Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

7 files changed, 2204 insertions, 0 deletions

diff --git a/third_party/rust/arrayvec/src/array_string.rs b/third_party/rust/arrayvec/src/array_string.rs
new file mode 100644
index 0000000000..c4712a0cbe
--- /dev/null
+++ b/third_party/rust/arrayvec/src/array_string.rs
@@ -0,0 +1,640 @@
+use std::borrow::Borrow;
+use std::cmp;
+use std::convert::TryFrom;
+use std::fmt;
+use std::hash::{Hash, Hasher};
+use std::mem::MaybeUninit;
+use std::ops::{Deref, DerefMut};
+use std::ptr;
+use std::slice;
+use std::str;
+use std::str::FromStr;
+use std::str::Utf8Error;
+
+use crate::CapacityError;
+use crate::LenUint;
+use crate::char::encode_utf8;
+use crate::utils::MakeMaybeUninit;
+
+#[cfg(feature="serde")]
+use serde::{Serialize, Deserialize, Serializer, Deserializer};
+
+
+/// A string with a fixed capacity.
+///
+/// The `ArrayString` is a string backed by a fixed size array. It keeps track
+/// of its length, and is parameterized by `CAP` for the maximum capacity.
+///
+/// `CAP` is of type `usize` but is range limited to `u32::MAX`; attempting to create larger
+/// arrayvecs with larger capacity will panic.
+///
+/// The string is a contiguous value that you can store directly on the stack
+/// if needed.
+#[derive(Copy)]
+pub struct ArrayString<const CAP: usize> {
+    // the `len` first elements of the array are initialized
+    xs: [MaybeUninit<u8>; CAP],
+    len: LenUint,
+}
+
+impl<const CAP: usize> Default for ArrayString<CAP>
+{
+    /// Return an empty `ArrayString`
+    fn default() -> ArrayString<CAP> {
+        ArrayString::new()
+    }
+}
+
+impl<const CAP: usize> ArrayString<CAP>
+{
+    /// Create a new empty `ArrayString`.
+    ///
+    /// Capacity is inferred from the type parameter.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<16>::new();
+    /// string.push_str("foo");
+    /// assert_eq!(&string[..], "foo");
+    /// assert_eq!(string.capacity(), 16);
+    /// ```
+    pub fn new() -> ArrayString<CAP> {
+        assert_capacity_limit!(CAP);
+        unsafe {
+            ArrayString { xs: MaybeUninit::uninit().assume_init(), len: 0 }
+        }
+    }
+
+    /// Create a new empty `ArrayString` (const fn).
+    ///
+    /// Capacity is inferred from the type parameter.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// static ARRAY: ArrayString<1024> = ArrayString::new_const();
+    /// ```
+    pub const fn new_const() -> ArrayString<CAP> {
+        assert_capacity_limit_const!(CAP);
+        ArrayString { xs: MakeMaybeUninit::ARRAY, len: 0 }
+    }
+
+    /// Return the length of the string.
+    #[inline]
+    pub const fn len(&self) -> usize { self.len as usize }
+
+    /// Returns whether the string is empty.
+    #[inline]
+    pub const fn is_empty(&self) -> bool { self.len() == 0 }
+
+    /// Create a new `ArrayString` from a `str`.
+    ///
+    /// Capacity is inferred from the type parameter.
+    ///
+    /// **Errors** if the backing array is not large enough to fit the string.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<3>::from("foo").unwrap();
+    /// assert_eq!(&string[..], "foo");
+    /// assert_eq!(string.len(), 3);
+    /// assert_eq!(string.capacity(), 3);
+    /// ```
+    pub fn from(s: &str) -> Result<Self, CapacityError<&str>> {
+        let mut arraystr = Self::new();
+        arraystr.try_push_str(s)?;
+        Ok(arraystr)
+    }
+
+    /// Create a new `ArrayString` from a byte string literal.
+    ///
+    /// **Errors** if the byte string literal is not valid UTF-8.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let string = ArrayString::from_byte_string(b"hello world").unwrap();
+    /// ```
+    pub fn from_byte_string(b: &[u8; CAP]) -> Result<Self, Utf8Error> {
+        let len = str::from_utf8(b)?.len();
+        debug_assert_eq!(len, CAP);
+        let mut vec = Self::new();
+        unsafe {
+            (b as *const [u8; CAP] as *const [MaybeUninit<u8>; CAP])
+                .copy_to_nonoverlapping(&mut vec.xs as *mut [MaybeUninit<u8>; CAP], 1);
+            vec.set_len(CAP);
+        }
+        Ok(vec)
+    }
+
+    /// Create a new `ArrayString` value fully filled with ASCII NULL characters (`\0`). Useful
+    /// to be used as a buffer to collect external data or as a buffer for intermediate processing.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let string = ArrayString::<16>::zero_filled();
+    /// assert_eq!(string.len(), 16);
+    /// ```
+    #[inline]
+    pub fn zero_filled() -> Self {
+        assert_capacity_limit!(CAP);
+        // SAFETY: `assert_capacity_limit` asserts that `len` won't overflow and
+        // `zeroed` fully fills the array with nulls.
+        unsafe {
+            ArrayString {
+                xs: MaybeUninit::zeroed().assume_init(),
+                len: CAP as _
+            }
+        }
+    }
+
+    /// Return the capacity of the `ArrayString`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let string = ArrayString::<3>::new();
+    /// assert_eq!(string.capacity(), 3);
+    /// ```
+    #[inline(always)]
+    pub const fn capacity(&self) -> usize { CAP }
+
+    /// Return if the `ArrayString` is completely filled.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<1>::new();
+    /// assert!(!string.is_full());
+    /// string.push_str("A");
+    /// assert!(string.is_full());
+    /// ```
+    pub const fn is_full(&self) -> bool { self.len() == self.capacity() }
+
+    /// Returns the capacity left in the `ArrayString`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<3>::from("abc").unwrap();
+    /// string.pop();
+    /// assert_eq!(string.remaining_capacity(), 1);
+    /// ```
+    pub const fn remaining_capacity(&self) -> usize {
+        self.capacity() - self.len()
+    }
+
+    /// Adds the given char to the end of the string.
+    ///
+    /// ***Panics*** if the backing array is not large enough to fit the additional char.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<2>::new();
+    ///
+    /// string.push('a');
+    /// string.push('b');
+    ///
+    /// assert_eq!(&string[..], "ab");
+    /// ```
+    pub fn push(&mut self, c: char) {
+        self.try_push(c).unwrap();
+    }
+
+    /// Adds the given char to the end of the string.
+    ///
+    /// Returns `Ok` if the push succeeds.
+    ///
+    /// **Errors** if the backing array is not large enough to fit the additional char.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<2>::new();
+    ///
+    /// string.try_push('a').unwrap();
+    /// string.try_push('b').unwrap();
+    /// let overflow = string.try_push('c');
+    ///
+    /// assert_eq!(&string[..], "ab");
+    /// assert_eq!(overflow.unwrap_err().element(), 'c');
+    /// ```
+    pub fn try_push(&mut self, c: char) -> Result<(), CapacityError<char>> {
+        let len = self.len();
+        unsafe {
+            let ptr = self.as_mut_ptr().add(len);
+            let remaining_cap = self.capacity() - len;
+            match encode_utf8(c, ptr, remaining_cap) {
+                Ok(n) => {
+                    self.set_len(len + n);
+                    Ok(())
+                }
+                Err(_) => Err(CapacityError::new(c)),
+            }
+        }
+    }
+
+    /// Adds the given string slice to the end of the string.
+    ///
+    /// ***Panics*** if the backing array is not large enough to fit the string.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<2>::new();
+    ///
+    /// string.push_str("a");
+    /// string.push_str("d");
+    ///
+    /// assert_eq!(&string[..], "ad");
+    /// ```
+    pub fn push_str(&mut self, s: &str) {
+        self.try_push_str(s).unwrap()
+    }
+
+    /// Adds the given string slice to the end of the string.
+    ///
+    /// Returns `Ok` if the push succeeds.
+    ///
+    /// **Errors** if the backing array is not large enough to fit the string.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<2>::new();
+    ///
+    /// string.try_push_str("a").unwrap();
+    /// let overflow1 = string.try_push_str("bc");
+    /// string.try_push_str("d").unwrap();
+    /// let overflow2 = string.try_push_str("ef");
+    ///
+    /// assert_eq!(&string[..], "ad");
+    /// assert_eq!(overflow1.unwrap_err().element(), "bc");
+    /// assert_eq!(overflow2.unwrap_err().element(), "ef");
+    /// ```
+    pub fn try_push_str<'a>(&mut self, s: &'a str) -> Result<(), CapacityError<&'a str>> {
+        if s.len() > self.capacity() - self.len() {
+            return Err(CapacityError::new(s));
+        }
+        unsafe {
+            let dst = self.as_mut_ptr().add(self.len());
+            let src = s.as_ptr();
+            ptr::copy_nonoverlapping(src, dst, s.len());
+            let newl = self.len() + s.len();
+            self.set_len(newl);
+        }
+        Ok(())
+    }
+
+    /// Removes the last character from the string and returns it.
+    ///
+    /// Returns `None` if this `ArrayString` is empty.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    /// 
+    /// let mut s = ArrayString::<3>::from("foo").unwrap();
+    ///
+    /// assert_eq!(s.pop(), Some('o'));
+    /// assert_eq!(s.pop(), Some('o'));
+    /// assert_eq!(s.pop(), Some('f'));
+    ///
+    /// assert_eq!(s.pop(), None);
+    /// ```
+    pub fn pop(&mut self) -> Option<char> {
+        let ch = match self.chars().rev().next() {
+            Some(ch) => ch,
+            None => return None,
+        };
+        let new_len = self.len() - ch.len_utf8();
+        unsafe {
+            self.set_len(new_len);
+        }
+        Some(ch)
+    }
+
+    /// Shortens this `ArrayString` to the specified length.
+    ///
+    /// If `new_len` is greater than the string’s current length, this has no
+    /// effect.
+    ///
+    /// ***Panics*** if `new_len` does not lie on a `char` boundary.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    ///
+    /// let mut string = ArrayString::<6>::from("foobar").unwrap();
+    /// string.truncate(3);
+    /// assert_eq!(&string[..], "foo");
+    /// string.truncate(4);
+    /// assert_eq!(&string[..], "foo");
+    /// ```
+    pub fn truncate(&mut self, new_len: usize) {
+        if new_len <= self.len() {
+            assert!(self.is_char_boundary(new_len));
+            unsafe { 
+                // In libstd truncate is called on the underlying vector,
+                // which in turns drops each element.
+                // As we know we don't have to worry about Drop,
+                // we can just set the length (a la clear.)
+                self.set_len(new_len);
+            }
+        }
+    }
+
+    /// Removes a `char` from this `ArrayString` at a byte position and returns it.
+    ///
+    /// This is an `O(n)` operation, as it requires copying every element in the
+    /// array.
+    ///
+    /// ***Panics*** if `idx` is larger than or equal to the `ArrayString`’s length,
+    /// or if it does not lie on a `char` boundary.
+    ///
+    /// ```
+    /// use arrayvec::ArrayString;
+    /// 
+    /// let mut s = ArrayString::<3>::from("foo").unwrap();
+    ///
+    /// assert_eq!(s.remove(0), 'f');
+    /// assert_eq!(s.remove(1), 'o');
+    /// assert_eq!(s.remove(0), 'o');
+    /// ```
+    pub fn remove(&mut self, idx: usize) -> char {
+        let ch = match self[idx..].chars().next() {
+            Some(ch) => ch,
+            None => panic!("cannot remove a char from the end of a string"),
+        };
+
+        let next = idx + ch.len_utf8();
+        let len = self.len();
+        unsafe {
+            ptr::copy(self.as_ptr().add(next),
+                      self.as_mut_ptr().add(idx),
+                      len - next);
+            self.set_len(len - (next - idx));
+        }
+        ch
+    }
+
+    /// Make the string empty.
+    pub fn clear(&mut self) {
+        unsafe {
+            self.set_len(0);
+        }
+    }
+
+    /// Set the strings’s length.
+    ///
+    /// This function is `unsafe` because it changes the notion of the
+    /// number of “valid” bytes in the string. Use with care.
+    ///
+    /// This method uses *debug assertions* to check the validity of `length`
+    /// and may use other debug assertions.
+    pub unsafe fn set_len(&mut self, length: usize) {
+        // type invariant that capacity always fits in LenUint
+        debug_assert!(length <= self.capacity());
+        self.len = length as LenUint;
+    }
+
+    /// Return a string slice of the whole `ArrayString`.
+    pub fn as_str(&self) -> &str {
+        self
+    }
+
+    /// Return a mutable string slice of the whole `ArrayString`.
+    pub fn as_mut_str(&mut self) -> &mut str {
+        self
+    }
+
+    fn as_ptr(&self) -> *const u8 {
+        self.xs.as_ptr() as *const u8
+    }
+
+    fn as_mut_ptr(&mut self) -> *mut u8 {
+        self.xs.as_mut_ptr() as *mut u8
+    }
+}
+
+impl<const CAP: usize> Deref for ArrayString<CAP>
+{
+    type Target = str;
+    #[inline]
+    fn deref(&self) -> &str {
+        unsafe {
+            let sl = slice::from_raw_parts(self.as_ptr(), self.len());
+            str::from_utf8_unchecked(sl)
+        }
+    }
+}
+
+impl<const CAP: usize> DerefMut for ArrayString<CAP>
+{
+    #[inline]
+    fn deref_mut(&mut self) -> &mut str {
+        unsafe {
+            let len = self.len();
+            let sl = slice::from_raw_parts_mut(self.as_mut_ptr(), len);
+            str::from_utf8_unchecked_mut(sl)
+        }
+    }
+}
+
+impl<const CAP: usize> PartialEq for ArrayString<CAP>
+{
+    fn eq(&self, rhs: &Self) -> bool {
+        **self == **rhs
+    }
+}
+
+impl<const CAP: usize> PartialEq<str> for ArrayString<CAP>
+{
+    fn eq(&self, rhs: &str) -> bool {
+        &**self == rhs
+    }
+}
+
+impl<const CAP: usize> PartialEq<ArrayString<CAP>> for str
+{
+    fn eq(&self, rhs: &ArrayString<CAP>) -> bool {
+        self == &**rhs
+    }
+}
+
+impl<const CAP: usize> Eq for ArrayString<CAP> 
+{ }
+
+impl<const CAP: usize> Hash for ArrayString<CAP>
+{
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        (**self).hash(h)
+    }
+}
+
+impl<const CAP: usize> Borrow<str> for ArrayString<CAP>
+{
+    fn borrow(&self) -> &str { self }
+}
+
+impl<const CAP: usize> AsRef<str> for ArrayString<CAP>
+{
+    fn as_ref(&self) -> &str { self }
+}
+
+impl<const CAP: usize> fmt::Debug for ArrayString<CAP>
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { (**self).fmt(f) }
+}
+
+impl<const CAP: usize> fmt::Display for ArrayString<CAP>
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { (**self).fmt(f) }
+}
+
+/// `Write` appends written data to the end of the string.
+impl<const CAP: usize> fmt::Write for ArrayString<CAP>
+{
+    fn write_char(&mut self, c: char) -> fmt::Result {
+        self.try_push(c).map_err(|_| fmt::Error)
+    }
+
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.try_push_str(s).map_err(|_| fmt::Error)
+    }
+}
+
+impl<const CAP: usize> Clone for ArrayString<CAP>
+{
+    fn clone(&self) -> ArrayString<CAP> {
+        *self
+    }
+    fn clone_from(&mut self, rhs: &Self) {
+        // guaranteed to fit due to types matching.
+        self.clear();
+        self.try_push_str(rhs).ok();
+    }
+}
+
+impl<const CAP: usize> PartialOrd for ArrayString<CAP>
+{
+    fn partial_cmp(&self, rhs: &Self) -> Option<cmp::Ordering> {
+        (**self).partial_cmp(&**rhs)
+    }
+    fn lt(&self, rhs: &Self) -> bool { **self < **rhs }
+    fn le(&self, rhs: &Self) -> bool { **self <= **rhs }
+    fn gt(&self, rhs: &Self) -> bool { **self > **rhs }
+    fn ge(&self, rhs: &Self) -> bool { **self >= **rhs }
+}
+
+impl<const CAP: usize> PartialOrd<str> for ArrayString<CAP>
+{
+    fn partial_cmp(&self, rhs: &str) -> Option<cmp::Ordering> {
+        (**self).partial_cmp(rhs)
+    }
+    fn lt(&self, rhs: &str) -> bool { &**self < rhs }
+    fn le(&self, rhs: &str) -> bool { &**self <= rhs }
+    fn gt(&self, rhs: &str) -> bool { &**self > rhs }
+    fn ge(&self, rhs: &str) -> bool { &**self >= rhs }
+}
+
+impl<const CAP: usize> PartialOrd<ArrayString<CAP>> for str
+{
+    fn partial_cmp(&self, rhs: &ArrayString<CAP>) -> Option<cmp::Ordering> {
+        self.partial_cmp(&**rhs)
+    }
+    fn lt(&self, rhs: &ArrayString<CAP>) -> bool { self < &**rhs }
+    fn le(&self, rhs: &ArrayString<CAP>) -> bool { self <= &**rhs }
+    fn gt(&self, rhs: &ArrayString<CAP>) -> bool { self > &**rhs }
+    fn ge(&self, rhs: &ArrayString<CAP>) -> bool { self >= &**rhs }
+}
+
+impl<const CAP: usize> Ord for ArrayString<CAP>
+{
+    fn cmp(&self, rhs: &Self) -> cmp::Ordering {
+        (**self).cmp(&**rhs)
+    }
+}
+
+impl<const CAP: usize> FromStr for ArrayString<CAP>
+{
+    type Err = CapacityError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Self::from(s).map_err(CapacityError::simplify)
+    }
+}
+
+#[cfg(feature="serde")]
+/// Requires crate feature `"serde"`
+impl<const CAP: usize> Serialize for ArrayString<CAP>
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where S: Serializer
+    {
+        serializer.serialize_str(&*self)
+    }
+}
+
+#[cfg(feature="serde")]
+/// Requires crate feature `"serde"`
+impl<'de, const CAP: usize> Deserialize<'de> for ArrayString<CAP> 
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where D: Deserializer<'de>
+    {
+        use serde::de::{self, Visitor};
+        use std::marker::PhantomData;
+
+        struct ArrayStringVisitor<const CAP: usize>(PhantomData<[u8; CAP]>);
+
+        impl<'de, const CAP: usize> Visitor<'de> for ArrayStringVisitor<CAP> {
+            type Value = ArrayString<CAP>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                write!(formatter, "a string no more than {} bytes long", CAP)
+            }
+
+            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+                where E: de::Error,
+            {
+                ArrayString::from(v).map_err(|_| E::invalid_length(v.len(), &self))
+            }
+
+            fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+                where E: de::Error,
+            {
+                let s = str::from_utf8(v).map_err(|_| E::invalid_value(de::Unexpected::Bytes(v), &self))?;
+
+                ArrayString::from(s).map_err(|_| E::invalid_length(s.len(), &self))
+            }
+        }
+
+        deserializer.deserialize_str(ArrayStringVisitor(PhantomData))
+    }
+}
+
+impl<'a, const CAP: usize> TryFrom<&'a str> for ArrayString<CAP>
+{
+    type Error = CapacityError<&'a str>;
+
+    fn try_from(f: &'a str) -> Result<Self, Self::Error> {
+        let mut v = Self::new();
+        v.try_push_str(f)?;
+        Ok(v)
+    }
+}
+
+impl<'a, const CAP: usize> TryFrom<fmt::Arguments<'a>> for ArrayString<CAP>
+{
+    type Error = CapacityError<fmt::Error>;
+
+    fn try_from(f: fmt::Arguments<'a>) -> Result<Self, Self::Error> {
+        use fmt::Write;
+        let mut v = Self::new();
+        v.write_fmt(f).map_err(|e| CapacityError::new(e))?;
+        Ok(v)
+    }
+}
diff --git a/third_party/rust/arrayvec/src/arrayvec.rs b/third_party/rust/arrayvec/src/arrayvec.rs
new file mode 100644
index 0000000000..e69e60c180
--- /dev/null
+++ b/third_party/rust/arrayvec/src/arrayvec.rs
@@ -0,0 +1,1267 @@
+
+use std::cmp;
+use std::iter;
+use std::mem;
+use std::ops::{Bound, Deref, DerefMut, RangeBounds};
+use std::ptr;
+use std::slice;
+
+// extra traits
+use std::borrow::{Borrow, BorrowMut};
+use std::hash::{Hash, Hasher};
+use std::fmt;
+
+#[cfg(feature="std")]
+use std::io;
+
+use std::mem::ManuallyDrop;
+use std::mem::MaybeUninit;
+
+#[cfg(feature="serde")]
+use serde::{Serialize, Deserialize, Serializer, Deserializer};
+
+use crate::LenUint;
+use crate::errors::CapacityError;
+use crate::arrayvec_impl::ArrayVecImpl;
+use crate::utils::MakeMaybeUninit;
+
+/// A vector with a fixed capacity.
+///
+/// The `ArrayVec` is a vector backed by a fixed size array. It keeps track of
+/// the number of initialized elements. The `ArrayVec<T, CAP>` is parameterized
+/// by `T` for the element type and `CAP` for the maximum capacity.
+///
+/// `CAP` is of type `usize` but is range limited to `u32::MAX`; attempting to create larger
+/// arrayvecs with larger capacity will panic.
+///
+/// The vector is a contiguous value (storing the elements inline) that you can store directly on
+/// the stack if needed.
+///
+/// It offers a simple API but also dereferences to a slice, so that the full slice API is
+/// available. The ArrayVec can be converted into a by value iterator.
+pub struct ArrayVec<T, const CAP: usize> {
+    // the `len` first elements of the array are initialized
+    xs: [MaybeUninit<T>; CAP],
+    len: LenUint,
+}
+
+impl<T, const CAP: usize> Drop for ArrayVec<T, CAP> {
+    fn drop(&mut self) {
+        self.clear();
+
+        // MaybeUninit inhibits array's drop
+    }
+}
+
+macro_rules! panic_oob {
+    ($method_name:expr, $index:expr, $len:expr) => {
+        panic!(concat!("ArrayVec::", $method_name, ": index {} is out of bounds in vector of length {}"),
+               $index, $len)
+    }
+}
+
+impl<T, const CAP: usize> ArrayVec<T, CAP> {
+    /// Capacity
+    const CAPACITY: usize = CAP;
+
+    /// Create a new empty `ArrayVec`.
+    ///
+    /// The maximum capacity is given by the generic parameter `CAP`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 16>::new();
+    /// array.push(1);
+    /// array.push(2);
+    /// assert_eq!(&array[..], &[1, 2]);
+    /// assert_eq!(array.capacity(), 16);
+    /// ```
+    pub fn new() -> ArrayVec<T, CAP> {
+        assert_capacity_limit!(CAP);
+        unsafe {
+            ArrayVec { xs: MaybeUninit::uninit().assume_init(), len: 0 }
+        }
+    }
+
+    /// Create a new empty `ArrayVec` (const fn).
+    ///
+    /// The maximum capacity is given by the generic parameter `CAP`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// static ARRAY: ArrayVec<u8, 1024> = ArrayVec::new_const();
+    /// ```
+    pub const fn new_const() -> ArrayVec<T, CAP> {
+        assert_capacity_limit_const!(CAP);
+        ArrayVec { xs: MakeMaybeUninit::ARRAY, len: 0 }
+    }
+
+    /// Return the number of elements in the `ArrayVec`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3]);
+    /// array.pop();
+    /// assert_eq!(array.len(), 2);
+    /// ```
+    #[inline(always)]
+    pub const fn len(&self) -> usize { self.len as usize }
+
+    /// Returns whether the `ArrayVec` is empty.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1]);
+    /// array.pop();
+    /// assert_eq!(array.is_empty(), true);
+    /// ```
+    #[inline]
+    pub const fn is_empty(&self) -> bool { self.len() == 0 }
+
+    /// Return the capacity of the `ArrayVec`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let array = ArrayVec::from([1, 2, 3]);
+    /// assert_eq!(array.capacity(), 3);
+    /// ```
+    #[inline(always)]
+    pub const fn capacity(&self) -> usize { CAP }
+
+    /// Return true if the `ArrayVec` is completely filled to its capacity, false otherwise.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 1>::new();
+    /// assert!(!array.is_full());
+    /// array.push(1);
+    /// assert!(array.is_full());
+    /// ```
+    pub const fn is_full(&self) -> bool { self.len() == self.capacity() }
+
+    /// Returns the capacity left in the `ArrayVec`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3]);
+    /// array.pop();
+    /// assert_eq!(array.remaining_capacity(), 1);
+    /// ```
+    pub const fn remaining_capacity(&self) -> usize {
+        self.capacity() - self.len()
+    }
+
+    /// Push `element` to the end of the vector.
+    ///
+    /// ***Panics*** if the vector is already full.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 2>::new();
+    ///
+    /// array.push(1);
+    /// array.push(2);
+    ///
+    /// assert_eq!(&array[..], &[1, 2]);
+    /// ```
+    pub fn push(&mut self, element: T) {
+        ArrayVecImpl::push(self, element)
+    }
+
+    /// Push `element` to the end of the vector.
+    ///
+    /// Return `Ok` if the push succeeds, or return an error if the vector
+    /// is already full.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 2>::new();
+    ///
+    /// let push1 = array.try_push(1);
+    /// let push2 = array.try_push(2);
+    ///
+    /// assert!(push1.is_ok());
+    /// assert!(push2.is_ok());
+    ///
+    /// assert_eq!(&array[..], &[1, 2]);
+    ///
+    /// let overflow = array.try_push(3);
+    ///
+    /// assert!(overflow.is_err());
+    /// ```
+    pub fn try_push(&mut self, element: T) -> Result<(), CapacityError<T>> {
+        ArrayVecImpl::try_push(self, element)
+    }
+
+    /// Push `element` to the end of the vector without checking the capacity.
+    ///
+    /// It is up to the caller to ensure the capacity of the vector is
+    /// sufficiently large.
+    ///
+    /// This method uses *debug assertions* to check that the arrayvec is not full.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 2>::new();
+    ///
+    /// if array.len() + 2 <= array.capacity() {
+    ///     unsafe {
+    ///         array.push_unchecked(1);
+    ///         array.push_unchecked(2);
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&array[..], &[1, 2]);
+    /// ```
+    pub unsafe fn push_unchecked(&mut self, element: T) {
+        ArrayVecImpl::push_unchecked(self, element)
+    }
+
+    /// Shortens the vector, keeping the first `len` elements and dropping
+    /// the rest.
+    ///
+    /// If `len` is greater than the vector’s current length this has no
+    /// effect.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3, 4, 5]);
+    /// array.truncate(3);
+    /// assert_eq!(&array[..], &[1, 2, 3]);
+    /// array.truncate(4);
+    /// assert_eq!(&array[..], &[1, 2, 3]);
+    /// ```
+    pub fn truncate(&mut self, new_len: usize) {
+        ArrayVecImpl::truncate(self, new_len)
+    }
+
+    /// Remove all elements in the vector.
+    pub fn clear(&mut self) {
+        ArrayVecImpl::clear(self)
+    }
+
+
+    /// Get pointer to where element at `index` would be
+    unsafe fn get_unchecked_ptr(&mut self, index: usize) -> *mut T {
+        self.as_mut_ptr().add(index)
+    }
+
+    /// Insert `element` at position `index`.
+    ///
+    /// Shift up all elements after `index`.
+    ///
+    /// It is an error if the index is greater than the length or if the
+    /// arrayvec is full.
+    ///
+    /// ***Panics*** if the array is full or the `index` is out of bounds. See
+    /// `try_insert` for fallible version.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 2>::new();
+    ///
+    /// array.insert(0, "x");
+    /// array.insert(0, "y");
+    /// assert_eq!(&array[..], &["y", "x"]);
+    ///
+    /// ```
+    pub fn insert(&mut self, index: usize, element: T) {
+        self.try_insert(index, element).unwrap()
+    }
+
+    /// Insert `element` at position `index`.
+    ///
+    /// Shift up all elements after `index`; the `index` must be less than
+    /// or equal to the length.
+    ///
+    /// Returns an error if vector is already at full capacity.
+    ///
+    /// ***Panics*** `index` is out of bounds.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 2>::new();
+    ///
+    /// assert!(array.try_insert(0, "x").is_ok());
+    /// assert!(array.try_insert(0, "y").is_ok());
+    /// assert!(array.try_insert(0, "z").is_err());
+    /// assert_eq!(&array[..], &["y", "x"]);
+    ///
+    /// ```
+    pub fn try_insert(&mut self, index: usize, element: T) -> Result<(), CapacityError<T>> {
+        if index > self.len() {
+            panic_oob!("try_insert", index, self.len())
+        }
+        if self.len() == self.capacity() {
+            return Err(CapacityError::new(element));
+        }
+        let len = self.len();
+
+        // follows is just like Vec<T>
+        unsafe { // infallible
+            // The spot to put the new value
+            {
+                let p: *mut _ = self.get_unchecked_ptr(index);
+                // Shift everything over to make space. (Duplicating the
+                // `index`th element into two consecutive places.)
+                ptr::copy(p, p.offset(1), len - index);
+                // Write it in, overwriting the first copy of the `index`th
+                // element.
+                ptr::write(p, element);
+            }
+            self.set_len(len + 1);
+        }
+        Ok(())
+    }
+
+    /// Remove the last element in the vector and return it.
+    ///
+    /// Return `Some(` *element* `)` if the vector is non-empty, else `None`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::<_, 2>::new();
+    ///
+    /// array.push(1);
+    ///
+    /// assert_eq!(array.pop(), Some(1));
+    /// assert_eq!(array.pop(), None);
+    /// ```
+    pub fn pop(&mut self) -> Option<T> {
+        ArrayVecImpl::pop(self)
+    }
+
+    /// Remove the element at `index` and swap the last element into its place.
+    ///
+    /// This operation is O(1).
+    ///
+    /// Return the *element* if the index is in bounds, else panic.
+    ///
+    /// ***Panics*** if the `index` is out of bounds.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3]);
+    ///
+    /// assert_eq!(array.swap_remove(0), 1);
+    /// assert_eq!(&array[..], &[3, 2]);
+    ///
+    /// assert_eq!(array.swap_remove(1), 2);
+    /// assert_eq!(&array[..], &[3]);
+    /// ```
+    pub fn swap_remove(&mut self, index: usize) -> T {
+        self.swap_pop(index)
+            .unwrap_or_else(|| {
+                panic_oob!("swap_remove", index, self.len())
+            })
+    }
+
+    /// Remove the element at `index` and swap the last element into its place.
+    ///
+    /// This is a checked version of `.swap_remove`.  
+    /// This operation is O(1).
+    ///
+    /// Return `Some(` *element* `)` if the index is in bounds, else `None`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3]);
+    ///
+    /// assert_eq!(array.swap_pop(0), Some(1));
+    /// assert_eq!(&array[..], &[3, 2]);
+    ///
+    /// assert_eq!(array.swap_pop(10), None);
+    /// ```
+    pub fn swap_pop(&mut self, index: usize) -> Option<T> {
+        let len = self.len();
+        if index >= len {
+            return None;
+        }
+        self.swap(index, len - 1);
+        self.pop()
+    }
+
+    /// Remove the element at `index` and shift down the following elements.
+    ///
+    /// The `index` must be strictly less than the length of the vector.
+    ///
+    /// ***Panics*** if the `index` is out of bounds.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3]);
+    ///
+    /// let removed_elt = array.remove(0);
+    /// assert_eq!(removed_elt, 1);
+    /// assert_eq!(&array[..], &[2, 3]);
+    /// ```
+    pub fn remove(&mut self, index: usize) -> T {
+        self.pop_at(index)
+            .unwrap_or_else(|| {
+                panic_oob!("remove", index, self.len())
+            })
+    }
+
+    /// Remove the element at `index` and shift down the following elements.
+    ///
+    /// This is a checked version of `.remove(index)`. Returns `None` if there
+    /// is no element at `index`. Otherwise, return the element inside `Some`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3]);
+    ///
+    /// assert!(array.pop_at(0).is_some());
+    /// assert_eq!(&array[..], &[2, 3]);
+    ///
+    /// assert!(array.pop_at(2).is_none());
+    /// assert!(array.pop_at(10).is_none());
+    /// ```
+    pub fn pop_at(&mut self, index: usize) -> Option<T> {
+        if index >= self.len() {
+            None
+        } else {
+            self.drain(index..index + 1).next()
+        }
+    }
+
+    /// Retains only the elements specified by the predicate.
+    ///
+    /// In other words, remove all elements `e` such that `f(&mut e)` returns false.
+    /// This method operates in place and preserves the order of the retained
+    /// elements.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut array = ArrayVec::from([1, 2, 3, 4]);
+    /// array.retain(|x| *x & 1 != 0 );
+    /// assert_eq!(&array[..], &[1, 3]);
+    /// ```
+    pub fn retain<F>(&mut self, mut f: F)
+        where F: FnMut(&mut T) -> bool
+    {
+        // Check the implementation of
+        // https://doc.rust-lang.org/std/vec/struct.Vec.html#method.retain
+        // for safety arguments (especially regarding panics in f and when
+        // dropping elements). Implementation closely mirrored here.
+
+        let original_len = self.len();
+        unsafe { self.set_len(0) };
+
+        struct BackshiftOnDrop<'a, T, const CAP: usize> {
+            v: &'a mut ArrayVec<T, CAP>,
+            processed_len: usize,
+            deleted_cnt: usize,
+            original_len: usize,
+        }
+
+        impl<T, const CAP: usize> Drop for BackshiftOnDrop<'_, T, CAP> {
+            fn drop(&mut self) {
+                if self.deleted_cnt > 0 {
+                    unsafe {
+                        ptr::copy(
+                            self.v.as_ptr().add(self.processed_len),
+                            self.v.as_mut_ptr().add(self.processed_len - self.deleted_cnt),
+                            self.original_len - self.processed_len
+                        );
+                    }
+                }
+                unsafe {
+                    self.v.set_len(self.original_len - self.deleted_cnt);
+                }
+            }
+        }
+
+        let mut g = BackshiftOnDrop { v: self, processed_len: 0, deleted_cnt: 0, original_len };
+
+        #[inline(always)]
+        fn process_one<F: FnMut(&mut T) -> bool, T, const CAP: usize, const DELETED: bool>(
+            f: &mut F,
+            g: &mut BackshiftOnDrop<'_, T, CAP>
+        ) -> bool {
+            let cur = unsafe { g.v.as_mut_ptr().add(g.processed_len) };
+            if !f(unsafe { &mut *cur }) {
+                g.processed_len += 1;
+                g.deleted_cnt += 1;
+                unsafe { ptr::drop_in_place(cur) };
+                return false;
+            }
+            if DELETED {
+                unsafe {
+                    let hole_slot = g.v.as_mut_ptr().add(g.processed_len - g.deleted_cnt);
+                    ptr::copy_nonoverlapping(cur, hole_slot, 1);
+                }
+            }
+            g.processed_len += 1;
+            true
+        }
+
+        // Stage 1: Nothing was deleted.
+        while g.processed_len != original_len {
+            if !process_one::<F, T, CAP, false>(&mut f, &mut g) {
+                break;
+            }
+        }
+
+        // Stage 2: Some elements were deleted.
+        while g.processed_len != original_len {
+            process_one::<F, T, CAP, true>(&mut f, &mut g);
+        }
+
+        drop(g);
+    }
+
+    /// Set the vector’s length without dropping or moving out elements
+    ///
+    /// This method is `unsafe` because it changes the notion of the
+    /// number of “valid” elements in the vector. Use with care.
+    ///
+    /// This method uses *debug assertions* to check that `length` is
+    /// not greater than the capacity.
+    pub unsafe fn set_len(&mut self, length: usize) {
+        // type invariant that capacity always fits in LenUint
+        debug_assert!(length <= self.capacity());
+        self.len = length as LenUint;
+    }
+
+    /// Copy all elements from the slice and append to the `ArrayVec`.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut vec: ArrayVec<usize, 10> = ArrayVec::new();
+    /// vec.push(1);
+    /// vec.try_extend_from_slice(&[2, 3]).unwrap();
+    /// assert_eq!(&vec[..], &[1, 2, 3]);
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// This method will return an error if the capacity left (see
+    /// [`remaining_capacity`]) is smaller then the length of the provided
+    /// slice.
+    ///
+    /// [`remaining_capacity`]: #method.remaining_capacity
+    pub fn try_extend_from_slice(&mut self, other: &[T]) -> Result<(), CapacityError>
+        where T: Copy,
+    {
+        if self.remaining_capacity() < other.len() {
+            return Err(CapacityError::new(()));
+        }
+
+        let self_len = self.len();
+        let other_len = other.len();
+
+        unsafe {
+            let dst = self.get_unchecked_ptr(self_len);
+            ptr::copy_nonoverlapping(other.as_ptr(), dst, other_len);
+            self.set_len(self_len + other_len);
+        }
+        Ok(())
+    }
+
+    /// Create a draining iterator that removes the specified range in the vector
+    /// and yields the removed items from start to end. The element range is
+    /// removed even if the iterator is not consumed until the end.
+    ///
+    /// Note: It is unspecified how many elements are removed from the vector,
+    /// if the `Drain` value is leaked.
+    ///
+    /// **Panics** if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the vector.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut v1 = ArrayVec::from([1, 2, 3]);
+    /// let v2: ArrayVec<_, 3> = v1.drain(0..2).collect();
+    /// assert_eq!(&v1[..], &[3]);
+    /// assert_eq!(&v2[..], &[1, 2]);
+    /// ```
+    pub fn drain<R>(&mut self, range: R) -> Drain<T, CAP>
+        where R: RangeBounds<usize>
+    {
+        // Memory safety
+        //
+        // When the Drain is first created, it shortens the length of
+        // the source vector to make sure no uninitialized or moved-from elements
+        // are accessible at all if the Drain's destructor never gets to run.
+        //
+        // Drain will ptr::read out the values to remove.
+        // When finished, remaining tail of the vec is copied back to cover
+        // the hole, and the vector length is restored to the new length.
+        //
+        let len = self.len();
+        let start = match range.start_bound() {
+            Bound::Unbounded => 0,
+            Bound::Included(&i) => i,
+            Bound::Excluded(&i) => i.saturating_add(1),
+        };
+        let end = match range.end_bound() {
+            Bound::Excluded(&j) => j,
+            Bound::Included(&j) => j.saturating_add(1),
+            Bound::Unbounded => len,
+        };
+        self.drain_range(start, end)
+    }
+
+    fn drain_range(&mut self, start: usize, end: usize) -> Drain<T, CAP>
+    {
+        let len = self.len();
+
+        // bounds check happens here (before length is changed!)
+        let range_slice: *const _ = &self[start..end];
+
+        // Calling `set_len` creates a fresh and thus unique mutable references, making all
+        // older aliases we created invalid. So we cannot call that function.
+        self.len = start as LenUint;
+
+        unsafe {
+            Drain {
+                tail_start: end,
+                tail_len: len - end,
+                iter: (*range_slice).iter(),
+                vec: self as *mut _,
+            }
+        }
+    }
+
+    /// Return the inner fixed size array, if it is full to its capacity.
+    ///
+    /// Return an `Ok` value with the array if length equals capacity,
+    /// return an `Err` with self otherwise.
+    pub fn into_inner(self) -> Result<[T; CAP], Self> {
+        if self.len() < self.capacity() {
+            Err(self)
+        } else {
+            unsafe { Ok(self.into_inner_unchecked()) }
+        }
+    }
+
+    /// Return the inner fixed size array.
+    ///
+    /// Safety:
+    /// This operation is safe if and only if length equals capacity.
+    pub unsafe fn into_inner_unchecked(self) -> [T; CAP] {
+        debug_assert_eq!(self.len(), self.capacity());
+        let self_ = ManuallyDrop::new(self);
+        let array = ptr::read(self_.as_ptr() as *const [T; CAP]);
+        array
+    }
+
+    /// Returns the ArrayVec, replacing the original with a new empty ArrayVec.
+    ///
+    /// ```
+    /// use arrayvec::ArrayVec;
+    ///
+    /// let mut v = ArrayVec::from([0, 1, 2, 3]);
+    /// assert_eq!([0, 1, 2, 3], v.take().into_inner().unwrap());
+    /// assert!(v.is_empty());
+    /// ```
+    pub fn take(&mut self) -> Self  {
+        mem::replace(self, Self::new())
+    }
+
+    /// Return a slice containing all elements of the vector.
+    pub fn as_slice(&self) -> &[T] {
+        ArrayVecImpl::as_slice(self)
+    }
+
+    /// Return a mutable slice containing all elements of the vector.
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        ArrayVecImpl::as_mut_slice(self)
+    }
+
+    /// Return a raw pointer to the vector's buffer.
+    pub fn as_ptr(&self) -> *const T {
+        ArrayVecImpl::as_ptr(self)
+    }
+
+    /// Return a raw mutable pointer to the vector's buffer.
+    pub fn as_mut_ptr(&mut self) -> *mut T {
+        ArrayVecImpl::as_mut_ptr(self)
+    }
+}
+
+impl<T, const CAP: usize> ArrayVecImpl for ArrayVec<T, CAP> {
+    type Item = T;
+    const CAPACITY: usize = CAP;
+
+    fn len(&self) -> usize { self.len() }
+
+    unsafe fn set_len(&mut self, length: usize) {
+        debug_assert!(length <= CAP);
+        self.len = length as LenUint;
+    }
+
+    fn as_ptr(&self) -> *const Self::Item {
+        self.xs.as_ptr() as _
+    }
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Item {
+        self.xs.as_mut_ptr() as _
+    }
+}
+
+impl<T, const CAP: usize> Deref for ArrayVec<T, CAP> {
+    type Target = [T];
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        self.as_slice()
+    }
+}
+
+impl<T, const CAP: usize> DerefMut for ArrayVec<T, CAP> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.as_mut_slice()
+    }
+}
+
+
+/// Create an `ArrayVec` from an array.
+///
+/// ```
+/// use arrayvec::ArrayVec;
+///
+/// let mut array = ArrayVec::from([1, 2, 3]);
+/// assert_eq!(array.len(), 3);
+/// assert_eq!(array.capacity(), 3);
+/// ```
+impl<T, const CAP: usize> From<[T; CAP]> for ArrayVec<T, CAP> {
+    fn from(array: [T; CAP]) -> Self {
+        let array = ManuallyDrop::new(array);
+        let mut vec = <ArrayVec<T, CAP>>::new();
+        unsafe {
+            (&*array as *const [T; CAP] as *const [MaybeUninit<T>; CAP])
+                .copy_to_nonoverlapping(&mut vec.xs as *mut [MaybeUninit<T>; CAP], 1);
+            vec.set_len(CAP);
+        }
+        vec
+    }
+}
+
+
+/// Try to create an `ArrayVec` from a slice. This will return an error if the slice was too big to
+/// fit.
+///
+/// ```
+/// use arrayvec::ArrayVec;
+/// use std::convert::TryInto as _;
+///
+/// let array: ArrayVec<_, 4> = (&[1, 2, 3] as &[_]).try_into().unwrap();
+/// assert_eq!(array.len(), 3);
+/// assert_eq!(array.capacity(), 4);
+/// ```
+impl<T, const CAP: usize> std::convert::TryFrom<&[T]> for ArrayVec<T, CAP>
+    where T: Clone,
+{
+    type Error = CapacityError;
+
+    fn try_from(slice: &[T]) -> Result<Self, Self::Error> {
+        if Self::CAPACITY < slice.len() {
+            Err(CapacityError::new(()))
+        } else {
+            let mut array = Self::new();
+            array.extend_from_slice(slice);
+            Ok(array)
+        }
+    }
+}
+
+
+/// Iterate the `ArrayVec` with references to each element.
+///
+/// ```
+/// use arrayvec::ArrayVec;
+///
+/// let array = ArrayVec::from([1, 2, 3]);
+///
+/// for elt in &array {
+///     // ...
+/// }
+/// ```
+impl<'a, T: 'a, const CAP: usize> IntoIterator for &'a ArrayVec<T, CAP> {
+    type Item = &'a T;
+    type IntoIter = slice::Iter<'a, T>;
+    fn into_iter(self) -> Self::IntoIter { self.iter() }
+}
+
+/// Iterate the `ArrayVec` with mutable references to each element.
+///
+/// ```
+/// use arrayvec::ArrayVec;
+///
+/// let mut array = ArrayVec::from([1, 2, 3]);
+///
+/// for elt in &mut array {
+///     // ...
+/// }
+/// ```
+impl<'a, T: 'a, const CAP: usize> IntoIterator for &'a mut ArrayVec<T, CAP> {
+    type Item = &'a mut T;
+    type IntoIter = slice::IterMut<'a, T>;
+    fn into_iter(self) -> Self::IntoIter { self.iter_mut() }
+}
+
+/// Iterate the `ArrayVec` with each element by value.
+///
+/// The vector is consumed by this operation.
+///
+/// ```
+/// use arrayvec::ArrayVec;
+///
+/// for elt in ArrayVec::from([1, 2, 3]) {
+///     // ...
+/// }
+/// ```
+impl<T, const CAP: usize> IntoIterator for ArrayVec<T, CAP> {
+    type Item = T;
+    type IntoIter = IntoIter<T, CAP>;
+    fn into_iter(self) -> IntoIter<T, CAP> {
+        IntoIter { index: 0, v: self, }
+    }
+}
+
+
+/// By-value iterator for `ArrayVec`.
+pub struct IntoIter<T, const CAP: usize> {
+    index: usize,
+    v: ArrayVec<T, CAP>,
+}
+
+impl<T, const CAP: usize> Iterator for IntoIter<T, CAP> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.index == self.v.len() {
+            None
+        } else {
+            unsafe {
+                let index = self.index;
+                self.index = index + 1;
+                Some(ptr::read(self.v.get_unchecked_ptr(index)))
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.v.len() - self.index;
+        (len, Some(len))
+    }
+}
+
+impl<T, const CAP: usize> DoubleEndedIterator for IntoIter<T, CAP> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.index == self.v.len() {
+            None
+        } else {
+            unsafe {
+                let new_len = self.v.len() - 1;
+                self.v.set_len(new_len);
+                Some(ptr::read(self.v.get_unchecked_ptr(new_len)))
+            }
+        }
+    }
+}
+
+impl<T, const CAP: usize> ExactSizeIterator for IntoIter<T, CAP> { }
+
+impl<T, const CAP: usize> Drop for IntoIter<T, CAP> {
+    fn drop(&mut self) {
+        // panic safety: Set length to 0 before dropping elements.
+        let index = self.index;
+        let len = self.v.len();
+        unsafe {
+            self.v.set_len(0);
+            let elements = slice::from_raw_parts_mut(
+                self.v.get_unchecked_ptr(index),
+                len - index);
+            ptr::drop_in_place(elements);
+        }
+    }
+}
+
+impl<T, const CAP: usize> Clone for IntoIter<T, CAP>
+where T: Clone,
+{
+    fn clone(&self) -> IntoIter<T, CAP> {
+        let mut v = ArrayVec::new();
+        v.extend_from_slice(&self.v[self.index..]);
+        v.into_iter()
+    }
+}
+
+impl<T, const CAP: usize> fmt::Debug for IntoIter<T, CAP>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list()
+            .entries(&self.v[self.index..])
+            .finish()
+    }
+}
+
+/// A draining iterator for `ArrayVec`.
+pub struct Drain<'a, T: 'a, const CAP: usize> {
+    /// Index of tail to preserve
+    tail_start: usize,
+    /// Length of tail
+    tail_len: usize,
+    /// Current remaining range to remove
+    iter: slice::Iter<'a, T>,
+    vec: *mut ArrayVec<T, CAP>,
+}
+
+unsafe impl<'a, T: Sync, const CAP: usize> Sync for Drain<'a, T, CAP> {}
+unsafe impl<'a, T: Send, const CAP: usize> Send for Drain<'a, T, CAP> {}
+
+impl<'a, T: 'a, const CAP: usize> Iterator for Drain<'a, T, CAP> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next().map(|elt|
+            unsafe {
+                ptr::read(elt as *const _)
+            }
+        )
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<'a, T: 'a, const CAP: usize> DoubleEndedIterator for Drain<'a, T, CAP>
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(|elt|
+            unsafe {
+                ptr::read(elt as *const _)
+            }
+        )
+    }
+}
+
+impl<'a, T: 'a, const CAP: usize> ExactSizeIterator for Drain<'a, T, CAP> {}
+
+impl<'a, T: 'a, const CAP: usize> Drop for Drain<'a, T, CAP> {
+    fn drop(&mut self) {
+        // len is currently 0 so panicking while dropping will not cause a double drop.
+
+        // exhaust self first
+        while let Some(_) = self.next() { }
+
+        if self.tail_len > 0 {
+            unsafe {
+                let source_vec = &mut *self.vec;
+                // memmove back untouched tail, update to new length
+                let start = source_vec.len();
+                let tail = self.tail_start;
+                let src = source_vec.as_ptr().add(tail);
+                let dst = source_vec.as_mut_ptr().add(start);
+                ptr::copy(src, dst, self.tail_len);
+                source_vec.set_len(start + self.tail_len);
+            }
+        }
+    }
+}
+
+struct ScopeExitGuard<T, Data, F>
+    where F: FnMut(&Data, &mut T)
+{
+    value: T,
+    data: Data,
+    f: F,
+}
+
+impl<T, Data, F> Drop for ScopeExitGuard<T, Data, F>
+    where F: FnMut(&Data, &mut T)
+{
+    fn drop(&mut self) {
+        (self.f)(&self.data, &mut self.value)
+    }
+}
+
+
+
+/// Extend the `ArrayVec` with an iterator.
+/// 
+/// ***Panics*** if extending the vector exceeds its capacity.
+impl<T, const CAP: usize> Extend<T> for ArrayVec<T, CAP> {
+    /// Extend the `ArrayVec` with an iterator.
+    /// 
+    /// ***Panics*** if extending the vector exceeds its capacity.
+    fn extend<I: IntoIterator<Item=T>>(&mut self, iter: I) {
+        unsafe {
+            self.extend_from_iter::<_, true>(iter)
+        }
+    }
+}
+
+#[inline(never)]
+#[cold]
+fn extend_panic() {
+    panic!("ArrayVec: capacity exceeded in extend/from_iter");
+}
+
+impl<T, const CAP: usize> ArrayVec<T, CAP> {
+    /// Extend the arrayvec from the iterable.
+    ///
+    /// ## Safety
+    ///
+    /// Unsafe because if CHECK is false, the length of the input is not checked.
+    /// The caller must ensure the length of the input fits in the capacity.
+    pub(crate) unsafe fn extend_from_iter<I, const CHECK: bool>(&mut self, iterable: I)
+        where I: IntoIterator<Item = T>
+    {
+        let take = self.capacity() - self.len();
+        let len = self.len();
+        let mut ptr = raw_ptr_add(self.as_mut_ptr(), len);
+        let end_ptr = raw_ptr_add(ptr, take);
+        // Keep the length in a separate variable, write it back on scope
+        // exit. To help the compiler with alias analysis and stuff.
+        // We update the length to handle panic in the iteration of the
+        // user's iterator, without dropping any elements on the floor.
+        let mut guard = ScopeExitGuard {
+            value: &mut self.len,
+            data: len,
+            f: move |&len, self_len| {
+                **self_len = len as LenUint;
+            }
+        };
+        let mut iter = iterable.into_iter();
+        loop {
+            if let Some(elt) = iter.next() {
+                if ptr == end_ptr && CHECK { extend_panic(); }
+                debug_assert_ne!(ptr, end_ptr);
+                ptr.write(elt);
+                ptr = raw_ptr_add(ptr, 1);
+                guard.data += 1;
+            } else {
+                return; // success
+            }
+        }
+    }
+
+    /// Extend the ArrayVec with clones of elements from the slice;
+    /// the length of the slice must be <= the remaining capacity in the arrayvec.
+    pub(crate) fn extend_from_slice(&mut self, slice: &[T])
+        where T: Clone
+    {
+        let take = self.capacity() - self.len();
+        debug_assert!(slice.len() <= take);
+        unsafe {
+            let slice = if take < slice.len() { &slice[..take] } else { slice };
+            self.extend_from_iter::<_, false>(slice.iter().cloned());
+        }
+    }
+}
+
+/// Rawptr add but uses arithmetic distance for ZST
+unsafe fn raw_ptr_add<T>(ptr: *mut T, offset: usize) -> *mut T {
+    if mem::size_of::<T>() == 0 {
+        // Special case for ZST
+        (ptr as usize).wrapping_add(offset) as _
+    } else {
+        ptr.add(offset)
+    }
+}
+
+/// Create an `ArrayVec` from an iterator.
+/// 
+/// ***Panics*** if the number of elements in the iterator exceeds the arrayvec's capacity.
+impl<T, const CAP: usize> iter::FromIterator<T> for ArrayVec<T, CAP> {
+    /// Create an `ArrayVec` from an iterator.
+    /// 
+    /// ***Panics*** if the number of elements in the iterator exceeds the arrayvec's capacity.
+    fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> Self {
+        let mut array = ArrayVec::new();
+        array.extend(iter);
+        array
+    }
+}
+
+impl<T, const CAP: usize> Clone for ArrayVec<T, CAP>
+    where T: Clone
+{
+    fn clone(&self) -> Self {
+        self.iter().cloned().collect()
+    }
+
+    fn clone_from(&mut self, rhs: &Self) {
+        // recursive case for the common prefix
+        let prefix = cmp::min(self.len(), rhs.len());
+        self[..prefix].clone_from_slice(&rhs[..prefix]);
+
+        if prefix < self.len() {
+            // rhs was shorter
+            self.truncate(prefix);
+        } else {
+            let rhs_elems = &rhs[self.len()..];
+            self.extend_from_slice(rhs_elems);
+        }
+    }
+}
+
+impl<T, const CAP: usize> Hash for ArrayVec<T, CAP>
+    where T: Hash
+{
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        Hash::hash(&**self, state)
+    }
+}
+
+impl<T, const CAP: usize> PartialEq for ArrayVec<T, CAP>
+    where T: PartialEq
+{
+    fn eq(&self, other: &Self) -> bool {
+        **self == **other
+    }
+}
+
+impl<T, const CAP: usize> PartialEq<[T]> for ArrayVec<T, CAP>
+    where T: PartialEq
+{
+    fn eq(&self, other: &[T]) -> bool {
+        **self == *other
+    }
+}
+
+impl<T, const CAP: usize> Eq for ArrayVec<T, CAP> where T: Eq { }
+
+impl<T, const CAP: usize> Borrow<[T]> for ArrayVec<T, CAP> {
+    fn borrow(&self) -> &[T] { self }
+}
+
+impl<T, const CAP: usize> BorrowMut<[T]> for ArrayVec<T, CAP> {
+    fn borrow_mut(&mut self) -> &mut [T] { self }
+}
+
+impl<T, const CAP: usize> AsRef<[T]> for ArrayVec<T, CAP> {
+    fn as_ref(&self) -> &[T] { self }
+}
+
+impl<T, const CAP: usize> AsMut<[T]> for ArrayVec<T, CAP> {
+    fn as_mut(&mut self) -> &mut [T] { self }
+}
+
+impl<T, const CAP: usize> fmt::Debug for ArrayVec<T, CAP> where T: fmt::Debug {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { (**self).fmt(f) }
+}
+
+impl<T, const CAP: usize> Default for ArrayVec<T, CAP> {
+    /// Return an empty array
+    fn default() -> ArrayVec<T, CAP> {
+        ArrayVec::new()
+    }
+}
+
+impl<T, const CAP: usize> PartialOrd for ArrayVec<T, CAP> where T: PartialOrd {
+    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
+        (**self).partial_cmp(other)
+    }
+
+    fn lt(&self, other: &Self) -> bool {
+        (**self).lt(other)
+    }
+
+    fn le(&self, other: &Self) -> bool {
+        (**self).le(other)
+    }
+
+    fn ge(&self, other: &Self) -> bool {
+        (**self).ge(other)
+    }
+
+    fn gt(&self, other: &Self) -> bool {
+        (**self).gt(other)
+    }
+}
+
+impl<T, const CAP: usize> Ord for ArrayVec<T, CAP> where T: Ord {
+    fn cmp(&self, other: &Self) -> cmp::Ordering {
+        (**self).cmp(other)
+    }
+}
+
+#[cfg(feature="std")]
+/// `Write` appends written data to the end of the vector.
+///
+/// Requires `features="std"`.
+impl<const CAP: usize> io::Write for ArrayVec<u8, CAP> {
+    fn write(&mut self, data: &[u8]) -> io::Result<usize> {
+        let len = cmp::min(self.remaining_capacity(), data.len());
+        let _result = self.try_extend_from_slice(&data[..len]);
+        debug_assert!(_result.is_ok());
+        Ok(len)
+    }
+    fn flush(&mut self) -> io::Result<()> { Ok(()) }
+}
+
+#[cfg(feature="serde")]
+/// Requires crate feature `"serde"`
+impl<T: Serialize, const CAP: usize> Serialize for ArrayVec<T, CAP> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where S: Serializer
+    {
+        serializer.collect_seq(self)
+    }
+}
+
+#[cfg(feature="serde")]
+/// Requires crate feature `"serde"`
+impl<'de, T: Deserialize<'de>, const CAP: usize> Deserialize<'de> for ArrayVec<T, CAP> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where D: Deserializer<'de>
+    {
+        use serde::de::{Visitor, SeqAccess, Error};
+        use std::marker::PhantomData;
+
+        struct ArrayVecVisitor<'de, T: Deserialize<'de>, const CAP: usize>(PhantomData<(&'de (), [T; CAP])>);
+
+        impl<'de, T: Deserialize<'de>, const CAP: usize> Visitor<'de> for ArrayVecVisitor<'de, T, CAP> {
+            type Value = ArrayVec<T, CAP>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                write!(formatter, "an array with no more than {} items", CAP)
+            }
+
+            fn visit_seq<SA>(self, mut seq: SA) -> Result<Self::Value, SA::Error>
+                where SA: SeqAccess<'de>,
+            {
+                let mut values = ArrayVec::<T, CAP>::new();
+
+                while let Some(value) = seq.next_element()? {
+                    if let Err(_) = values.try_push(value) {
+                        return Err(SA::Error::invalid_length(CAP + 1, &self));
+                    }
+                }
+
+                Ok(values)
+            }
+        }
+
+        deserializer.deserialize_seq(ArrayVecVisitor::<T, CAP>(PhantomData))
+    }
+}
diff --git a/third_party/rust/arrayvec/src/arrayvec_impl.rs b/third_party/rust/arrayvec/src/arrayvec_impl.rs
new file mode 100644
index 0000000000..6c09834add
--- /dev/null
+++ b/third_party/rust/arrayvec/src/arrayvec_impl.rs
@@ -0,0 +1,86 @@
+use std::ptr;
+use std::slice;
+
+use crate::CapacityError;
+
+/// Implements basic arrayvec methods - based on a few required methods
+/// for length and element access.
+pub(crate) trait ArrayVecImpl {
+    type Item;
+    const CAPACITY: usize;
+
+    fn len(&self) -> usize;
+
+    unsafe fn set_len(&mut self, new_len: usize);
+
+    /// Return a slice containing all elements of the vector.
+    fn as_slice(&self) -> &[Self::Item] {
+        let len = self.len();
+        unsafe {
+            slice::from_raw_parts(self.as_ptr(), len)
+        }
+    }
+
+    /// Return a mutable slice containing all elements of the vector.
+    fn as_mut_slice(&mut self) -> &mut [Self::Item] {
+        let len = self.len();
+        unsafe {
+            std::slice::from_raw_parts_mut(self.as_mut_ptr(), len)
+        }
+    }
+
+    /// Return a raw pointer to the vector's buffer.
+    fn as_ptr(&self) -> *const Self::Item;
+
+    /// Return a raw mutable pointer to the vector's buffer.
+    fn as_mut_ptr(&mut self) -> *mut Self::Item;
+
+    fn push(&mut self, element: Self::Item) {
+        self.try_push(element).unwrap()
+    }
+
+    fn try_push(&mut self, element: Self::Item) -> Result<(), CapacityError<Self::Item>> {
+        if self.len() < Self::CAPACITY {
+            unsafe {
+                self.push_unchecked(element);
+            }
+            Ok(())
+        } else {
+            Err(CapacityError::new(element))
+        }
+    }
+
+    unsafe fn push_unchecked(&mut self, element: Self::Item) {
+        let len = self.len();
+        debug_assert!(len < Self::CAPACITY);
+        ptr::write(self.as_mut_ptr().add(len), element);
+        self.set_len(len + 1);
+    }
+
+    fn pop(&mut self) -> Option<Self::Item> {
+        if self.len() == 0 {
+            return None;
+        }
+        unsafe {
+            let new_len = self.len() - 1;
+            self.set_len(new_len);
+            Some(ptr::read(self.as_ptr().add(new_len)))
+        }
+    }
+
+    fn clear(&mut self) {
+        self.truncate(0)
+    }
+
+    fn truncate(&mut self, new_len: usize) {
+        unsafe {
+            let len = self.len();
+            if new_len < len {
+                self.set_len(new_len);
+                let tail = slice::from_raw_parts_mut(self.as_mut_ptr().add(new_len), len - new_len);
+                ptr::drop_in_place(tail);
+            }
+        }
+    }
+}
+
diff --git a/third_party/rust/arrayvec/src/char.rs b/third_party/rust/arrayvec/src/char.rs
new file mode 100644
index 0000000000..939b6b472a
--- /dev/null
+++ b/third_party/rust/arrayvec/src/char.rs
@@ -0,0 +1,92 @@
+// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// Original authors: alexchrichton, bluss
+
+// UTF-8 ranges and tags for encoding characters
+const TAG_CONT: u8    = 0b1000_0000;
+const TAG_TWO_B: u8   = 0b1100_0000;
+const TAG_THREE_B: u8 = 0b1110_0000;
+const TAG_FOUR_B: u8  = 0b1111_0000;
+const MAX_ONE_B: u32   =     0x80;
+const MAX_TWO_B: u32   =    0x800;
+const MAX_THREE_B: u32 =  0x10000;
+
+/// Placeholder
+pub struct EncodeUtf8Error;
+
+/// Encode a char into buf using UTF-8.
+///
+/// On success, return the byte length of the encoding (1, 2, 3 or 4).<br>
+/// On error, return `EncodeUtf8Error` if the buffer was too short for the char.
+///
+/// Safety: `ptr` must be writable for `len` bytes.
+#[inline]
+pub unsafe fn encode_utf8(ch: char, ptr: *mut u8, len: usize) -> Result<usize, EncodeUtf8Error>
+{
+    let code = ch as u32;
+    if code < MAX_ONE_B && len >= 1 {
+        ptr.add(0).write(code as u8);
+        return Ok(1);
+    } else if code < MAX_TWO_B && len >= 2 {
+        ptr.add(0).write((code >> 6 & 0x1F) as u8 | TAG_TWO_B);
+        ptr.add(1).write((code & 0x3F) as u8 | TAG_CONT);
+        return Ok(2);
+    } else if code < MAX_THREE_B && len >= 3 {
+        ptr.add(0).write((code >> 12 & 0x0F) as u8 | TAG_THREE_B);
+        ptr.add(1).write((code >>  6 & 0x3F) as u8 | TAG_CONT);
+        ptr.add(2).write((code & 0x3F) as u8 | TAG_CONT);
+        return Ok(3);
+    } else if len >= 4 {
+        ptr.add(0).write((code >> 18 & 0x07) as u8 | TAG_FOUR_B);
+        ptr.add(1).write((code >> 12 & 0x3F) as u8 | TAG_CONT);
+        ptr.add(2).write((code >>  6 & 0x3F) as u8 | TAG_CONT);
+        ptr.add(3).write((code & 0x3F) as u8 | TAG_CONT);
+        return Ok(4);
+    };
+    Err(EncodeUtf8Error)
+}
+
+
+#[test]
+#[cfg_attr(miri, ignore)] // Miri is too slow
+fn test_encode_utf8() {
+    // Test that all codepoints are encoded correctly
+    let mut data = [0u8; 16];
+    for codepoint in 0..=(std::char::MAX as u32) {
+        if let Some(ch) = std::char::from_u32(codepoint) {
+            for elt in &mut data { *elt = 0; }
+            let ptr = data.as_mut_ptr();
+            let len = data.len();
+            unsafe {
+                let res = encode_utf8(ch, ptr, len).ok().unwrap();
+                assert_eq!(res, ch.len_utf8());
+            }
+            let string = std::str::from_utf8(&data).unwrap();
+            assert_eq!(string.chars().next(), Some(ch));
+        }
+    }
+}
+
+#[test]
+fn test_encode_utf8_oob() {
+    // test that we report oob if the buffer is too short
+    let mut data = [0u8; 16];
+    let chars = ['a', 'α', '�', '𐍈'];
+    for (len, &ch) in (1..=4).zip(&chars) {
+        assert_eq!(len, ch.len_utf8(), "Len of ch={}", ch);
+        let ptr = data.as_mut_ptr();
+        unsafe {
+            assert!(matches::matches!(encode_utf8(ch, ptr, len - 1), Err(_)));
+            assert!(matches::matches!(encode_utf8(ch, ptr, len), Ok(_)));
+        }
+    }
+}
+
diff --git a/third_party/rust/arrayvec/src/errors.rs b/third_party/rust/arrayvec/src/errors.rs
new file mode 100644
index 0000000000..7ca3ebc4dc
--- /dev/null
+++ b/third_party/rust/arrayvec/src/errors.rs
@@ -0,0 +1,49 @@
+use std::fmt;
+#[cfg(feature="std")]
+use std::any::Any;
+#[cfg(feature="std")]
+use std::error::Error;
+
+/// Error value indicating insufficient capacity
+#[derive(Clone, Copy, Eq, Ord, PartialEq, PartialOrd)]
+pub struct CapacityError<T = ()> {
+    element: T,
+}
+
+impl<T> CapacityError<T> {
+    /// Create a new `CapacityError` from `element`.
+    pub const fn new(element: T) -> CapacityError<T> {
+        CapacityError {
+            element: element,
+        }
+    }
+
+    /// Extract the overflowing element
+    pub fn element(self) -> T {
+        self.element
+    }
+
+    /// Convert into a `CapacityError` that does not carry an element.
+    pub fn simplify(self) -> CapacityError {
+        CapacityError { element: () }
+    }
+}
+
+const CAPERROR: &'static str = "insufficient capacity";
+
+#[cfg(feature="std")]
+/// Requires `features="std"`.
+impl<T: Any> Error for CapacityError<T> {}
+
+impl<T> fmt::Display for CapacityError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", CAPERROR)
+    }
+}
+
+impl<T> fmt::Debug for CapacityError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}: {}", "CapacityError", CAPERROR)
+    }
+}
+
diff --git a/third_party/rust/arrayvec/src/lib.rs b/third_party/rust/arrayvec/src/lib.rs
new file mode 100644
index 0000000000..5dc0273a70
--- /dev/null
+++ b/third_party/rust/arrayvec/src/lib.rs
@@ -0,0 +1,59 @@
+//! **arrayvec** provides the types [`ArrayVec`] and [`ArrayString`]: 
+//! array-backed vector and string types, which store their contents inline.
+//!
+//! The arrayvec package has the following cargo features:
+//!
+//! - `std`
+//!   - Optional, enabled by default
+//!   - Use libstd; disable to use `no_std` instead.
+//!
+//! - `serde`
+//!   - Optional
+//!   - Enable serialization for ArrayVec and ArrayString using serde 1.x
+//!
+//! ## Rust Version
+//!
+//! This version of arrayvec requires Rust 1.51 or later.
+//!
+#![doc(html_root_url="https://docs.rs/arrayvec/0.7/")]
+#![cfg_attr(not(feature="std"), no_std)]
+
+#[cfg(feature="serde")]
+extern crate serde;
+
+#[cfg(not(feature="std"))]
+extern crate core as std;
+
+pub(crate) type LenUint = u32;
+
+macro_rules! assert_capacity_limit {
+    ($cap:expr) => {
+        if std::mem::size_of::<usize>() > std::mem::size_of::<LenUint>() {
+            if $cap > LenUint::MAX as usize {
+                panic!("ArrayVec: largest supported capacity is u32::MAX")
+            }
+        }
+    }
+}
+
+macro_rules! assert_capacity_limit_const {
+    ($cap:expr) => {
+        if std::mem::size_of::<usize>() > std::mem::size_of::<LenUint>() {
+            if $cap > LenUint::MAX as usize {
+                [/*ArrayVec: largest supported capacity is u32::MAX*/][$cap]
+            }
+        }
+    }
+}
+
+mod arrayvec_impl;
+mod arrayvec;
+mod array_string;
+mod char;
+mod errors;
+mod utils;
+
+pub use crate::array_string::ArrayString;
+pub use crate::errors::CapacityError;
+
+pub use crate::arrayvec::{ArrayVec, IntoIter, Drain};
diff --git a/third_party/rust/arrayvec/src/utils.rs b/third_party/rust/arrayvec/src/utils.rs
new file mode 100644
index 0000000000..b8e5ddb323
--- /dev/null
+++ b/third_party/rust/arrayvec/src/utils.rs
@@ -0,0 +1,11 @@
+use std::marker::PhantomData;
+use std::mem::MaybeUninit;
+
+pub(crate) struct MakeMaybeUninit<T, const N: usize>(PhantomData<fn() -> T>);
+
+impl<T, const N: usize> MakeMaybeUninit<T, N> {
+    pub(crate) const VALUE: MaybeUninit<T> = MaybeUninit::uninit();
+
+    pub(crate) const ARRAY: [MaybeUninit<T>; N] = [Self::VALUE; N];
+}
+