Adding upstream version 110.0.1.upstream/110.0.1upstream

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

4 files changed, 3105 insertions, 0 deletions

diff --git a/third_party/rust/thin-vec/.cargo-checksum.json b/third_party/rust/thin-vec/.cargo-checksum.json
new file mode 100644
index 0000000000..96bee9c08a
--- /dev/null
+++ b/third_party/rust/thin-vec/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"Cargo.toml":"0cf14a70308af2b73919e74765238a80556ae556d76bf5a1473088bef97710a7","README.md":"9f102f13ccbabe9cdec7a206aa298d65e33dea84da9f08dd17b358ff44fe0286","src/lib.rs":"3e34a12946625316f302459c61407d00e6b03fab60c78ac5391b1c00fad493b4"},"package":"d09c1b1ea9de6818eef6f364cc27b6a56bfd52168e33038d795ec8880a67a632"}
\ No newline at end of file
diff --git a/third_party/rust/thin-vec/Cargo.toml b/third_party/rust/thin-vec/Cargo.toml
new file mode 100644
index 0000000000..ab45ae7df0
--- /dev/null
+++ b/third_party/rust/thin-vec/Cargo.toml
@@ -0,0 +1,33 @@
+# 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]
+edition = "2018"
+name = "thin-vec"
+version = "0.2.7"
+authors = ["Aria Beingessner <a.beingessner@gmail.com>"]
+description = "A vec that takes up less space on the stack"
+homepage = "https://github.com/gankra/thin-vec"
+readme = "README.md"
+license = "MIT/Apache-2.0"
+repository = "https://github.com/gankra/thin-vec"
+
+[dependencies.serde]
+version = "1.0"
+optional = true
+
+[dev-dependencies.serde_test]
+version = "1.0"
+
+[features]
+default = []
+gecko-ffi = []
+unstable = []
diff --git a/third_party/rust/thin-vec/README.md b/third_party/rust/thin-vec/README.md
new file mode 100644
index 0000000000..e8a8c90a21
--- /dev/null
+++ b/third_party/rust/thin-vec/README.md
@@ -0,0 +1,9 @@
+![Rust CI](https://github.com/Gankra/thin-vec/workflows/Rust/badge.svg?branch=master) [![crates.io](https://img.shields.io/crates/v/thin-vec.svg)](https://crates.io/crates/thin-vec) [![](https://docs.rs/thin-vec/badge.svg)](https://docs.rs/thin-vec)
+
+# thin-vec
+
+ThinVec is a Vec that stores its length and capacity inline, making it take up
+less space.
+
+Currently this crate mostly exists to facilitate Gecko (Firefox) FFI, but it
+works perfectly fine as a native rust library as well.
diff --git a/third_party/rust/thin-vec/src/lib.rs b/third_party/rust/thin-vec/src/lib.rs
new file mode 100644
index 0000000000..1cb03f2ead
--- /dev/null
+++ b/third_party/rust/thin-vec/src/lib.rs
@@ -0,0 +1,3062 @@
+//! ThinVec is exactly the same as Vec, except that it stores its `len` and `capacity` in the buffer
+//! it allocates.
+//!
+//! This makes the memory footprint of ThinVecs lower; notably in cases where space is reserved for
+//! a non-existence ThinVec<T>. So `Vec<ThinVec<T>>` and `Option<ThinVec<T>>::None` will waste less
+//! space. Being pointer-sized also means it can be passed/stored in registers.
+//!
+//! Of course, any actually constructed ThinVec will theoretically have a bigger allocation, but
+//! the fuzzy nature of allocators means that might not actually be the case.
+//!
+//! Properties of Vec that are preserved:
+//! * `ThinVec::new()` doesn't allocate (it points to a statically allocated singleton)
+//! * reallocation can be done in place
+//! * `size_of::<ThinVec<T>>()` == `size_of::<Option<ThinVec<T>>>()`
+//!
+//! Properties of Vec that aren't preserved:
+//! * `ThinVec<T>` can't ever be zero-cost roundtripped to a `Box<[T]>`, `String`, or `*mut T`
+//! * `from_raw_parts` doesn't exist
+//! * ThinVec currently doesn't bother to not-allocate for Zero Sized Types (e.g. `ThinVec<()>`),
+//!   but it could be done if someone cared enough to implement it.
+//!
+//!
+//!
+//! # Gecko FFI
+//!
+//! If you enable the gecko-ffi feature, ThinVec will verbatim bridge with the nsTArray type in
+//! Gecko (Firefox). That is, ThinVec and nsTArray have identical layouts *but not ABIs*,
+//! so nsTArrays/ThinVecs an be natively manipulated by C++ and Rust, and ownership can be
+//! transferred across the FFI boundary (**IF YOU ARE CAREFUL, SEE BELOW!!**).
+//!
+//! While this feature is handy, it is also inherently dangerous to use because Rust and C++ do not
+//! know about each other. Specifically, this can be an issue with non-POD types (types which
+//! have destructors, move constructors, or are `!Copy`).
+//!
+//! ## Do Not Pass By Value
+//!
+//! The biggest thing to keep in mind is that **FFI functions cannot pass ThinVec/nsTArray
+//! by-value**. That is, these are busted APIs:
+//!
+//! ```rust,ignore
+//! // BAD WRONG
+//! extern fn process_data(data: ThinVec<u32>) { ... }
+//! // BAD WRONG
+//! extern fn get_data() -> ThinVec<u32> { ... }
+//! ```
+//!
+//! You must instead pass by-reference:
+//!
+//! ```rust
+//! # use thin_vec::*;
+//! # use std::mem;
+//!
+//! // Read-only access, ok!
+//! extern fn process_data(data: &ThinVec<u32>) {
+//!     for val in data {
+//!         println!("{}", val);
+//!     }
+//! }
+//!
+//! // Replace with empty instance to take ownership, ok!
+//! extern fn consume_data(data: &mut ThinVec<u32>) {
+//!     let owned = mem::replace(data, ThinVec::new());
+//!     mem::drop(owned);
+//! }
+//!
+//! // Mutate input, ok!
+//! extern fn add_data(dataset: &mut ThinVec<u32>) {
+//!     dataset.push(37);
+//!     dataset.push(12);
+//! }
+//!
+//! // Return via out-param, usually ok!
+//! //
+//! // WARNING: output must be initialized! (Empty nsTArrays are free, so just do it!)
+//! extern fn get_data(output: &mut ThinVec<u32>) {
+//!     *output = thin_vec![1, 2, 3, 4, 5];
+//! }
+//! ```
+//!
+//! Ignorable Explanation For Those Who Really Want To Know Why:
+//!
+//! > The fundamental issue is that Rust and C++ can't currently communicate about destructors, and
+//! > the semantics of C++ require destructors of function arguments to be run when the function
+//! > returns. Whether the callee or caller is responsible for this is also platform-specific, so
+//! > trying to hack around it manually would be messy.
+//! >
+//! > Also a type having a destructor changes its C++ ABI, because that type must actually exist
+//! > in memory (unlike a trivial struct, which is often passed in registers). We don't currently
+//! > have a way to communicate to Rust that this is happening, so even if we worked out the
+//! > destructor issue with say, MaybeUninit, it would still be a non-starter without some RFCs
+//! > to add explicit rustc support.
+//! >
+//! > Realistically, the best answer here is to have a "heavier" bindgen that can secretly
+//! > generate FFI glue so we can pass things "by value" and have it generate by-reference code
+//! > behind our back (like the cxx crate does). This would muddy up debugging/searchfox though.
+//!
+//! ## Types Should Be Trivially Relocatable
+//!
+//! Types in Rust are always trivially relocatable (unless suitably borrowed/[pinned][]/hidden).
+//! This means all Rust types are legal to relocate with a bitwise copy, you cannot provide
+//! copy or move constructors to execute when this happens, and the old location won't have its
+//! destructor run. This will cause problems for types which have a significant location
+//! (types that intrusively point into themselves or have their location registered with a service).
+//!
+//! While relocations are generally predictable if you're very careful, **you should avoid using
+//! types with significant locations with Rust FFI**.
+//!
+//! Specifically, ThinVec will trivially relocate its contents whenever it needs to reallocate its
+//! buffer to change its capacity. This is the default reallocation strategy for nsTArray, and is
+//! suitable for the vast majority of types. Just be aware of this limitation!
+//!
+//! ## Auto Arrays Are Dangerous
+//!
+//! ThinVec has *some* support for handling auto arrays which store their buffer on the stack,
+//! but this isn't well tested.
+//!
+//! Regardless of how much support we provide, Rust won't be aware of the buffer's limited lifetime,
+//! so standard auto array safety caveats apply about returning/storing them! ThinVec won't ever
+//! produce an auto array on its own, so this is only an issue for transferring an nsTArray into
+//! Rust.
+//!
+//! ## Other Issues
+//!
+//! Standard FFI caveats also apply:
+//!
+//!  * Rust is more strict about POD types being initialized (use MaybeUninit if you must)
+//!  * `ThinVec<T>` has no idea if the C++ version of `T` has move/copy/assign/delete overloads
+//!  * `nsTArray<T>` has no idea if the Rust version of `T` has a Drop/Clone impl
+//!  * C++ can do all sorts of unsound things that Rust can't catch
+//!  * C++ and Rust don't agree on how zero-sized/empty types should be handled
+//!
+//! The gecko-ffi feature will not work if you aren't linking with code that has nsTArray
+//! defined. Specifically, we must share the symbol for nsTArray's empty singleton. You will get
+//! linking errors if that isn't defined.
+//!
+//! The gecko-ffi feature also limits ThinVec to the legacy behaviors of nsTArray. Most notably,
+//! nsTArray has a maximum capacity of i32::MAX (~2.1 billion items). Probably not an issue.
+//! Probably.
+//!
+//! [pinned]: https://doc.rust-lang.org/std/pin/index.html
+
+#![allow(clippy::comparison_chain, clippy::missing_safety_doc)]
+
+use std::alloc::*;
+use std::borrow::*;
+use std::cmp::*;
+use std::hash::*;
+use std::iter::FromIterator;
+use std::marker::PhantomData;
+use std::ops::Bound;
+use std::ops::{Deref, DerefMut, RangeBounds};
+use std::ptr::NonNull;
+use std::slice::IterMut;
+use std::{fmt, io, mem, ptr, slice};
+
+use impl_details::*;
+
+// modules: a simple way to cfg a whole bunch of impl details at once
+
+#[cfg(not(feature = "gecko-ffi"))]
+mod impl_details {
+    pub type SizeType = usize;
+    pub const MAX_CAP: usize = !0;
+
+    #[inline(always)]
+    pub fn assert_size(x: usize) -> SizeType {
+        x
+    }
+}
+
+#[cfg(feature = "gecko-ffi")]
+mod impl_details {
+    // Support for briding a gecko nsTArray verbatim into a ThinVec.
+    //
+    // ThinVec can't see copy/move/delete implementations
+    // from C++
+    //
+    // The actual layout of an nsTArray is:
+    //
+    // ```cpp
+    // struct {
+    //   uint32_t mLength;
+    //   uint32_t mCapacity: 31;
+    //   uint32_t mIsAutoArray: 1;
+    // }
+    // ```
+    //
+    // Rust doesn't natively support bit-fields, so we manually mask
+    // and shift the bit. When the "auto" bit is set, the header and buffer
+    // are actually on the stack, meaning the ThinVec pointer-to-header
+    // is essentially an "owned borrow", and therefore dangerous to handle.
+    // There are no safety guards for this situation.
+    //
+    // On little-endian platforms, the auto bit will be the high-bit of
+    // our capacity u32. On big-endian platforms, it will be the low bit.
+    // Hence we need some platform-specific CFGs for the necessary masking/shifting.
+    //
+    // ThinVec won't ever construct an auto array. They only happen when
+    // bridging from C++. This means we don't need to ever set/preserve the bit.
+    // We just need to be able to read and handle it if it happens to be there.
+    //
+    // Handling the auto bit mostly just means not freeing/reallocating the buffer.
+
+    pub type SizeType = u32;
+
+    pub const MAX_CAP: usize = i32::max_value() as usize;
+
+    // Little endian: the auto bit is the high bit, and the capacity is
+    // verbatim. So we just need to mask off the high bit. Note that
+    // this masking is unnecessary when packing, because assert_size
+    // guards against the high bit being set.
+    #[cfg(target_endian = "little")]
+    pub fn pack_capacity(cap: SizeType) -> SizeType {
+        cap as SizeType
+    }
+    #[cfg(target_endian = "little")]
+    pub fn unpack_capacity(cap: SizeType) -> usize {
+        (cap as usize) & !(1 << 31)
+    }
+    #[cfg(target_endian = "little")]
+    pub fn is_auto(cap: SizeType) -> bool {
+        (cap & (1 << 31)) != 0
+    }
+
+    // Big endian: the auto bit is the low bit, and the capacity is
+    // shifted up one bit. Masking out the auto bit is unnecessary,
+    // as rust shifts always shift in 0's for unsigned integers.
+    #[cfg(target_endian = "big")]
+    pub fn pack_capacity(cap: SizeType) -> SizeType {
+        (cap as SizeType) << 1
+    }
+    #[cfg(target_endian = "big")]
+    pub fn unpack_capacity(cap: SizeType) -> usize {
+        (cap >> 1) as usize
+    }
+    #[cfg(target_endian = "big")]
+    pub fn is_auto(cap: SizeType) -> bool {
+        (cap & 1) != 0
+    }
+
+    #[inline]
+    pub fn assert_size(x: usize) -> SizeType {
+        if x > MAX_CAP as usize {
+            panic!("nsTArray size may not exceed the capacity of a 32-bit sized int");
+        }
+        x as SizeType
+    }
+}
+
+// The header of a ThinVec.
+//
+// The _cap can be a bitfield, so use accessors to avoid trouble.
+//
+// In "real" gecko-ffi mode, the empty singleton will be aligned
+// to 8 by gecko. But in tests we have to provide the singleton
+// ourselves, and Rust makes it hard to "just" align a static.
+// To avoid messing around with a wrapper type around the
+// singleton *just* for tests, we just force all headers to be
+// aligned to 8 in this weird "zombie" gecko mode.
+//
+// This shouldn't affect runtime layout (padding), but it will
+// result in us asking the allocator to needlessly overalign
+// non-empty ThinVecs containing align < 8 types in
+// zombie-mode, but not in "real" geck-ffi mode. Minor.
+#[cfg_attr(all(feature = "gecko-ffi", any(test, miri)), repr(align(8)))]
+#[repr(C)]
+struct Header {
+    _len: SizeType,
+    _cap: SizeType,
+}
+
+impl Header {
+    fn len(&self) -> usize {
+        self._len as usize
+    }
+
+    fn set_len(&mut self, len: usize) {
+        self._len = assert_size(len);
+    }
+}
+
+#[cfg(feature = "gecko-ffi")]
+impl Header {
+    fn cap(&self) -> usize {
+        unpack_capacity(self._cap)
+    }
+
+    fn set_cap(&mut self, cap: usize) {
+        // debug check that our packing is working
+        debug_assert_eq!(unpack_capacity(pack_capacity(cap as SizeType)), cap);
+        // FIXME: this assert is busted because it reads uninit memory
+        // debug_assert!(!self.uses_stack_allocated_buffer());
+
+        // NOTE: this always stores a cleared auto bit, because set_cap
+        // is only invoked by Rust, and Rust doesn't create auto arrays.
+        self._cap = pack_capacity(assert_size(cap));
+    }
+
+    fn uses_stack_allocated_buffer(&self) -> bool {
+        is_auto(self._cap)
+    }
+}
+
+#[cfg(not(feature = "gecko-ffi"))]
+impl Header {
+    fn cap(&self) -> usize {
+        self._cap as usize
+    }
+
+    fn set_cap(&mut self, cap: usize) {
+        self._cap = assert_size(cap);
+    }
+}
+
+/// Singleton that all empty collections share.
+/// Note: can't store non-zero ZSTs, we allocate in that case. We could
+/// optimize everything to not do that (basically, make ptr == len and branch
+/// on size == 0 in every method), but it's a bunch of work for something that
+/// doesn't matter much.
+#[cfg(any(not(feature = "gecko-ffi"), test, miri))]
+static EMPTY_HEADER: Header = Header { _len: 0, _cap: 0 };
+
+#[cfg(all(feature = "gecko-ffi", not(test), not(miri)))]
+extern "C" {
+    #[link_name = "sEmptyTArrayHeader"]
+    static EMPTY_HEADER: Header;
+}
+
+// TODO: overflow checks everywhere
+
+// Utils for computing layouts of allocations
+
+fn alloc_size<T>(cap: usize) -> usize {
+    // Compute "real" header size with pointer math
+    let header_size = mem::size_of::<Header>();
+    let elem_size = mem::size_of::<T>();
+    let padding = padding::<T>();
+
+    // TODO: care about isize::MAX overflow?
+    let data_size = elem_size.checked_mul(cap).expect("capacity overflow");
+
+    data_size
+        .checked_add(header_size + padding)
+        .expect("capacity overflow")
+}
+
+fn padding<T>() -> usize {
+    let alloc_align = alloc_align::<T>();
+    let header_size = mem::size_of::<Header>();
+
+    if alloc_align > header_size {
+        if cfg!(feature = "gecko-ffi") {
+            panic!(
+                "nsTArray does not handle alignment above > {} correctly",
+                header_size
+            );
+        }
+        alloc_align - header_size
+    } else {
+        0
+    }
+}
+
+fn alloc_align<T>() -> usize {
+    max(mem::align_of::<T>(), mem::align_of::<Header>())
+}
+
+fn layout<T>(cap: usize) -> Layout {
+    unsafe { Layout::from_size_align_unchecked(alloc_size::<T>(cap), alloc_align::<T>()) }
+}
+
+fn header_with_capacity<T>(cap: usize) -> NonNull<Header> {
+    debug_assert!(cap > 0);
+    unsafe {
+        let layout = layout::<T>(cap);
+        let header = alloc(layout) as *mut Header;
+
+        if header.is_null() {
+            handle_alloc_error(layout)
+        }
+
+        // "Infinite" capacity for zero-sized types:
+        (*header).set_cap(if mem::size_of::<T>() == 0 {
+            MAX_CAP
+        } else {
+            cap
+        });
+        (*header).set_len(0);
+
+        NonNull::new_unchecked(header)
+    }
+}
+
+/// See the crate's top level documentation for a description of this type.
+#[repr(C)]
+pub struct ThinVec<T> {
+    ptr: NonNull<Header>,
+    boo: PhantomData<T>,
+}
+
+unsafe impl<T: Sync> Sync for ThinVec<T> {}
+unsafe impl<T: Send> Send for ThinVec<T> {}
+
+/// Creates a `ThinVec` containing the arguments.
+///
+/// ```
+/// #[macro_use] extern crate thin_vec;
+///
+/// fn main() {
+///     let v = thin_vec![1, 2, 3];
+///     assert_eq!(v.len(), 3);
+///     assert_eq!(v[0], 1);
+///     assert_eq!(v[1], 2);
+///     assert_eq!(v[2], 3);
+///
+///     let v = thin_vec![1; 3];
+///     assert_eq!(v, [1, 1, 1]);
+/// }
+/// ```
+#[macro_export]
+macro_rules! thin_vec {
+    (@UNIT $($t:tt)*) => (());
+
+    ($elem:expr; $n:expr) => ({
+        let mut vec = $crate::ThinVec::new();
+        vec.resize($n, $elem);
+        vec
+    });
+    () => {$crate::ThinVec::new()};
+    ($($x:expr),*) => ({
+        let len = [$(thin_vec!(@UNIT $x)),*].len();
+        let mut vec = $crate::ThinVec::with_capacity(len);
+        $(vec.push($x);)*
+        vec
+    });
+    ($($x:expr,)*) => (thin_vec![$($x),*]);
+}
+
+impl<T> ThinVec<T> {
+    pub fn new() -> ThinVec<T> {
+        ThinVec::with_capacity(0)
+    }
+
+    pub fn with_capacity(cap: usize) -> ThinVec<T> {
+        // `padding` contains ~static assertions against types that are
+        // incompatible with the current feature flags. We also call it to
+        // invoke these assertions when getting a pointer to the `ThinVec`
+        // contents, but since we also get a pointer to the contents in the
+        // `Drop` impl, trippng an assertion along that code path causes a
+        // double panic. We duplicate the assertion here so that it is
+        // testable,
+        let _ = padding::<T>();
+
+        if cap == 0 {
+            unsafe {
+                ThinVec {
+                    ptr: NonNull::new_unchecked(&EMPTY_HEADER as *const Header as *mut Header),
+                    boo: PhantomData,
+                }
+            }
+        } else {
+            ThinVec {
+                ptr: header_with_capacity::<T>(cap),
+                boo: PhantomData,
+            }
+        }
+    }
+
+    // Accessor conveniences
+
+    fn ptr(&self) -> *mut Header {
+        self.ptr.as_ptr()
+    }
+    fn header(&self) -> &Header {
+        unsafe { self.ptr.as_ref() }
+    }
+    fn data_raw(&self) -> *mut T {
+        // `padding` contains ~static assertions against types that are
+        // incompatible with the current feature flags. Even if we don't
+        // care about its result, we should always call it before getting
+        // a data pointer to guard against invalid types!
+        let padding = padding::<T>();
+
+        // Although we ensure the data array is aligned when we allocate,
+        // we can't do that with the empty singleton. So when it might not
+        // be properly aligned, we substitute in the NonNull::dangling
+        // which *is* aligned.
+        //
+        // To minimize dynamic branches on `cap` for all accesses
+        // to the data, we include this guard which should only involve
+        // compile-time constants. Ideally this should result in the branch
+        // only be included for types with excessive alignment.
+        let empty_header_is_aligned = if cfg!(feature = "gecko-ffi") {
+            // in gecko-ffi mode `padding` will ensure this under
+            // the assumption that the header has size 8 and the
+            // static empty singleton is aligned to 8.
+            true
+        } else {
+            // In non-gecko-ffi mode, the empty singleton is just
+            // naturally aligned to the Header. If the Header is at
+            // least as aligned as T *and* the padding would have
+            // been 0, then one-past-the-end of the empty singleton
+            // *is* a valid data pointer and we can remove the
+            // `dangling` special case.
+            mem::align_of::<Header>() >= mem::align_of::<T>() && padding == 0
+        };
+
+        unsafe {
+            if !empty_header_is_aligned && self.header().cap() == 0 {
+                NonNull::dangling().as_ptr()
+            } else {
+                // This could technically result in overflow, but padding
+                // would have to be absurdly large for this to occur.
+                let header_size = mem::size_of::<Header>();
+                let ptr = self.ptr.as_ptr() as *mut u8;
+                ptr.add(header_size + padding) as *mut T
+            }
+        }
+    }
+
+    // This is unsafe when the header is EMPTY_HEADER.
+    unsafe fn header_mut(&mut self) -> &mut Header {
+        &mut *self.ptr()
+    }
+
+    pub fn len(&self) -> usize {
+        self.header().len()
+    }
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+    pub fn capacity(&self) -> usize {
+        self.header().cap()
+    }
+
+    pub unsafe fn set_len(&mut self, len: usize) {
+        if self.is_singleton() {
+            // A prerequisite of `Vec::set_len` is that `new_len` must be
+            // less than or equal to capacity(). The same applies here.
+            assert!(len == 0, "invalid set_len({}) on empty ThinVec", len);
+        } else {
+            self.header_mut().set_len(len)
+        }
+    }
+
+    // For internal use only, when setting the length and it's known to be the non-singleton.
+    unsafe fn set_len_non_singleton(&mut self, len: usize) {
+        self.header_mut().set_len(len)
+    }
+
+    pub fn push(&mut self, val: T) {
+        let old_len = self.len();
+        if old_len == self.capacity() {
+            self.reserve(1);
+        }
+        unsafe {
+            ptr::write(self.data_raw().add(old_len), val);
+            self.set_len_non_singleton(old_len + 1);
+        }
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        let old_len = self.len();
+        if old_len == 0 {
+            return None;
+        }
+
+        unsafe {
+            self.set_len_non_singleton(old_len - 1);
+            Some(ptr::read(self.data_raw().add(old_len - 1)))
+        }
+    }
+
+    pub fn insert(&mut self, idx: usize, elem: T) {
+        let old_len = self.len();
+
+        assert!(idx <= old_len, "Index out of bounds");
+        if old_len == self.capacity() {
+            self.reserve(1);
+        }
+        unsafe {
+            let ptr = self.data_raw();
+            ptr::copy(ptr.add(idx), ptr.add(idx + 1), old_len - idx);
+            ptr::write(ptr.add(idx), elem);
+            self.set_len_non_singleton(old_len + 1);
+        }
+    }
+
+    pub fn remove(&mut self, idx: usize) -> T {
+        let old_len = self.len();
+
+        assert!(idx < old_len, "Index out of bounds");
+
+        unsafe {
+            self.set_len_non_singleton(old_len - 1);
+            let ptr = self.data_raw();
+            let val = ptr::read(self.data_raw().add(idx));
+            ptr::copy(ptr.add(idx + 1), ptr.add(idx), old_len - idx - 1);
+            val
+        }
+    }
+
+    pub fn swap_remove(&mut self, idx: usize) -> T {
+        let old_len = self.len();
+
+        assert!(idx < old_len, "Index out of bounds");
+
+        unsafe {
+            let ptr = self.data_raw();
+            ptr::swap(ptr.add(idx), ptr.add(old_len - 1));
+            self.set_len_non_singleton(old_len - 1);
+            ptr::read(ptr.add(old_len - 1))
+        }
+    }
+
+    pub fn truncate(&mut self, len: usize) {
+        unsafe {
+            // drop any extra elements
+            while len < self.len() {
+                // decrement len before the drop_in_place(), so a panic on Drop
+                // doesn't re-drop the just-failed value.
+                let new_len = self.len() - 1;
+                self.set_len_non_singleton(new_len);
+                ptr::drop_in_place(self.data_raw().add(new_len));
+            }
+        }
+    }
+
+    pub fn clear(&mut self) {
+        unsafe {
+            ptr::drop_in_place(&mut self[..]);
+            self.set_len(0); // could be the singleton
+        }
+    }
+
+    pub fn as_slice(&self) -> &[T] {
+        unsafe { slice::from_raw_parts(self.data_raw(), self.len()) }
+    }
+
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        unsafe { slice::from_raw_parts_mut(self.data_raw(), self.len()) }
+    }
+
+    /// Reserve capacity for at least `additional` more elements to be inserted.
+    ///
+    /// May reserve more space than requested, to avoid frequent reallocations.
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// Re-allocates only if `self.capacity() < self.len() + additional`.
+    #[cfg(not(feature = "gecko-ffi"))]
+    pub fn reserve(&mut self, additional: usize) {
+        let len = self.len();
+        let old_cap = self.capacity();
+        let min_cap = len.checked_add(additional).expect("capacity overflow");
+        if min_cap <= old_cap {
+            return;
+        }
+        // Ensure the new capacity is at least double, to guarantee exponential growth.
+        let double_cap = if old_cap == 0 {
+            // skip to 4 because tiny ThinVecs are dumb; but not if that would cause overflow
+            if mem::size_of::<T>() > (!0) / 8 {
+                1
+            } else {
+                4
+            }
+        } else {
+            old_cap.saturating_mul(2)
+        };
+        let new_cap = max(min_cap, double_cap);
+        unsafe {
+            self.reallocate(new_cap);
+        }
+    }
+
+    /// Reserve capacity for at least `additional` more elements to be inserted.
+    ///
+    /// This method mimics the growth algorithm used by the C++ implementation
+    /// of nsTArray.
+    #[cfg(feature = "gecko-ffi")]
+    pub fn reserve(&mut self, additional: usize) {
+        let elem_size = mem::size_of::<T>();
+
+        let len = self.len();
+        let old_cap = self.capacity();
+        let min_cap = len.checked_add(additional).expect("capacity overflow");
+        if min_cap <= old_cap {
+            return;
+        }
+
+        // The growth logic can't handle zero-sized types, so we have to exit
+        // early here.
+        if elem_size == 0 {
+            unsafe {
+                self.reallocate(min_cap);
+            }
+            return;
+        }
+
+        let min_cap_bytes = assert_size(min_cap)
+            .checked_mul(assert_size(elem_size))
+            .and_then(|x| x.checked_add(assert_size(mem::size_of::<Header>())))
+            .unwrap();
+
+        // Perform some checked arithmetic to ensure all of the numbers we
+        // compute will end up in range.
+        let will_fit = min_cap_bytes.checked_mul(2).is_some();
+        if !will_fit {
+            panic!("Exceeded maximum nsTArray size");
+        }
+
+        const SLOW_GROWTH_THRESHOLD: usize = 8 * 1024 * 1024;
+
+        let bytes = if min_cap > SLOW_GROWTH_THRESHOLD {
+            // Grow by a minimum of 1.125x
+            let old_cap_bytes = old_cap * elem_size + mem::size_of::<Header>();
+            let min_growth = old_cap_bytes + (old_cap_bytes >> 3);
+            let growth = max(min_growth, min_cap_bytes as usize);
+
+            // Round up to the next megabyte.
+            const MB: usize = 1 << 20;
+            MB * ((growth + MB - 1) / MB)
+        } else {
+            // Try to allocate backing buffers in powers of two.
+            min_cap_bytes.next_power_of_two() as usize
+        };
+
+        let cap = (bytes - std::mem::size_of::<Header>()) / elem_size;
+        unsafe {
+            self.reallocate(cap);
+        }
+    }
+
+    /// Reserves the minimum capacity for `additional` more elements to be inserted.
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// Re-allocates only if `self.capacity() < self.len() + additional`.
+    pub fn reserve_exact(&mut self, additional: usize) {
+        let new_cap = self
+            .len()
+            .checked_add(additional)
+            .expect("capacity overflow");
+        let old_cap = self.capacity();
+        if new_cap > old_cap {
+            unsafe {
+                self.reallocate(new_cap);
+            }
+        }
+    }
+
+    pub fn shrink_to_fit(&mut self) {
+        let old_cap = self.capacity();
+        let new_cap = self.len();
+        if new_cap < old_cap {
+            if new_cap == 0 {
+                *self = ThinVec::new();
+            } else {
+                unsafe {
+                    self.reallocate(new_cap);
+                }
+            }
+        }
+    }
+
+    /// Retains only the elements specified by the predicate.
+    ///
+    /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
+    /// This method operates in place and preserves the order of the retained
+    /// elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[macro_use] extern crate thin_vec;
+    /// # fn main() {
+    /// let mut vec = thin_vec![1, 2, 3, 4];
+    /// vec.retain(|&x| x%2 == 0);
+    /// assert_eq!(vec, [2, 4]);
+    /// # }
+    /// ```
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(&T) -> bool,
+    {
+        let len = self.len();
+        let mut del = 0;
+        {
+            let v = &mut self[..];
+
+            for i in 0..len {
+                if !f(&v[i]) {
+                    del += 1;
+                } else if del > 0 {
+                    v.swap(i - del, i);
+                }
+            }
+        }
+        if del > 0 {
+            self.truncate(len - del);
+        }
+    }
+
+    /// Removes consecutive elements in the vector that resolve to the same key.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[macro_use] extern crate thin_vec;
+    /// # fn main() {
+    /// let mut vec = thin_vec![10, 20, 21, 30, 20];
+    ///
+    /// vec.dedup_by_key(|i| *i / 10);
+    ///
+    /// assert_eq!(vec, [10, 20, 30, 20]);
+    /// # }
+    /// ```
+    pub fn dedup_by_key<F, K>(&mut self, mut key: F)
+    where
+        F: FnMut(&mut T) -> K,
+        K: PartialEq<K>,
+    {
+        self.dedup_by(|a, b| key(a) == key(b))
+    }
+
+    /// Removes consecutive elements in the vector according to a predicate.
+    ///
+    /// The `same_bucket` function is passed references to two elements from the vector, and
+    /// returns `true` if the elements compare equal, or `false` if they do not. Only the first
+    /// of adjacent equal items is kept.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[macro_use] extern crate thin_vec;
+    /// # fn main() {
+    /// let mut vec = thin_vec!["foo", "bar", "Bar", "baz", "bar"];
+    ///
+    /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
+    ///
+    /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
+    /// # }
+    /// ```
+    #[allow(clippy::swap_ptr_to_ref)]
+    pub fn dedup_by<F>(&mut self, mut same_bucket: F)
+    where
+        F: FnMut(&mut T, &mut T) -> bool,
+    {
+        // See the comments in `Vec::dedup` for a detailed explanation of this code.
+        unsafe {
+            let ln = self.len();
+            if ln <= 1 {
+                return;
+            }
+
+            // Avoid bounds checks by using raw pointers.
+            let p = self.as_mut_ptr();
+            let mut r: usize = 1;
+            let mut w: usize = 1;
+
+            while r < ln {
+                let p_r = p.add(r);
+                let p_wm1 = p.add(w - 1);
+                if !same_bucket(&mut *p_r, &mut *p_wm1) {
+                    if r != w {
+                        let p_w = p_wm1.add(1);
+                        mem::swap(&mut *p_r, &mut *p_w);
+                    }
+                    w += 1;
+                }
+                r += 1;
+            }
+
+            self.truncate(w);
+        }
+    }
+
+    pub fn split_off(&mut self, at: usize) -> ThinVec<T> {
+        let old_len = self.len();
+        let new_vec_len = old_len - at;
+
+        assert!(at <= old_len, "Index out of bounds");
+
+        unsafe {
+            let mut new_vec = ThinVec::with_capacity(new_vec_len);
+
+            ptr::copy_nonoverlapping(self.data_raw().add(at), new_vec.data_raw(), new_vec_len);
+
+            new_vec.set_len(new_vec_len); // could be the singleton
+            self.set_len(at); // could be the singleton
+
+            new_vec
+        }
+    }
+
+    pub fn append(&mut self, other: &mut ThinVec<T>) {
+        self.extend(other.drain(..))
+    }
+
+    pub fn drain<R>(&mut self, range: R) -> Drain<'_, T>
+    where
+        R: RangeBounds<usize>,
+    {
+        let len = self.len();
+        let start = match range.start_bound() {
+            Bound::Included(&n) => n,
+            Bound::Excluded(&n) => n + 1,
+            Bound::Unbounded => 0,
+        };
+        let end = match range.end_bound() {
+            Bound::Included(&n) => n + 1,
+            Bound::Excluded(&n) => n,
+            Bound::Unbounded => len,
+        };
+        assert!(start <= end);
+        assert!(end <= len);
+
+        unsafe {
+            // Set our length to the start bound
+            self.set_len(start); // could be the singleton
+
+            let iter =
+                slice::from_raw_parts_mut(self.data_raw().add(start), end - start).iter_mut();
+
+            Drain {
+                iter,
+                vec: self,
+                end,
+                tail: len - end,
+            }
+        }
+    }
+
+    unsafe fn deallocate(&mut self) {
+        if self.has_allocation() {
+            dealloc(self.ptr() as *mut u8, layout::<T>(self.capacity()))
+        }
+    }
+
+    /// Resize the buffer and update its capacity, without changing the length.
+    /// Unsafe because it can cause length to be greater than capacity.
+    unsafe fn reallocate(&mut self, new_cap: usize) {
+        debug_assert!(new_cap > 0);
+        if self.has_allocation() {
+            let old_cap = self.capacity();
+            let ptr = realloc(
+                self.ptr() as *mut u8,
+                layout::<T>(old_cap),
+                alloc_size::<T>(new_cap),
+            ) as *mut Header;
+
+            if ptr.is_null() {
+                handle_alloc_error(layout::<T>(new_cap))
+            }
+            (*ptr).set_cap(new_cap);
+            self.ptr = NonNull::new_unchecked(ptr);
+        } else {
+            let new_header = header_with_capacity::<T>(new_cap);
+
+            // If we get here and have a non-zero len, then we must be handling
+            // a gecko auto array, and we have items in a stack buffer. We shouldn't
+            // free it, but we should memcopy the contents out of it and mark it as empty.
+            //
+            // T is assumed to be trivially relocatable, as this is ~required
+            // for Rust compatibility anyway. Furthermore, we assume C++ won't try
+            // to unconditionally destroy the contents of the stack allocated buffer
+            // (i.e. it's obfuscated behind a union).
+            //
+            // In effect, we are partially reimplementing the auto array move constructor
+            // by leaving behind a valid empty instance.
+            let len = self.len();
+            if cfg!(feature = "gecko-ffi") && len > 0 {
+                new_header
+                    .as_ptr()
+                    .add(1)
+                    .cast::<T>()
+                    .copy_from_nonoverlapping(self.data_raw(), len);
+                self.set_len_non_singleton(0);
+            }
+
+            self.ptr = new_header;
+        }
+    }
+
+    #[cfg(feature = "gecko-ffi")]
+    #[inline]
+    fn is_singleton(&self) -> bool {
+        unsafe { self.ptr.as_ptr() as *const Header == &EMPTY_HEADER }
+    }
+
+    #[cfg(not(feature = "gecko-ffi"))]
+    #[inline]
+    fn is_singleton(&self) -> bool {
+        self.ptr.as_ptr() as *const Header == &EMPTY_HEADER
+    }
+
+    #[cfg(feature = "gecko-ffi")]
+    #[inline]
+    fn has_allocation(&self) -> bool {
+        unsafe { !self.is_singleton() && !self.ptr.as_ref().uses_stack_allocated_buffer() }
+    }
+
+    #[cfg(not(feature = "gecko-ffi"))]
+    #[inline]
+    fn has_allocation(&self) -> bool {
+        !self.is_singleton()
+    }
+}
+
+impl<T: Clone> ThinVec<T> {
+    /// Resizes the `Vec` in-place so that `len()` is equal to `new_len`.
+    ///
+    /// If `new_len` is greater than `len()`, the `Vec` is extended by the
+    /// difference, with each additional slot filled with `value`.
+    /// If `new_len` is less than `len()`, the `Vec` is simply truncated.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[macro_use] extern crate thin_vec;
+    /// # fn main() {
+    /// let mut vec = thin_vec!["hello"];
+    /// vec.resize(3, "world");
+    /// assert_eq!(vec, ["hello", "world", "world"]);
+    ///
+    /// let mut vec = thin_vec![1, 2, 3, 4];
+    /// vec.resize(2, 0);
+    /// assert_eq!(vec, [1, 2]);
+    /// # }
+    /// ```
+    pub fn resize(&mut self, new_len: usize, value: T) {
+        let old_len = self.len();
+
+        if new_len > old_len {
+            let additional = new_len - old_len;
+            self.reserve(additional);
+            for _ in 1..additional {
+                self.push(value.clone());
+            }
+            // We can write the last element directly without cloning needlessly
+            if additional > 0 {
+                self.push(value);
+            }
+        } else if new_len < old_len {
+            self.truncate(new_len);
+        }
+    }
+
+    pub fn extend_from_slice(&mut self, other: &[T]) {
+        self.extend(other.iter().cloned())
+    }
+}
+
+impl<T: PartialEq> ThinVec<T> {
+    /// Removes consecutive repeated elements in the vector.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #[macro_use] extern crate thin_vec;
+    /// # fn main() {
+    /// let mut vec = thin_vec![1, 2, 2, 3, 2];
+    ///
+    /// vec.dedup();
+    ///
+    /// assert_eq!(vec, [1, 2, 3, 2]);
+    /// # }
+    /// ```
+    pub fn dedup(&mut self) {
+        self.dedup_by(|a, b| a == b)
+    }
+}
+
+impl<T> Drop for ThinVec<T> {
+    fn drop(&mut self) {
+        unsafe {
+            ptr::drop_in_place(&mut self[..]);
+            self.deallocate();
+        }
+    }
+}
+
+impl<T> Deref for ThinVec<T> {
+    type Target = [T];
+
+    fn deref(&self) -> &[T] {
+        self.as_slice()
+    }
+}
+
+impl<T> DerefMut for ThinVec<T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        self.as_mut_slice()
+    }
+}
+
+impl<T> Borrow<[T]> for ThinVec<T> {
+    fn borrow(&self) -> &[T] {
+        self.as_slice()
+    }
+}
+
+impl<T> BorrowMut<[T]> for ThinVec<T> {
+    fn borrow_mut(&mut self) -> &mut [T] {
+        self.as_mut_slice()
+    }
+}
+
+impl<T> AsRef<[T]> for ThinVec<T> {
+    fn as_ref(&self) -> &[T] {
+        self.as_slice()
+    }
+}
+
+impl<T> Extend<T> for ThinVec<T> {
+    #[inline]
+    fn extend<I>(&mut self, iter: I)
+    where
+        I: IntoIterator<Item = T>,
+    {
+        let iter = iter.into_iter();
+        self.reserve(iter.size_hint().0);
+        for x in iter {
+            self.push(x);
+        }
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for ThinVec<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T> Hash for ThinVec<T>
+where
+    T: Hash,
+{
+    fn hash<H>(&self, state: &mut H)
+    where
+        H: Hasher,
+    {
+        self[..].hash(state);
+    }
+}
+
+impl<T> PartialOrd for ThinVec<T>
+where
+    T: PartialOrd,
+{
+    #[inline]
+    fn partial_cmp(&self, other: &ThinVec<T>) -> Option<Ordering> {
+        self[..].partial_cmp(&other[..])
+    }
+}
+
+impl<T> Ord for ThinVec<T>
+where
+    T: Ord,
+{
+    #[inline]
+    fn cmp(&self, other: &ThinVec<T>) -> Ordering {
+        self[..].cmp(&other[..])
+    }
+}
+
+impl<A, B> PartialEq<ThinVec<B>> for ThinVec<A>
+where
+    A: PartialEq<B>,
+{
+    #[inline]
+    fn eq(&self, other: &ThinVec<B>) -> bool {
+        self[..] == other[..]
+    }
+}
+
+impl<A, B> PartialEq<Vec<B>> for ThinVec<A>
+where
+    A: PartialEq<B>,
+{
+    #[inline]
+    fn eq(&self, other: &Vec<B>) -> bool {
+        self[..] == other[..]
+    }
+}
+
+impl<A, B> PartialEq<[B]> for ThinVec<A>
+where
+    A: PartialEq<B>,
+{
+    #[inline]
+    fn eq(&self, other: &[B]) -> bool {
+        self[..] == other[..]
+    }
+}
+
+impl<'a, A, B> PartialEq<&'a [B]> for ThinVec<A>
+where
+    A: PartialEq<B>,
+{
+    #[inline]
+    fn eq(&self, other: &&'a [B]) -> bool {
+        self[..] == other[..]
+    }
+}
+
+// Serde impls based on
+// https://github.com/bluss/arrayvec/blob/67ec907a98c0f40c4b76066fed3c1af59d35cf6a/src/arrayvec.rs#L1222-L1267
+#[cfg(feature = "serde")]
+impl<T: serde::Serialize> serde::Serialize for ThinVec<T> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.collect_seq(self.as_slice())
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de, T: serde::Deserialize<'de>> serde::Deserialize<'de> for ThinVec<T> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        use serde::de::{SeqAccess, Visitor};
+        use serde::Deserialize;
+
+        struct ThinVecVisitor<T>(PhantomData<T>);
+
+        impl<'de, T: Deserialize<'de>> Visitor<'de> for ThinVecVisitor<T> {
+            type Value = ThinVec<T>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                write!(formatter, "a sequence")
+            }
+
+            fn visit_seq<SA>(self, mut seq: SA) -> Result<Self::Value, SA::Error>
+            where
+                SA: SeqAccess<'de>,
+            {
+                // Same policy as
+                // https://github.com/serde-rs/serde/blob/ce0844b9ecc32377b5e4545d759d385a8c46bc6a/serde/src/private/size_hint.rs#L13
+                let initial_capacity = seq.size_hint().unwrap_or_default().min(4096);
+                let mut values = ThinVec::<T>::with_capacity(initial_capacity);
+
+                while let Some(value) = seq.next_element()? {
+                    values.push(value);
+                }
+
+                Ok(values)
+            }
+        }
+
+        deserializer.deserialize_seq(ThinVecVisitor::<T>(PhantomData))
+    }
+}
+
+macro_rules! array_impls {
+    ($($N:expr)*) => {$(
+        impl<A, B> PartialEq<[B; $N]> for ThinVec<A> where A: PartialEq<B> {
+            #[inline]
+            fn eq(&self, other: &[B; $N]) -> bool { self[..] == other[..] }
+        }
+
+        impl<'a, A, B> PartialEq<&'a [B; $N]> for ThinVec<A> where A: PartialEq<B> {
+            #[inline]
+            fn eq(&self, other: &&'a [B; $N]) -> bool { self[..] == other[..] }
+        }
+    )*}
+}
+
+array_impls! {
+    0  1  2  3  4  5  6  7  8  9
+    10 11 12 13 14 15 16 17 18 19
+    20 21 22 23 24 25 26 27 28 29
+    30 31 32
+}
+
+impl<T> Eq for ThinVec<T> where T: Eq {}
+
+impl<T> IntoIterator for ThinVec<T> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    fn into_iter(self) -> IntoIter<T> {
+        IntoIter {
+            vec: self,
+            start: 0,
+        }
+    }
+}
+
+impl<'a, T> IntoIterator for &'a ThinVec<T> {
+    type Item = &'a T;
+    type IntoIter = slice::Iter<'a, T>;
+
+    fn into_iter(self) -> slice::Iter<'a, T> {
+        self.iter()
+    }
+}
+
+impl<'a, T> IntoIterator for &'a mut ThinVec<T> {
+    type Item = &'a mut T;
+    type IntoIter = slice::IterMut<'a, T>;
+
+    fn into_iter(self) -> slice::IterMut<'a, T> {
+        self.iter_mut()
+    }
+}
+
+impl<T> Clone for ThinVec<T>
+where
+    T: Clone,
+{
+    fn clone(&self) -> ThinVec<T> {
+        let len = self.len();
+        let mut new_vec = ThinVec::<T>::with_capacity(len);
+        let mut data_raw = new_vec.data_raw();
+        for x in self.iter() {
+            unsafe {
+                ptr::write(data_raw, x.clone());
+                data_raw = data_raw.add(1);
+            }
+        }
+        unsafe {
+            new_vec.set_len(len); // could be the singleton
+        }
+        new_vec
+    }
+}
+
+impl<T> Default for ThinVec<T> {
+    fn default() -> ThinVec<T> {
+        ThinVec::new()
+    }
+}
+
+impl<T> FromIterator<T> for ThinVec<T> {
+    #[inline]
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> ThinVec<T> {
+        let mut vec = ThinVec::new();
+        vec.extend(iter.into_iter());
+        vec
+    }
+}
+
+pub struct IntoIter<T> {
+    vec: ThinVec<T>,
+    start: usize,
+}
+
+pub struct Drain<'a, T> {
+    iter: IterMut<'a, T>,
+    vec: *mut ThinVec<T>,
+    end: usize,
+    tail: usize,
+}
+
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+    fn next(&mut self) -> Option<T> {
+        if self.start == self.vec.len() {
+            None
+        } else {
+            unsafe {
+                let old_start = self.start;
+                self.start += 1;
+                Some(ptr::read(self.vec.data_raw().add(old_start)))
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.vec.len() - self.start;
+        (len, Some(len))
+    }
+}
+
+impl<T> DoubleEndedIterator for IntoIter<T> {
+    fn next_back(&mut self) -> Option<T> {
+        if self.start == self.vec.len() {
+            None
+        } else {
+            // FIXME?: extra bounds check
+            self.vec.pop()
+        }
+    }
+}
+
+impl<T> Drop for IntoIter<T> {
+    fn drop(&mut self) {
+        unsafe {
+            let mut vec = mem::replace(&mut self.vec, ThinVec::new());
+            ptr::drop_in_place(&mut vec[self.start..]);
+            vec.set_len(0) // could be the singleton
+        }
+    }
+}
+
+impl<'a, T> Iterator for Drain<'a, T> {
+    type Item = T;
+    fn next(&mut self) -> Option<T> {
+        self.iter.next().map(|x| unsafe { ptr::read(x) })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
+    fn next_back(&mut self) -> Option<T> {
+        self.iter.next_back().map(|x| unsafe { ptr::read(x) })
+    }
+}
+
+impl<'a, T> ExactSizeIterator for Drain<'a, T> {}
+
+impl<'a, T> Drop for Drain<'a, T> {
+    fn drop(&mut self) {
+        // Consume the rest of the iterator.
+        for _ in self.by_ref() {}
+
+        // Move the tail over the drained items, and update the length.
+        unsafe {
+            let vec = &mut *self.vec;
+
+            // Don't mutate the empty singleton!
+            if !vec.is_singleton() {
+                let old_len = vec.len();
+                let start = vec.data_raw().add(old_len);
+                let end = vec.data_raw().add(self.end);
+                ptr::copy(end, start, self.tail);
+                vec.set_len_non_singleton(old_len + self.tail);
+            }
+        }
+    }
+}
+
+/// Write is implemented for `ThinVec<u8>` by appending to the vector.
+/// The vector will grow as needed.
+/// This implementation is identical to the one for `Vec<u8>`.
+impl io::Write for ThinVec<u8> {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.extend_from_slice(buf);
+        Ok(buf.len())
+    }
+
+    #[inline]
+    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
+        self.extend_from_slice(buf);
+        Ok(())
+    }
+
+    #[inline]
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+// TODO: a million Index impls
+
+#[cfg(test)]
+mod tests {
+    use super::{ThinVec, MAX_CAP};
+
+    #[test]
+    fn test_size_of() {
+        use std::mem::size_of;
+        assert_eq!(size_of::<ThinVec<u8>>(), size_of::<&u8>());
+
+        assert_eq!(size_of::<Option<ThinVec<u8>>>(), size_of::<&u8>());
+    }
+
+    #[test]
+    fn test_drop_empty() {
+        ThinVec::<u8>::new();
+    }
+
+    #[test]
+    fn test_data_ptr_alignment() {
+        let v = ThinVec::<u16>::new();
+        assert!(v.data_raw() as usize % 2 == 0);
+
+        let v = ThinVec::<u32>::new();
+        assert!(v.data_raw() as usize % 4 == 0);
+
+        let v = ThinVec::<u64>::new();
+        assert!(v.data_raw() as usize % 8 == 0);
+    }
+
+    #[test]
+    #[cfg_attr(feature = "gecko-ffi", should_panic)]
+    fn test_overaligned_type_is_rejected_for_gecko_ffi_mode() {
+        #[repr(align(16))]
+        struct Align16(u8);
+
+        let v = ThinVec::<Align16>::new();
+        assert!(v.data_raw() as usize % 16 == 0);
+    }
+
+    #[test]
+    fn test_partial_eq() {
+        assert_eq!(thin_vec![0], thin_vec![0]);
+        assert_ne!(thin_vec![0], thin_vec![1]);
+        assert_eq!(thin_vec![1, 2, 3], vec![1, 2, 3]);
+    }
+
+    #[test]
+    fn test_alloc() {
+        let mut v = ThinVec::new();
+        assert!(!v.has_allocation());
+        v.push(1);
+        assert!(v.has_allocation());
+        v.pop();
+        assert!(v.has_allocation());
+        v.shrink_to_fit();
+        assert!(!v.has_allocation());
+        v.reserve(64);
+        assert!(v.has_allocation());
+        v = ThinVec::with_capacity(64);
+        assert!(v.has_allocation());
+        v = ThinVec::with_capacity(0);
+        assert!(!v.has_allocation());
+    }
+
+    #[test]
+    fn test_drain_items() {
+        let mut vec = thin_vec![1, 2, 3];
+        let mut vec2 = thin_vec![];
+        for i in vec.drain(..) {
+            vec2.push(i);
+        }
+        assert_eq!(vec, []);
+        assert_eq!(vec2, [1, 2, 3]);
+    }
+
+    #[test]
+    fn test_drain_items_reverse() {
+        let mut vec = thin_vec![1, 2, 3];
+        let mut vec2 = thin_vec![];
+        for i in vec.drain(..).rev() {
+            vec2.push(i);
+        }
+        assert_eq!(vec, []);
+        assert_eq!(vec2, [3, 2, 1]);
+    }
+
+    #[test]
+    fn test_drain_items_zero_sized() {
+        let mut vec = thin_vec![(), (), ()];
+        let mut vec2 = thin_vec![];
+        for i in vec.drain(..) {
+            vec2.push(i);
+        }
+        assert_eq!(vec, []);
+        assert_eq!(vec2, [(), (), ()]);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_drain_out_of_bounds() {
+        let mut v = thin_vec![1, 2, 3, 4, 5];
+        v.drain(5..6);
+    }
+
+    #[test]
+    fn test_drain_range() {
+        let mut v = thin_vec![1, 2, 3, 4, 5];
+        for _ in v.drain(4..) {}
+        assert_eq!(v, &[1, 2, 3, 4]);
+
+        let mut v: ThinVec<_> = (1..6).map(|x| x.to_string()).collect();
+        for _ in v.drain(1..4) {}
+        assert_eq!(v, &[1.to_string(), 5.to_string()]);
+
+        let mut v: ThinVec<_> = (1..6).map(|x| x.to_string()).collect();
+        for _ in v.drain(1..4).rev() {}
+        assert_eq!(v, &[1.to_string(), 5.to_string()]);
+
+        let mut v: ThinVec<_> = thin_vec![(); 5];
+        for _ in v.drain(1..4).rev() {}
+        assert_eq!(v, &[(), ()]);
+    }
+
+    #[test]
+    fn test_drain_max_vec_size() {
+        let mut v = ThinVec::<()>::with_capacity(MAX_CAP);
+        unsafe {
+            v.set_len(MAX_CAP);
+        }
+        for _ in v.drain(MAX_CAP - 1..) {}
+        assert_eq!(v.len(), MAX_CAP - 1);
+    }
+
+    #[test]
+    fn test_clear() {
+        let mut v = ThinVec::<i32>::new();
+        assert_eq!(v.len(), 0);
+        assert_eq!(v.capacity(), 0);
+        assert_eq!(&v[..], &[]);
+
+        v.clear();
+        assert_eq!(v.len(), 0);
+        assert_eq!(v.capacity(), 0);
+        assert_eq!(&v[..], &[]);
+
+        v.push(1);
+        v.push(2);
+        assert_eq!(v.len(), 2);
+        assert!(v.capacity() >= 2);
+        assert_eq!(&v[..], &[1, 2]);
+
+        v.clear();
+        assert_eq!(v.len(), 0);
+        assert!(v.capacity() >= 2);
+        assert_eq!(&v[..], &[]);
+
+        v.push(3);
+        v.push(4);
+        assert_eq!(v.len(), 2);
+        assert!(v.capacity() >= 2);
+        assert_eq!(&v[..], &[3, 4]);
+
+        v.clear();
+        assert_eq!(v.len(), 0);
+        assert!(v.capacity() >= 2);
+        assert_eq!(&v[..], &[]);
+
+        v.clear();
+        assert_eq!(v.len(), 0);
+        assert!(v.capacity() >= 2);
+        assert_eq!(&v[..], &[]);
+    }
+
+    #[test]
+    fn test_empty_singleton_torture() {
+        {
+            let mut v = ThinVec::<i32>::new();
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert!(v.is_empty());
+            assert_eq!(&v[..], &[]);
+            assert_eq!(&mut v[..], &mut []);
+
+            assert_eq!(v.pop(), None);
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let v = ThinVec::<i32>::new();
+            assert_eq!(v.into_iter().count(), 0);
+
+            let v = ThinVec::<i32>::new();
+            for _ in v.into_iter() {
+                unreachable!();
+            }
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            assert_eq!(v.drain(..).len(), 0);
+
+            for _ in v.drain(..) {
+                unreachable!()
+            }
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.truncate(1);
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+
+            v.truncate(0);
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.shrink_to_fit();
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            let new = v.split_off(0);
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+
+            assert_eq!(new.len(), 0);
+            assert_eq!(new.capacity(), 0);
+            assert_eq!(&new[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            let mut other = ThinVec::<i32>::new();
+            v.append(&mut other);
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+
+            assert_eq!(other.len(), 0);
+            assert_eq!(other.capacity(), 0);
+            assert_eq!(&other[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.reserve(0);
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.reserve_exact(0);
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.reserve(0);
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let v = ThinVec::<i32>::with_capacity(0);
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let v = ThinVec::<i32>::default();
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.retain(|_| unreachable!());
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.dedup_by_key(|x| *x);
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+
+        {
+            let mut v = ThinVec::<i32>::new();
+            v.dedup_by(|_, _| unreachable!());
+
+            assert_eq!(v.len(), 0);
+            assert_eq!(v.capacity(), 0);
+            assert_eq!(&v[..], &[]);
+        }
+    }
+}
+
+#[cfg(test)]
+mod std_tests {
+    #![allow(clippy::reversed_empty_ranges)]
+
+    use super::*;
+    use std::mem::size_of;
+    use std::usize;
+
+    struct DropCounter<'a> {
+        count: &'a mut u32,
+    }
+
+    impl<'a> Drop for DropCounter<'a> {
+        fn drop(&mut self) {
+            *self.count += 1;
+        }
+    }
+
+    #[test]
+    fn test_small_vec_struct() {
+        assert!(size_of::<ThinVec<u8>>() == size_of::<usize>());
+    }
+
+    #[test]
+    fn test_double_drop() {
+        struct TwoVec<T> {
+            x: ThinVec<T>,
+            y: ThinVec<T>,
+        }
+
+        let (mut count_x, mut count_y) = (0, 0);
+        {
+            let mut tv = TwoVec {
+                x: ThinVec::new(),
+                y: ThinVec::new(),
+            };
+            tv.x.push(DropCounter {
+                count: &mut count_x,
+            });
+            tv.y.push(DropCounter {
+                count: &mut count_y,
+            });
+
+            // If ThinVec had a drop flag, here is where it would be zeroed.
+            // Instead, it should rely on its internal state to prevent
+            // doing anything significant when dropped multiple times.
+            drop(tv.x);
+
+            // Here tv goes out of scope, tv.y should be dropped, but not tv.x.
+        }
+
+        assert_eq!(count_x, 1);
+        assert_eq!(count_y, 1);
+    }
+
+    #[test]
+    fn test_reserve() {
+        let mut v = ThinVec::new();
+        assert_eq!(v.capacity(), 0);
+
+        v.reserve(2);
+        assert!(v.capacity() >= 2);
+
+        for i in 0..16 {
+            v.push(i);
+        }
+
+        assert!(v.capacity() >= 16);
+        v.reserve(16);
+        assert!(v.capacity() >= 32);
+
+        v.push(16);
+
+        v.reserve(16);
+        assert!(v.capacity() >= 33)
+    }
+
+    #[test]
+    fn test_extend() {
+        let mut v = ThinVec::<usize>::new();
+        let mut w = ThinVec::new();
+        v.extend(w.clone());
+        assert_eq!(v, &[]);
+
+        v.extend(0..3);
+        for i in 0..3 {
+            w.push(i)
+        }
+
+        assert_eq!(v, w);
+
+        v.extend(3..10);
+        for i in 3..10 {
+            w.push(i)
+        }
+
+        assert_eq!(v, w);
+
+        v.extend(w.clone()); // specializes to `append`
+        assert!(v.iter().eq(w.iter().chain(w.iter())));
+
+        // Zero sized types
+        #[derive(PartialEq, Debug)]
+        struct Foo;
+
+        let mut a = ThinVec::new();
+        let b = thin_vec![Foo, Foo];
+
+        a.extend(b);
+        assert_eq!(a, &[Foo, Foo]);
+
+        // Double drop
+        let mut count_x = 0;
+        {
+            let mut x = ThinVec::new();
+            let y = thin_vec![DropCounter {
+                count: &mut count_x
+            }];
+            x.extend(y);
+        }
+
+        assert_eq!(count_x, 1);
+    }
+
+    /* TODO: implement extend for Iter<&Copy>
+        #[test]
+        fn test_extend_ref() {
+            let mut v = thin_vec![1, 2];
+            v.extend(&[3, 4, 5]);
+
+            assert_eq!(v.len(), 5);
+            assert_eq!(v, [1, 2, 3, 4, 5]);
+
+            let w = thin_vec![6, 7];
+            v.extend(&w);
+
+            assert_eq!(v.len(), 7);
+            assert_eq!(v, [1, 2, 3, 4, 5, 6, 7]);
+        }
+    */
+
+    #[test]
+    fn test_slice_from_mut() {
+        let mut values = thin_vec![1, 2, 3, 4, 5];
+        {
+            let slice = &mut values[2..];
+            assert!(slice == [3, 4, 5]);
+            for p in slice {
+                *p += 2;
+            }
+        }
+
+        assert!(values == [1, 2, 5, 6, 7]);
+    }
+
+    #[test]
+    fn test_slice_to_mut() {
+        let mut values = thin_vec![1, 2, 3, 4, 5];
+        {
+            let slice = &mut values[..2];
+            assert!(slice == [1, 2]);
+            for p in slice {
+                *p += 1;
+            }
+        }
+
+        assert!(values == [2, 3, 3, 4, 5]);
+    }
+
+    #[test]
+    fn test_split_at_mut() {
+        let mut values = thin_vec![1, 2, 3, 4, 5];
+        {
+            let (left, right) = values.split_at_mut(2);
+            {
+                let left: &[_] = left;
+                assert!(left[..left.len()] == [1, 2]);
+            }
+            for p in left {
+                *p += 1;
+            }
+
+            {
+                let right: &[_] = right;
+                assert!(right[..right.len()] == [3, 4, 5]);
+            }
+            for p in right {
+                *p += 2;
+            }
+        }
+
+        assert_eq!(values, [2, 3, 5, 6, 7]);
+    }
+
+    #[test]
+    fn test_clone() {
+        let v: ThinVec<i32> = thin_vec![];
+        let w = thin_vec![1, 2, 3];
+
+        assert_eq!(v, v.clone());
+
+        let z = w.clone();
+        assert_eq!(w, z);
+        // they should be disjoint in memory.
+        assert!(w.as_ptr() != z.as_ptr())
+    }
+
+    #[test]
+    fn test_clone_from() {
+        let mut v = thin_vec![];
+        let three: ThinVec<Box<_>> = thin_vec![Box::new(1), Box::new(2), Box::new(3)];
+        let two: ThinVec<Box<_>> = thin_vec![Box::new(4), Box::new(5)];
+        // zero, long
+        v.clone_from(&three);
+        assert_eq!(v, three);
+
+        // equal
+        v.clone_from(&three);
+        assert_eq!(v, three);
+
+        // long, short
+        v.clone_from(&two);
+        assert_eq!(v, two);
+
+        // short, long
+        v.clone_from(&three);
+        assert_eq!(v, three)
+    }
+
+    #[test]
+    fn test_retain() {
+        let mut vec = thin_vec![1, 2, 3, 4];
+        vec.retain(|&x| x % 2 == 0);
+        assert_eq!(vec, [2, 4]);
+    }
+
+    #[test]
+    fn test_dedup() {
+        fn case(a: ThinVec<i32>, b: ThinVec<i32>) {
+            let mut v = a;
+            v.dedup();
+            assert_eq!(v, b);
+        }
+        case(thin_vec![], thin_vec![]);
+        case(thin_vec![1], thin_vec![1]);
+        case(thin_vec![1, 1], thin_vec![1]);
+        case(thin_vec![1, 2, 3], thin_vec![1, 2, 3]);
+        case(thin_vec![1, 1, 2, 3], thin_vec![1, 2, 3]);
+        case(thin_vec![1, 2, 2, 3], thin_vec![1, 2, 3]);
+        case(thin_vec![1, 2, 3, 3], thin_vec![1, 2, 3]);
+        case(thin_vec![1, 1, 2, 2, 2, 3, 3], thin_vec![1, 2, 3]);
+    }
+
+    #[test]
+    fn test_dedup_by_key() {
+        fn case(a: ThinVec<i32>, b: ThinVec<i32>) {
+            let mut v = a;
+            v.dedup_by_key(|i| *i / 10);
+            assert_eq!(v, b);
+        }
+        case(thin_vec![], thin_vec![]);
+        case(thin_vec![10], thin_vec![10]);
+        case(thin_vec![10, 11], thin_vec![10]);
+        case(thin_vec![10, 20, 30], thin_vec![10, 20, 30]);
+        case(thin_vec![10, 11, 20, 30], thin_vec![10, 20, 30]);
+        case(thin_vec![10, 20, 21, 30], thin_vec![10, 20, 30]);
+        case(thin_vec![10, 20, 30, 31], thin_vec![10, 20, 30]);
+        case(thin_vec![10, 11, 20, 21, 22, 30, 31], thin_vec![10, 20, 30]);
+    }
+
+    #[test]
+    fn test_dedup_by() {
+        let mut vec = thin_vec!["foo", "bar", "Bar", "baz", "bar"];
+        vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
+
+        assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
+
+        let mut vec = thin_vec![("foo", 1), ("foo", 2), ("bar", 3), ("bar", 4), ("bar", 5)];
+        vec.dedup_by(|a, b| {
+            a.0 == b.0 && {
+                b.1 += a.1;
+                true
+            }
+        });
+
+        assert_eq!(vec, [("foo", 3), ("bar", 12)]);
+    }
+
+    #[test]
+    fn test_dedup_unique() {
+        let mut v0: ThinVec<Box<_>> = thin_vec![Box::new(1), Box::new(1), Box::new(2), Box::new(3)];
+        v0.dedup();
+        let mut v1: ThinVec<Box<_>> = thin_vec![Box::new(1), Box::new(2), Box::new(2), Box::new(3)];
+        v1.dedup();
+        let mut v2: ThinVec<Box<_>> = thin_vec![Box::new(1), Box::new(2), Box::new(3), Box::new(3)];
+        v2.dedup();
+        // If the boxed pointers were leaked or otherwise misused, valgrind
+        // and/or rt should raise errors.
+    }
+
+    #[test]
+    fn zero_sized_values() {
+        let mut v = ThinVec::new();
+        assert_eq!(v.len(), 0);
+        v.push(());
+        assert_eq!(v.len(), 1);
+        v.push(());
+        assert_eq!(v.len(), 2);
+        assert_eq!(v.pop(), Some(()));
+        assert_eq!(v.pop(), Some(()));
+        assert_eq!(v.pop(), None);
+
+        assert_eq!(v.iter().count(), 0);
+        v.push(());
+        assert_eq!(v.iter().count(), 1);
+        v.push(());
+        assert_eq!(v.iter().count(), 2);
+
+        for &() in &v {}
+
+        assert_eq!(v.iter_mut().count(), 2);
+        v.push(());
+        assert_eq!(v.iter_mut().count(), 3);
+        v.push(());
+        assert_eq!(v.iter_mut().count(), 4);
+
+        for &mut () in &mut v {}
+        unsafe {
+            v.set_len(0);
+        }
+        assert_eq!(v.iter_mut().count(), 0);
+    }
+
+    #[test]
+    fn test_partition() {
+        assert_eq!(
+            thin_vec![].into_iter().partition(|x: &i32| *x < 3),
+            (thin_vec![], thin_vec![])
+        );
+        assert_eq!(
+            thin_vec![1, 2, 3].into_iter().partition(|x| *x < 4),
+            (thin_vec![1, 2, 3], thin_vec![])
+        );
+        assert_eq!(
+            thin_vec![1, 2, 3].into_iter().partition(|x| *x < 2),
+            (thin_vec![1], thin_vec![2, 3])
+        );
+        assert_eq!(
+            thin_vec![1, 2, 3].into_iter().partition(|x| *x < 0),
+            (thin_vec![], thin_vec![1, 2, 3])
+        );
+    }
+
+    #[test]
+    fn test_zip_unzip() {
+        let z1 = thin_vec![(1, 4), (2, 5), (3, 6)];
+
+        let (left, right): (ThinVec<_>, ThinVec<_>) = z1.iter().cloned().unzip();
+
+        assert_eq!((1, 4), (left[0], right[0]));
+        assert_eq!((2, 5), (left[1], right[1]));
+        assert_eq!((3, 6), (left[2], right[2]));
+    }
+
+    #[test]
+    fn test_vec_truncate_drop() {
+        static mut DROPS: u32 = 0;
+        struct Elem(i32);
+        impl Drop for Elem {
+            fn drop(&mut self) {
+                unsafe {
+                    DROPS += 1;
+                }
+            }
+        }
+
+        let mut v = thin_vec![Elem(1), Elem(2), Elem(3), Elem(4), Elem(5)];
+        assert_eq!(unsafe { DROPS }, 0);
+        v.truncate(3);
+        assert_eq!(unsafe { DROPS }, 2);
+        v.truncate(0);
+        assert_eq!(unsafe { DROPS }, 5);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_vec_truncate_fail() {
+        struct BadElem(i32);
+        impl Drop for BadElem {
+            fn drop(&mut self) {
+                let BadElem(ref mut x) = *self;
+                if *x == 0xbadbeef {
+                    panic!("BadElem panic: 0xbadbeef")
+                }
+            }
+        }
+
+        let mut v = thin_vec![BadElem(1), BadElem(2), BadElem(0xbadbeef), BadElem(4)];
+        v.truncate(0);
+    }
+
+    #[test]
+    fn test_index() {
+        let vec = thin_vec![1, 2, 3];
+        assert!(vec[1] == 2);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_index_out_of_bounds() {
+        let vec = thin_vec![1, 2, 3];
+        let _ = vec[3];
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_slice_out_of_bounds_1() {
+        let x = thin_vec![1, 2, 3, 4, 5];
+        let _ = &x[!0..];
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_slice_out_of_bounds_2() {
+        let x = thin_vec![1, 2, 3, 4, 5];
+        let _ = &x[..6];
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_slice_out_of_bounds_3() {
+        let x = thin_vec![1, 2, 3, 4, 5];
+        let _ = &x[!0..4];
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_slice_out_of_bounds_4() {
+        let x = thin_vec![1, 2, 3, 4, 5];
+        let _ = &x[1..6];
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_slice_out_of_bounds_5() {
+        let x = thin_vec![1, 2, 3, 4, 5];
+        let _ = &x[3..2];
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_swap_remove_empty() {
+        let mut vec = ThinVec::<i32>::new();
+        vec.swap_remove(0);
+    }
+
+    #[test]
+    fn test_move_items() {
+        let vec = thin_vec![1, 2, 3];
+        let mut vec2 = thin_vec![];
+        for i in vec {
+            vec2.push(i);
+        }
+        assert_eq!(vec2, [1, 2, 3]);
+    }
+
+    #[test]
+    fn test_move_items_reverse() {
+        let vec = thin_vec![1, 2, 3];
+        let mut vec2 = thin_vec![];
+        for i in vec.into_iter().rev() {
+            vec2.push(i);
+        }
+        assert_eq!(vec2, [3, 2, 1]);
+    }
+
+    #[test]
+    fn test_move_items_zero_sized() {
+        let vec = thin_vec![(), (), ()];
+        let mut vec2 = thin_vec![];
+        for i in vec {
+            vec2.push(i);
+        }
+        assert_eq!(vec2, [(), (), ()]);
+    }
+
+    #[test]
+    fn test_drain_items() {
+        let mut vec = thin_vec![1, 2, 3];
+        let mut vec2 = thin_vec![];
+        for i in vec.drain(..) {
+            vec2.push(i);
+        }
+        assert_eq!(vec, []);
+        assert_eq!(vec2, [1, 2, 3]);
+    }
+
+    #[test]
+    fn test_drain_items_reverse() {
+        let mut vec = thin_vec![1, 2, 3];
+        let mut vec2 = thin_vec![];
+        for i in vec.drain(..).rev() {
+            vec2.push(i);
+        }
+        assert_eq!(vec, []);
+        assert_eq!(vec2, [3, 2, 1]);
+    }
+
+    #[test]
+    fn test_drain_items_zero_sized() {
+        let mut vec = thin_vec![(), (), ()];
+        let mut vec2 = thin_vec![];
+        for i in vec.drain(..) {
+            vec2.push(i);
+        }
+        assert_eq!(vec, []);
+        assert_eq!(vec2, [(), (), ()]);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_drain_out_of_bounds() {
+        let mut v = thin_vec![1, 2, 3, 4, 5];
+        v.drain(5..6);
+    }
+
+    #[test]
+    fn test_drain_range() {
+        let mut v = thin_vec![1, 2, 3, 4, 5];
+        for _ in v.drain(4..) {}
+        assert_eq!(v, &[1, 2, 3, 4]);
+
+        let mut v: ThinVec<_> = (1..6).map(|x| x.to_string()).collect();
+        for _ in v.drain(1..4) {}
+        assert_eq!(v, &[1.to_string(), 5.to_string()]);
+
+        let mut v: ThinVec<_> = (1..6).map(|x| x.to_string()).collect();
+        for _ in v.drain(1..4).rev() {}
+        assert_eq!(v, &[1.to_string(), 5.to_string()]);
+
+        let mut v: ThinVec<_> = thin_vec![(); 5];
+        for _ in v.drain(1..4).rev() {}
+        assert_eq!(v, &[(), ()]);
+    }
+
+    #[test]
+    fn test_drain_inclusive_range() {
+        let mut v = thin_vec!['a', 'b', 'c', 'd', 'e'];
+        for _ in v.drain(1..=3) {}
+        assert_eq!(v, &['a', 'e']);
+
+        let mut v: ThinVec<_> = (0..=5).map(|x| x.to_string()).collect();
+        for _ in v.drain(1..=5) {}
+        assert_eq!(v, &["0".to_string()]);
+
+        let mut v: ThinVec<String> = (0..=5).map(|x| x.to_string()).collect();
+        for _ in v.drain(0..=5) {}
+        assert_eq!(v, ThinVec::<String>::new());
+
+        let mut v: ThinVec<_> = (0..=5).map(|x| x.to_string()).collect();
+        for _ in v.drain(0..=3) {}
+        assert_eq!(v, &["4".to_string(), "5".to_string()]);
+
+        let mut v: ThinVec<_> = (0..=1).map(|x| x.to_string()).collect();
+        for _ in v.drain(..=0) {}
+        assert_eq!(v, &["1".to_string()]);
+    }
+
+    #[test]
+    #[cfg(not(feature = "gecko-ffi"))]
+    fn test_drain_max_vec_size() {
+        let mut v = ThinVec::<()>::with_capacity(usize::max_value());
+        unsafe {
+            v.set_len(usize::max_value());
+        }
+        for _ in v.drain(usize::max_value() - 1..) {}
+        assert_eq!(v.len(), usize::max_value() - 1);
+
+        let mut v = ThinVec::<()>::with_capacity(usize::max_value());
+        unsafe {
+            v.set_len(usize::max_value());
+        }
+        for _ in v.drain(usize::max_value() - 1..=usize::max_value() - 1) {}
+        assert_eq!(v.len(), usize::max_value() - 1);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_drain_inclusive_out_of_bounds() {
+        let mut v = thin_vec![1, 2, 3, 4, 5];
+        v.drain(5..=5);
+    }
+
+    /* TODO: implement splice?
+        #[test]
+        fn test_splice() {
+            let mut v = thin_vec![1, 2, 3, 4, 5];
+            let a = [10, 11, 12];
+            v.splice(2..4, a.iter().cloned());
+            assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
+            v.splice(1..3, Some(20));
+            assert_eq!(v, &[1, 20, 11, 12, 5]);
+        }
+
+        #[test]
+        fn test_splice_inclusive_range() {
+            let mut v = thin_vec![1, 2, 3, 4, 5];
+            let a = [10, 11, 12];
+            let t1: ThinVec<_> = v.splice(2..=3, a.iter().cloned()).collect();
+            assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
+            assert_eq!(t1, &[3, 4]);
+            let t2: ThinVec<_> = v.splice(1..=2, Some(20)).collect();
+            assert_eq!(v, &[1, 20, 11, 12, 5]);
+            assert_eq!(t2, &[2, 10]);
+        }
+
+        #[test]
+        #[should_panic]
+        fn test_splice_out_of_bounds() {
+            let mut v = thin_vec![1, 2, 3, 4, 5];
+            let a = [10, 11, 12];
+            v.splice(5..6, a.iter().cloned());
+        }
+
+        #[test]
+        #[should_panic]
+        fn test_splice_inclusive_out_of_bounds() {
+            let mut v = thin_vec![1, 2, 3, 4, 5];
+            let a = [10, 11, 12];
+            v.splice(5..=5, a.iter().cloned());
+        }
+
+        #[test]
+        fn test_splice_items_zero_sized() {
+            let mut vec = thin_vec![(), (), ()];
+            let vec2 = thin_vec![];
+            let t: ThinVec<_> = vec.splice(1..2, vec2.iter().cloned()).collect();
+            assert_eq!(vec, &[(), ()]);
+            assert_eq!(t, &[()]);
+        }
+
+        #[test]
+        fn test_splice_unbounded() {
+            let mut vec = thin_vec![1, 2, 3, 4, 5];
+            let t: ThinVec<_> = vec.splice(.., None).collect();
+            assert_eq!(vec, &[]);
+            assert_eq!(t, &[1, 2, 3, 4, 5]);
+        }
+
+        #[test]
+        fn test_splice_forget() {
+            let mut v = thin_vec![1, 2, 3, 4, 5];
+            let a = [10, 11, 12];
+            ::std::mem::forget(v.splice(2..4, a.iter().cloned()));
+            assert_eq!(v, &[1, 2]);
+        }
+    */
+
+    /* probs won't ever impl this
+        #[test]
+        fn test_into_boxed_slice() {
+            let xs = thin_vec![1, 2, 3];
+            let ys = xs.into_boxed_slice();
+            assert_eq!(&*ys, [1, 2, 3]);
+        }
+    */
+
+    #[test]
+    fn test_append() {
+        let mut vec = thin_vec![1, 2, 3];
+        let mut vec2 = thin_vec![4, 5, 6];
+        vec.append(&mut vec2);
+        assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
+        assert_eq!(vec2, []);
+    }
+
+    #[test]
+    fn test_split_off() {
+        let mut vec = thin_vec![1, 2, 3, 4, 5, 6];
+        let vec2 = vec.split_off(4);
+        assert_eq!(vec, [1, 2, 3, 4]);
+        assert_eq!(vec2, [5, 6]);
+    }
+
+    /* TODO: implement into_iter methods?
+        #[test]
+        fn test_into_iter_as_slice() {
+            let vec = thin_vec!['a', 'b', 'c'];
+            let mut into_iter = vec.into_iter();
+            assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
+            let _ = into_iter.next().unwrap();
+            assert_eq!(into_iter.as_slice(), &['b', 'c']);
+            let _ = into_iter.next().unwrap();
+            let _ = into_iter.next().unwrap();
+            assert_eq!(into_iter.as_slice(), &[]);
+        }
+
+        #[test]
+        fn test_into_iter_as_mut_slice() {
+            let vec = thin_vec!['a', 'b', 'c'];
+            let mut into_iter = vec.into_iter();
+            assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
+            into_iter.as_mut_slice()[0] = 'x';
+            into_iter.as_mut_slice()[1] = 'y';
+            assert_eq!(into_iter.next().unwrap(), 'x');
+            assert_eq!(into_iter.as_slice(), &['y', 'c']);
+        }
+
+        #[test]
+        fn test_into_iter_debug() {
+            let vec = thin_vec!['a', 'b', 'c'];
+            let into_iter = vec.into_iter();
+            let debug = format!("{:?}", into_iter);
+            assert_eq!(debug, "IntoIter(['a', 'b', 'c'])");
+        }
+
+        #[test]
+        fn test_into_iter_count() {
+            assert_eq!(thin_vec![1, 2, 3].into_iter().count(), 3);
+        }
+
+        #[test]
+        fn test_into_iter_clone() {
+            fn iter_equal<I: Iterator<Item = i32>>(it: I, slice: &[i32]) {
+                let v: ThinVec<i32> = it.collect();
+                assert_eq!(&v[..], slice);
+            }
+            let mut it = thin_vec![1, 2, 3].into_iter();
+            iter_equal(it.clone(), &[1, 2, 3]);
+            assert_eq!(it.next(), Some(1));
+            let mut it = it.rev();
+            iter_equal(it.clone(), &[3, 2]);
+            assert_eq!(it.next(), Some(3));
+            iter_equal(it.clone(), &[2]);
+            assert_eq!(it.next(), Some(2));
+            iter_equal(it.clone(), &[]);
+            assert_eq!(it.next(), None);
+        }
+    */
+
+    /* TODO: implement CoW interop?
+        #[test]
+        fn test_cow_from() {
+            let borrowed: &[_] = &["borrowed", "(slice)"];
+            let owned = thin_vec!["owned", "(vec)"];
+            match (Cow::from(owned.clone()), Cow::from(borrowed)) {
+                (Cow::Owned(o), Cow::Borrowed(b)) => assert!(o == owned && b == borrowed),
+                _ => panic!("invalid `Cow::from`"),
+            }
+        }
+
+        #[test]
+        fn test_from_cow() {
+            let borrowed: &[_] = &["borrowed", "(slice)"];
+            let owned = thin_vec!["owned", "(vec)"];
+            assert_eq!(ThinVec::from(Cow::Borrowed(borrowed)), thin_vec!["borrowed", "(slice)"]);
+            assert_eq!(ThinVec::from(Cow::Owned(owned)), thin_vec!["owned", "(vec)"]);
+        }
+    */
+
+    /* TODO: make drain covariant
+        #[allow(dead_code)]
+        fn assert_covariance() {
+            fn drain<'new>(d: Drain<'static, &'static str>) -> Drain<'new, &'new str> {
+                d
+            }
+            fn into_iter<'new>(i: IntoIter<&'static str>) -> IntoIter<&'new str> {
+                i
+            }
+        }
+    */
+
+    /* TODO: specialize vec.into_iter().collect::<ThinVec<_>>();
+        #[test]
+        fn from_into_inner() {
+            let vec = thin_vec![1, 2, 3];
+            let ptr = vec.as_ptr();
+            let vec = vec.into_iter().collect::<ThinVec<_>>();
+            assert_eq!(vec, [1, 2, 3]);
+            assert_eq!(vec.as_ptr(), ptr);
+
+            let ptr = &vec[1] as *const _;
+            let mut it = vec.into_iter();
+            it.next().unwrap();
+            let vec = it.collect::<ThinVec<_>>();
+            assert_eq!(vec, [2, 3]);
+            assert!(ptr != vec.as_ptr());
+        }
+    */
+
+    /* TODO: implement higher than 16 alignment
+        #[test]
+        fn overaligned_allocations() {
+            #[repr(align(256))]
+            struct Foo(usize);
+            let mut v = thin_vec![Foo(273)];
+            for i in 0..0x1000 {
+                v.reserve_exact(i);
+                assert!(v[0].0 == 273);
+                assert!(v.as_ptr() as usize & 0xff == 0);
+                v.shrink_to_fit();
+                assert!(v[0].0 == 273);
+                assert!(v.as_ptr() as usize & 0xff == 0);
+            }
+        }
+    */
+
+    /* TODO: implement drain_filter?
+        #[test]
+        fn drain_filter_empty() {
+            let mut vec: ThinVec<i32> = thin_vec![];
+
+            {
+                let mut iter = vec.drain_filter(|_| true);
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+                assert_eq!(iter.next(), None);
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+                assert_eq!(iter.next(), None);
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+            }
+            assert_eq!(vec.len(), 0);
+            assert_eq!(vec, thin_vec![]);
+        }
+
+        #[test]
+        fn drain_filter_zst() {
+            let mut vec = thin_vec![(), (), (), (), ()];
+            let initial_len = vec.len();
+            let mut count = 0;
+            {
+                let mut iter = vec.drain_filter(|_| true);
+                assert_eq!(iter.size_hint(), (0, Some(initial_len)));
+                while let Some(_) = iter.next() {
+                    count += 1;
+                    assert_eq!(iter.size_hint(), (0, Some(initial_len - count)));
+                }
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+                assert_eq!(iter.next(), None);
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+            }
+
+            assert_eq!(count, initial_len);
+            assert_eq!(vec.len(), 0);
+            assert_eq!(vec, thin_vec![]);
+        }
+
+        #[test]
+        fn drain_filter_false() {
+            let mut vec = thin_vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+            let initial_len = vec.len();
+            let mut count = 0;
+            {
+                let mut iter = vec.drain_filter(|_| false);
+                assert_eq!(iter.size_hint(), (0, Some(initial_len)));
+                for _ in iter.by_ref() {
+                    count += 1;
+                }
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+                assert_eq!(iter.next(), None);
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+            }
+
+            assert_eq!(count, 0);
+            assert_eq!(vec.len(), initial_len);
+            assert_eq!(vec, thin_vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
+        }
+
+        #[test]
+        fn drain_filter_true() {
+            let mut vec = thin_vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+            let initial_len = vec.len();
+            let mut count = 0;
+            {
+                let mut iter = vec.drain_filter(|_| true);
+                assert_eq!(iter.size_hint(), (0, Some(initial_len)));
+                while let Some(_) = iter.next() {
+                    count += 1;
+                    assert_eq!(iter.size_hint(), (0, Some(initial_len - count)));
+                }
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+                assert_eq!(iter.next(), None);
+                assert_eq!(iter.size_hint(), (0, Some(0)));
+            }
+
+            assert_eq!(count, initial_len);
+            assert_eq!(vec.len(), 0);
+            assert_eq!(vec, thin_vec![]);
+        }
+
+        #[test]
+        fn drain_filter_complex() {
+
+            {   //                [+xxx++++++xxxxx++++x+x++]
+                let mut vec = thin_vec![1,
+                                   2, 4, 6,
+                                   7, 9, 11, 13, 15, 17,
+                                   18, 20, 22, 24, 26,
+                                   27, 29, 31, 33,
+                                   34,
+                                   35,
+                                   36,
+                                   37, 39];
+
+                let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<ThinVec<_>>();
+                assert_eq!(removed.len(), 10);
+                assert_eq!(removed, thin_vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
+
+                assert_eq!(vec.len(), 14);
+                assert_eq!(vec, thin_vec![1, 7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39]);
+            }
+
+            {   //                [xxx++++++xxxxx++++x+x++]
+                let mut vec = thin_vec![2, 4, 6,
+                                   7, 9, 11, 13, 15, 17,
+                                   18, 20, 22, 24, 26,
+                                   27, 29, 31, 33,
+                                   34,
+                                   35,
+                                   36,
+                                   37, 39];
+
+                let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<ThinVec<_>>();
+                assert_eq!(removed.len(), 10);
+                assert_eq!(removed, thin_vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
+
+                assert_eq!(vec.len(), 13);
+                assert_eq!(vec, thin_vec![7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39]);
+            }
+
+            {   //                [xxx++++++xxxxx++++x+x]
+                let mut vec = thin_vec![2, 4, 6,
+                                   7, 9, 11, 13, 15, 17,
+                                   18, 20, 22, 24, 26,
+                                   27, 29, 31, 33,
+                                   34,
+                                   35,
+                                   36];
+
+                let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<ThinVec<_>>();
+                assert_eq!(removed.len(), 10);
+                assert_eq!(removed, thin_vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);
+
+                assert_eq!(vec.len(), 11);
+                assert_eq!(vec, thin_vec![7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35]);
+            }
+
+            {   //                [xxxxxxxxxx+++++++++++]
+                let mut vec = thin_vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20,
+                                   1, 3, 5, 7, 9, 11, 13, 15, 17, 19];
+
+                let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<ThinVec<_>>();
+                assert_eq!(removed.len(), 10);
+                assert_eq!(removed, thin_vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20]);
+
+                assert_eq!(vec.len(), 10);
+                assert_eq!(vec, thin_vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19]);
+            }
+
+            {   //                [+++++++++++xxxxxxxxxx]
+                let mut vec = thin_vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19,
+                                   2, 4, 6, 8, 10, 12, 14, 16, 18, 20];
+
+                let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<ThinVec<_>>();
+                assert_eq!(removed.len(), 10);
+                assert_eq!(removed, thin_vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20]);
+
+                assert_eq!(vec.len(), 10);
+                assert_eq!(vec, thin_vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19]);
+            }
+        }
+    */
+    #[test]
+    fn test_reserve_exact() {
+        // This is all the same as test_reserve
+
+        let mut v = ThinVec::new();
+        assert_eq!(v.capacity(), 0);
+
+        v.reserve_exact(2);
+        assert!(v.capacity() >= 2);
+
+        for i in 0..16 {
+            v.push(i);
+        }
+
+        assert!(v.capacity() >= 16);
+        v.reserve_exact(16);
+        assert!(v.capacity() >= 32);
+
+        v.push(16);
+
+        v.reserve_exact(16);
+        assert!(v.capacity() >= 33)
+    }
+
+    /* TODO: implement try_reserve
+        #[test]
+        fn test_try_reserve() {
+
+            // These are the interesting cases:
+            // * exactly isize::MAX should never trigger a CapacityOverflow (can be OOM)
+            // * > isize::MAX should always fail
+            //    * On 16/32-bit should CapacityOverflow
+            //    * On 64-bit should OOM
+            // * overflow may trigger when adding `len` to `cap` (in number of elements)
+            // * overflow may trigger when multiplying `new_cap` by size_of::<T> (to get bytes)
+
+            const MAX_CAP: usize = isize::MAX as usize;
+            const MAX_USIZE: usize = usize::MAX;
+
+            // On 16/32-bit, we check that allocations don't exceed isize::MAX,
+            // on 64-bit, we assume the OS will give an OOM for such a ridiculous size.
+            // Any platform that succeeds for these requests is technically broken with
+            // ptr::offset because LLVM is the worst.
+            let guards_against_isize = size_of::<usize>() < 8;
+
+            {
+                // Note: basic stuff is checked by test_reserve
+                let mut empty_bytes: ThinVec<u8> = ThinVec::new();
+
+                // Check isize::MAX doesn't count as an overflow
+                if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                // Play it again, frank! (just to be sure)
+                if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+
+                if guards_against_isize {
+                    // Check isize::MAX + 1 does count as overflow
+                    if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP + 1) {
+                    } else { panic!("isize::MAX + 1 should trigger an overflow!") }
+
+                    // Check usize::MAX does count as overflow
+                    if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE) {
+                    } else { panic!("usize::MAX should trigger an overflow!") }
+                } else {
+                    // Check isize::MAX + 1 is an OOM
+                    if let Err(AllocErr) = empty_bytes.try_reserve(MAX_CAP + 1) {
+                    } else { panic!("isize::MAX + 1 should trigger an OOM!") }
+
+                    // Check usize::MAX is an OOM
+                    if let Err(AllocErr) = empty_bytes.try_reserve(MAX_USIZE) {
+                    } else { panic!("usize::MAX should trigger an OOM!") }
+                }
+            }
+
+
+            {
+                // Same basic idea, but with non-zero len
+                let mut ten_bytes: ThinVec<u8> = thin_vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+                if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if guards_against_isize {
+                    if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
+                } else {
+                    if let Err(AllocErr) = ten_bytes.try_reserve(MAX_CAP - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an OOM!") }
+                }
+                // Should always overflow in the add-to-len
+                if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE) {
+                } else { panic!("usize::MAX should trigger an overflow!") }
+            }
+
+
+            {
+                // Same basic idea, but with interesting type size
+                let mut ten_u32s: ThinVec<u32> = thin_vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+                if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP/4 - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP/4 - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if guards_against_isize {
+                    if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
+                } else {
+                    if let Err(AllocErr) = ten_u32s.try_reserve(MAX_CAP/4 - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an OOM!") }
+                }
+                // Should fail in the mul-by-size
+                if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20) {
+                } else {
+                    panic!("usize::MAX should trigger an overflow!");
+                }
+            }
+
+        }
+
+        #[test]
+        fn test_try_reserve_exact() {
+
+            // This is exactly the same as test_try_reserve with the method changed.
+            // See that test for comments.
+
+            const MAX_CAP: usize = isize::MAX as usize;
+            const MAX_USIZE: usize = usize::MAX;
+
+            let guards_against_isize = size_of::<usize>() < 8;
+
+            {
+                let mut empty_bytes: ThinVec<u8> = ThinVec::new();
+
+                if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+
+                if guards_against_isize {
+                    if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
+                    } else { panic!("isize::MAX + 1 should trigger an overflow!") }
+
+                    if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_USIZE) {
+                    } else { panic!("usize::MAX should trigger an overflow!") }
+                } else {
+                    if let Err(AllocErr) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
+                    } else { panic!("isize::MAX + 1 should trigger an OOM!") }
+
+                    if let Err(AllocErr) = empty_bytes.try_reserve_exact(MAX_USIZE) {
+                    } else { panic!("usize::MAX should trigger an OOM!") }
+                }
+            }
+
+
+            {
+                let mut ten_bytes: ThinVec<u8> = thin_vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+                if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if guards_against_isize {
+                    if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
+                } else {
+                    if let Err(AllocErr) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an OOM!") }
+                }
+                if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
+                } else { panic!("usize::MAX should trigger an overflow!") }
+            }
+
+
+            {
+                let mut ten_u32s: ThinVec<u32> = thin_vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+
+                if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 10) {
+                    panic!("isize::MAX shouldn't trigger an overflow!");
+                }
+                if guards_against_isize {
+                    if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an overflow!"); }
+                } else {
+                    if let Err(AllocErr) = ten_u32s.try_reserve_exact(MAX_CAP/4 - 9) {
+                    } else { panic!("isize::MAX + 1 should trigger an OOM!") }
+                }
+                if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_USIZE - 20) {
+                } else { panic!("usize::MAX should trigger an overflow!") }
+            }
+        }
+    */
+
+    #[test]
+    #[cfg_attr(feature = "gecko-ffi", ignore)]
+    fn test_header_data() {
+        macro_rules! assert_aligned_head_ptr {
+            ($typename:ty) => {{
+                let v: ThinVec<$typename> = ThinVec::with_capacity(1 /* ensure allocation */);
+                let head_ptr: *mut $typename = v.data_raw();
+                assert_eq!(
+                    head_ptr as usize % std::mem::align_of::<$typename>(),
+                    0,
+                    "expected Header::data<{}> to be aligned",
+                    stringify!($typename)
+                );
+            }};
+        }
+
+        const HEADER_SIZE: usize = std::mem::size_of::<Header>();
+        assert_eq!(2 * std::mem::size_of::<usize>(), HEADER_SIZE);
+
+        #[repr(C, align(128))]
+        struct Funky<T>(T);
+        assert_eq!(padding::<Funky<()>>(), 128 - HEADER_SIZE);
+        assert_aligned_head_ptr!(Funky<()>);
+
+        assert_eq!(padding::<Funky<u8>>(), 128 - HEADER_SIZE);
+        assert_aligned_head_ptr!(Funky<u8>);
+
+        assert_eq!(padding::<Funky<[(); 1024]>>(), 128 - HEADER_SIZE);
+        assert_aligned_head_ptr!(Funky<[(); 1024]>);
+
+        assert_eq!(padding::<Funky<[*mut usize; 1024]>>(), 128 - HEADER_SIZE);
+        assert_aligned_head_ptr!(Funky<[*mut usize; 1024]>);
+    }
+
+    #[cfg(feature = "serde")]
+    use serde_test::{assert_tokens, Token};
+
+    #[test]
+    #[cfg(feature = "serde")]
+    fn test_ser_de_empty() {
+        let vec = ThinVec::<u32>::new();
+
+        assert_tokens(&vec, &[Token::Seq { len: Some(0) }, Token::SeqEnd]);
+    }
+
+    #[test]
+    #[cfg(feature = "serde")]
+    fn test_ser_de() {
+        let mut vec = ThinVec::<u32>::new();
+        vec.push(20);
+        vec.push(55);
+        vec.push(123);
+
+        assert_tokens(
+            &vec,
+            &[
+                Token::Seq { len: Some(3) },
+                Token::U32(20),
+                Token::U32(55),
+                Token::U32(123),
+                Token::SeqEnd,
+            ],
+        );
+    }
+
+    #[test]
+    fn test_set_len() {
+        let mut vec: ThinVec<u32> = thin_vec![];
+        unsafe {
+            vec.set_len(0); // at one point this caused a crash
+        }
+    }
+
+    #[test]
+    #[should_panic(expected = "invalid set_len(1) on empty ThinVec")]
+    fn test_set_len_invalid() {
+        let mut vec: ThinVec<u32> = thin_vec![];
+        unsafe {
+            vec.set_len(1);
+        }
+    }
+}