inner(unique), 10);
+    }
+
+    #[test]
+    fn try_from_arc() {
+        let x = Arc::new(10_000);
+        let y = x.clone();
+
+        assert!(UniqueArc::try_from(x).is_err());
+        assert_eq!(
+            UniqueArc::into_inner(UniqueArc::try_from(y).unwrap()),
+            10_000,
+        );
+    }
+
+    #[test]
+    #[allow(deprecated)]
+    fn maybeuninit_smoke() {
+        let mut arc: UniqueArc<MaybeUninit<_>> = UniqueArc::new_uninit();
+        arc.write(999);
+
+        let arc = unsafe { UniqueArc::assume_init(arc) };
+        assert_eq!(*arc, 999);
+    }
+}