Adding upstream version 86.0.1.upstream/86.0.1upstream

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

8 files changed, 1014 insertions, 0 deletions

diff --git a/third_party/rust/thunderdome/src/arena.rs b/third_party/rust/thunderdome/src/arena.rs
new file mode 100644
index 0000000000..7125266071
--- /dev/null
+++ b/third_party/rust/thunderdome/src/arena.rs
@@ -0,0 +1,478 @@
+use std::convert::TryInto;
+use std::mem::replace;
+use std::ops;
+
+use crate::drain::Drain;
+use crate::free_pointer::FreePointer;
+use crate::generation::Generation;
+use crate::into_iter::IntoIter;
+use crate::iter::Iter;
+use crate::iter_mut::IterMut;
+
+/// Container that can have elements inserted into it and removed from it.
+///
+/// Indices use the [`Index`][Index] type, created by inserting values with
+/// [`Arena::insert`][Arena::insert].
+#[derive(Debug, Clone)]
+pub struct Arena<T> {
+    storage: Vec<Entry<T>>,
+    len: u32,
+    first_free: Option<FreePointer>,
+}
+
+/// Index type for [`Arena`][Arena] that has a generation attached to it.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct Index {
+    pub(crate) slot: u32,
+    pub(crate) generation: Generation,
+}
+
+impl Index {
+    /// Convert this `Index` to an equivalent `u64` representation. Mostly
+    /// useful for passing to code outside of Rust.
+    #[allow(clippy::integer_arithmetic)]
+    pub fn to_bits(self) -> u64 {
+        // This is safe because a `u32` bit-shifted by 32 will still fit in a `u64`.
+        ((self.generation.to_u32() as u64) << 32) | (self.slot as u64)
+    }
+
+    /// Convert back from a value generated with `Index::to_bits`. Don't call
+    /// this with arbitrary inputs; you'll almost certainly just get invalid
+    /// and/or malformed indices.
+    ///
+    /// If fed an index which was not generated by thunderdome or even just run
+    /// `Index::from_bits(0)`, this function may panic!
+    #[allow(clippy::integer_arithmetic)]
+    pub fn from_bits(bits: u64) -> Self {
+        // By bit-shifting right by 32, we're undoing the left-shift in `to_bits`
+        // thus this is okay by the same rationale.
+        let generation = Generation::from_u32((bits >> 32) as u32);
+        let slot = bits as u32;
+
+        Self { generation, slot }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub(crate) enum Entry<T> {
+    Occupied(OccupiedEntry<T>),
+    Empty(EmptyEntry),
+}
+
+impl<T> Entry<T> {
+    /// Consume the entry, and if it's occupied, return the value.
+    fn into_value(self) -> Option<T> {
+        match self {
+            Entry::Occupied(occupied) => Some(occupied.value),
+            Entry::Empty(_) => None,
+        }
+    }
+
+    /// If the entry is empty, return a copy of the emptiness data.
+    fn get_empty(&self) -> Option<EmptyEntry> {
+        match self {
+            Entry::Empty(empty) => Some(*empty),
+            Entry::Occupied(_) => None,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct OccupiedEntry<T> {
+    pub(crate) generation: Generation,
+    pub(crate) value: T,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct EmptyEntry {
+    pub(crate) generation: Generation,
+    pub(crate) next_free: Option<FreePointer>,
+}
+
+impl<T> Arena<T> {
+    /// Construct an empty arena.
+    pub fn new() -> Self {
+        Self {
+            storage: Vec::new(),
+            len: 0,
+            first_free: None,
+        }
+    }
+
+    /// Construct an empty arena with space to hold exactly `capacity` elements
+    /// without reallocating.
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            storage: Vec::with_capacity(capacity),
+            len: 0,
+            first_free: None,
+        }
+    }
+
+    /// Return the number of elements contained in the arena.
+    pub fn len(&self) -> usize {
+        self.len as usize
+    }
+
+    /// Return the number of elements the arena can hold without allocating,
+    /// including the elements currently in the arena.
+    pub fn capacity(&self) -> usize {
+        self.storage.capacity()
+    }
+
+    /// Returns whether the arena is empty.
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
+    /// Insert a new value into the arena, returning an index that can be used
+    /// to later retrieve the value.
+    pub fn insert(&mut self, value: T) -> Index {
+        // This value will definitely be inserted, so we can update length now.
+        self.len = self
+            .len
+            .checked_add(1)
+            .unwrap_or_else(|| panic!("Cannot insert more than u32::MAX elements into Arena"));
+
+        // If there was a previously free entry, we can re-use its slot as long
+        // as we increment its generation.
+        if let Some(free_pointer) = self.first_free {
+            let slot = free_pointer.slot();
+            let entry = self.storage.get_mut(slot as usize).unwrap_or_else(|| {
+                unreachable!("first_free pointed past the end of the arena's storage")
+            });
+
+            let empty = entry
+                .get_empty()
+                .unwrap_or_else(|| unreachable!("first_free pointed to an occupied entry"));
+
+            // If there is another empty entry after this one, we'll update the
+            // arena to point to it to use it on the next insertion.
+            self.first_free = empty.next_free;
+
+            // Overwrite the entry directly using our mutable reference instead
+            // of indexing into our storage again. This should avoid an
+            // additional bounds check.
+            let generation = empty.generation.next();
+            *entry = Entry::Occupied(OccupiedEntry { generation, value });
+
+            Index { slot, generation }
+        } else {
+            // There were no more empty entries left in our free list, so we'll
+            // create a new first-generation entry and push it into storage.
+
+            let generation = Generation::first();
+            let slot: u32 = self.storage.len().try_into().unwrap_or_else(|_| {
+                unreachable!("Arena storage exceeded what can be represented by a u32")
+            });
+
+            self.storage
+                .push(Entry::Occupied(OccupiedEntry { generation, value }));
+
+            Index { slot, generation }
+        }
+    }
+
+    /// Get an immutable reference to a value inside the arena by
+    /// [`Index`][Index], returning `None` if the index is not contained in the
+    /// arena.
+    pub fn get(&self, index: Index) -> Option<&T> {
+        match self.storage.get(index.slot as usize) {
+            Some(Entry::Occupied(occupied)) if occupied.generation == index.generation => {
+                Some(&occupied.value)
+            }
+            _ => None,
+        }
+    }
+
+    /// Get a mutable reference to a value inside the arena by [`Index`][Index],
+    /// returning `None` if the index is not contained in the arena.
+    pub fn get_mut(&mut self, index: Index) -> Option<&mut T> {
+        match self.storage.get_mut(index.slot as usize) {
+            Some(Entry::Occupied(occupied)) if occupied.generation == index.generation => {
+                Some(&mut occupied.value)
+            }
+            _ => None,
+        }
+    }
+
+    /// Remove the value contained at the given index from the arena, returning
+    /// it if it was present.
+    pub fn remove(&mut self, index: Index) -> Option<T> {
+        let entry = self.storage.get_mut(index.slot as usize)?;
+
+        match entry {
+            Entry::Occupied(occupied) if occupied.generation == index.generation => {
+                // We can replace an occupied entry with an empty entry with the
+                // same generation. On next insertion, this generation will
+                // increment.
+                let new_entry = Entry::Empty(EmptyEntry {
+                    generation: occupied.generation,
+                    next_free: self.first_free,
+                });
+
+                // Swap our new entry into our storage and take ownership of the
+                // old entry. We'll consume it for its value so we can give that
+                // back to our caller.
+                let old_entry = replace(entry, new_entry);
+                let value = old_entry.into_value().unwrap_or_else(|| unreachable!());
+
+                // The next time we insert, we can re-use the empty entry we
+                // just created. If another removal happens before then, that
+                // entry will be used before this one (FILO).
+                self.first_free = Some(FreePointer::from_slot(index.slot));
+
+                self.len = self.len.checked_sub(1).unwrap_or_else(|| unreachable!());
+
+                Some(value)
+            }
+            _ => None,
+        }
+    }
+
+    /// Invalidate the given index and return a new index to the same value. This
+    /// is roughly equivalent to `remove` followed by `insert`, but much faster.
+    /// If the old index is already invalid, this method returns `None`.
+    pub fn invalidate(&mut self, index: Index) -> Option<Index> {
+        let entry = self.storage.get_mut(index.slot as usize)?;
+
+        match entry {
+            Entry::Occupied(occupied) if occupied.generation == index.generation => {
+                occupied.generation = occupied.generation.next();
+
+                Some(Index {
+                    generation: occupied.generation,
+                    ..index
+                })
+            }
+            _ => None,
+        }
+    }
+
+    /// Clear the arena and drop all elements.
+    pub fn clear(&mut self) {
+        self.drain().for_each(drop);
+    }
+
+    /// Iterate over all of the indexes and values contained in the arena.
+    ///
+    /// Iteration order is not defined.
+    pub fn iter(&self) -> Iter<'_, T> {
+        Iter {
+            inner: self.storage.iter().enumerate(),
+            len: self.len,
+        }
+    }
+
+    /// Iterate over all of the indexes and values contained in the arena, with
+    /// mutable access to each value.
+    ///
+    /// Iteration order is not defined.
+    pub fn iter_mut(&mut self) -> IterMut<'_, T> {
+        IterMut {
+            inner: self.storage.iter_mut().enumerate(),
+            len: self.len,
+        }
+    }
+
+    /// Returns an iterator that removes each element from the arena.
+    ///
+    /// Iteration order is not defined.
+    ///
+    /// If the iterator is dropped before it is fully consumed, any uniterated
+    /// items will be dropped from the arena, and the arena will be empty.
+    /// The arena's capacity will not be changed.
+    pub fn drain(&mut self) -> Drain<'_, T> {
+        Drain {
+            arena: self,
+            slot: 0,
+        }
+    }
+}
+
+/// Methods exposed only within the crate.
+impl<T> Arena<T> {
+    /// This method is a lot like `remove`, but takes no generation. It's used
+    /// as part of `drain` and can likely be exposed as a public API eventually.
+    pub(crate) fn remove_entry_by_slot(&mut self, slot: u32) -> Option<(Index, T)> {
+        let entry = self.storage.get_mut(slot as usize)?;
+
+        match entry {
+            Entry::Occupied(occupied) => {
+                // Construct the index that would be used to access this entry.
+                let index = Index {
+                    generation: occupied.generation,
+                    slot,
+                };
+
+                // This occupied entry will be replaced with an empty one of the
+                // same generation. Generation will be incremented on the next
+                // insert.
+                let next_entry = Entry::Empty(EmptyEntry {
+                    generation: occupied.generation,
+                    next_free: self.first_free,
+                });
+
+                // Swap new entry into place and consume the old one.
+                let old_entry = replace(entry, next_entry);
+                let value = old_entry.into_value().unwrap_or_else(|| unreachable!());
+
+                // Set this entry as the next one that should be inserted into,
+                // should an insertion happen.
+                self.first_free = Some(FreePointer::from_slot(slot));
+
+                self.len = self.len.checked_sub(1).unwrap_or_else(|| unreachable!());
+
+                Some((index, value))
+            }
+            _ => None,
+        }
+    }
+}
+
+impl<T> Default for Arena<T> {
+    fn default() -> Self {
+        Arena::new()
+    }
+}
+
+impl<T> IntoIterator for Arena<T> {
+    type Item = (Index, T);
+    type IntoIter = IntoIter<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter {
+            arena: self,
+            slot: 0,
+        }
+    }
+}
+
+impl<T> ops::Index<Index> for Arena<T> {
+    type Output = T;
+
+    fn index(&self, index: Index) -> &Self::Output {
+        self.get(index)
+            .unwrap_or_else(|| panic!("No entry at index {:?}", index))
+    }
+}
+
+impl<T> ops::IndexMut<Index> for Arena<T> {
+    fn index_mut(&mut self, index: Index) -> &mut Self::Output {
+        self.get_mut(index)
+            .unwrap_or_else(|| panic!("No entry at index {:?}", index))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::{Arena, Index};
+
+    use std::mem::size_of;
+
+    #[test]
+    fn size_of_index() {
+        assert_eq!(size_of::<Index>(), 8);
+        assert_eq!(size_of::<Option<Index>>(), 8);
+    }
+
+    #[test]
+    fn new() {
+        let arena: Arena<u32> = Arena::new();
+        assert_eq!(arena.len(), 0);
+        assert_eq!(arena.capacity(), 0);
+    }
+
+    #[test]
+    fn with_capacity() {
+        let arena: Arena<u32> = Arena::with_capacity(8);
+        assert_eq!(arena.len(), 0);
+        assert_eq!(arena.capacity(), 8);
+    }
+
+    #[test]
+    fn insert_and_get() {
+        let mut arena = Arena::new();
+
+        let one = arena.insert(1);
+        assert_eq!(arena.len(), 1);
+        assert_eq!(arena.get(one), Some(&1));
+
+        let two = arena.insert(2);
+        assert_eq!(arena.len(), 2);
+        assert_eq!(arena.get(one), Some(&1));
+        assert_eq!(arena.get(two), Some(&2));
+    }
+
+    #[test]
+    fn insert_remove_get() {
+        let mut arena = Arena::new();
+        let one = arena.insert(1);
+
+        let two = arena.insert(2);
+        assert_eq!(arena.len(), 2);
+        assert_eq!(arena.remove(two), Some(2));
+
+        let three = arena.insert(3);
+        assert_eq!(arena.len(), 2);
+        assert_eq!(arena.get(one), Some(&1));
+        assert_eq!(arena.get(three), Some(&3));
+        assert_eq!(arena.get(two), None);
+    }
+
+    #[test]
+    fn get_mut() {
+        let mut arena = Arena::new();
+        let foo = arena.insert(5);
+
+        let handle = arena.get_mut(foo).unwrap();
+        *handle = 6;
+
+        assert_eq!(arena.get(foo), Some(&6));
+    }
+
+    #[test]
+    fn insert_remove_insert_capacity() {
+        let mut arena = Arena::with_capacity(2);
+        assert_eq!(arena.capacity(), 2);
+
+        let a = arena.insert("a");
+        let b = arena.insert("b");
+        assert_eq!(arena.len(), 2);
+        assert_eq!(arena.capacity(), 2);
+
+        arena.remove(a);
+        arena.remove(b);
+        assert_eq!(arena.len(), 0);
+        assert_eq!(arena.capacity(), 2);
+
+        let _a2 = arena.insert("a2");
+        let _b2 = arena.insert("b2");
+        assert_eq!(arena.len(), 2);
+        assert_eq!(arena.capacity(), 2);
+    }
+
+    #[test]
+    fn invalidate() {
+        let mut arena = Arena::new();
+
+        let a = arena.insert("a");
+        assert_eq!(arena.get(a), Some(&"a"));
+
+        let new_a = arena.invalidate(a).unwrap();
+        assert_eq!(arena.get(a), None);
+        assert_eq!(arena.get(new_a), Some(&"a"));
+    }
+
+    #[test]
+    fn index_bits_roundtrip() {
+        let index = Index::from_bits(0x1BADCAFE_DEADBEEF);
+        assert_eq!(index.to_bits(), 0x1BADCAFE_DEADBEEF);
+    }
+
+    #[test]
+    #[should_panic]
+    fn index_bits_panic_on_zero_generation() {
+        Index::from_bits(0x00000000_DEADBEEF);
+    }
+}
diff --git a/third_party/rust/thunderdome/src/drain.rs b/third_party/rust/thunderdome/src/drain.rs
new file mode 100644
index 0000000000..930c0962fa
--- /dev/null
+++ b/third_party/rust/thunderdome/src/drain.rs
@@ -0,0 +1,96 @@
+use std::iter::{ExactSizeIterator, FusedIterator};
+
+use crate::arena::{Arena, Index};
+
+/// See [`Arena::drain`][Arena::drain].
+pub struct Drain<'a, T> {
+    pub(crate) arena: &'a mut Arena<T>,
+    pub(crate) slot: u32,
+}
+
+impl<'a, T> Iterator for Drain<'a, T> {
+    type Item = (Index, T);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            // If there are no entries remaining in the arena, we should always
+            // return None. Using this check instead of comparing with the
+            // arena's size allows us to skip any trailing empty entries.
+            if self.arena.is_empty() {
+                return None;
+            }
+
+            // slot may overflow if the arena's underlying storage contains more
+            // than 2^32 elements, but its internal length value was not
+            // changed, as it overflowing would panic before reaching this code.
+            let slot = self.slot;
+            self.slot = self
+                .slot
+                .checked_add(1)
+                .unwrap_or_else(|| panic!("Overflowed u32 trying to drain Arena"));
+
+            // If this entry is occupied, this method will mark it as an empty.
+            // Otherwise, we'll continue looping until we've drained all
+            // occupied entries from the arena.
+            if let Some((index, value)) = self.arena.remove_entry_by_slot(slot) {
+                return Some((index, value));
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.arena.len(), Some(self.arena.len()))
+    }
+}
+
+impl<'a, T> FusedIterator for Drain<'a, T> {}
+impl<'a, T> ExactSizeIterator for Drain<'a, T> {}
+
+impl<'a, T> Drop for Drain<'a, T> {
+    // Continue iterating/dropping if there are any elements left.
+    fn drop(&mut self) {
+        self.for_each(drop);
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::Arena;
+
+    use std::collections::HashSet;
+
+    #[test]
+    fn drain() {
+        let mut arena = Arena::with_capacity(2);
+        let one = arena.insert(1);
+        let two = arena.insert(2);
+
+        let mut drained_pairs = HashSet::new();
+        {
+            let mut drain = arena.drain();
+            assert_eq!(drain.size_hint(), (2, Some(2)));
+
+            drained_pairs.insert(drain.next().unwrap());
+            assert_eq!(drain.size_hint(), (1, Some(1)));
+
+            // Do not fully drain so we can ensure everything is dropped when the
+            // `Drain` is dropped.
+            assert_eq!(drain.size_hint(), (1, Some(1)));
+        }
+
+        assert_eq!(arena.len(), 0);
+        assert_eq!(arena.capacity(), 2);
+        assert_eq!(drained_pairs.len(), 1);
+
+        // We should still be able to use the arena after this.
+        let one_prime = arena.insert(1);
+        let two_prime = arena.insert(2);
+
+        assert_eq!(arena.len(), 2);
+        assert_eq!(arena.capacity(), 2);
+        assert_eq!(arena.get(one_prime), Some(&1));
+        assert_eq!(arena.get(two_prime), Some(&2));
+        assert_eq!(arena.get(one), None);
+        assert_eq!(arena.get(two), None);
+    }
+}
diff --git a/third_party/rust/thunderdome/src/free_pointer.rs b/third_party/rust/thunderdome/src/free_pointer.rs
new file mode 100644
index 0000000000..e0d5f4ae8a
--- /dev/null
+++ b/third_party/rust/thunderdome/src/free_pointer.rs
@@ -0,0 +1,46 @@
+use std::num::NonZeroU32;

+

+/// Contains a reference to a free slot in an arena, encapsulating NonZeroU32

+/// to prevent off-by-one errors and leaking unsafety.

+///

+/// Uses NonZeroU32 to stay small when put inside an `Option`.

+#[derive(Debug, Clone, Copy)]

+#[repr(transparent)]

+pub(crate) struct FreePointer(NonZeroU32);

+

+impl FreePointer {

+    #[must_use]

+    pub(crate) fn from_slot(slot: u32) -> Self {

+        let value = slot

+            .checked_add(1)

+            .expect("u32 overflowed calculating free pointer from u32");

+

+        // This is safe because any u32 + 1 that didn't overflow must not be

+        // zero.

+        FreePointer(unsafe { NonZeroU32::new_unchecked(value) })

+    }

+

+    #[must_use]

+    #[allow(clippy::integer_arithmetic)]

+    pub(crate) fn slot(self) -> u32 {

+        // This will never underflow due to the field being guaranteed non-zero.

+        self.0.get() - 1

+    }

+}

+

+#[cfg(test)]

+mod test {

+    use super::FreePointer;

+

+    #[test]

+    fn from_slot() {

+        let ptr = FreePointer::from_slot(0);

+        assert_eq!(ptr.slot(), 0);

+    }

+

+    #[test]

+    #[should_panic(expected = "u32 overflowed calculating free pointer from u32")]

+    fn panic_on_overflow() {

+        let _ = FreePointer::from_slot(std::u32::MAX);

+    }

+}

diff --git a/third_party/rust/thunderdome/src/generation.rs b/third_party/rust/thunderdome/src/generation.rs
new file mode 100644
index 0000000000..e6982c383c
--- /dev/null
+++ b/third_party/rust/thunderdome/src/generation.rs
@@ -0,0 +1,61 @@
+use std::num::NonZeroU32;
+
+/// Tracks the generation of an entry in an arena. Encapsulates NonZeroU32 to
+/// reduce the number of redundant checks needed, as well as enforcing checked
+/// arithmetic on advancing a generation.
+///
+/// Uses NonZeroU32 to help `Index` stay the same size when put inside an
+/// `Option`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+#[repr(transparent)]
+pub(crate) struct Generation(NonZeroU32);
+
+impl Generation {
+    #[must_use]
+    pub(crate) fn first() -> Self {
+        // This is safe because 1 is not zero.
+        Generation(unsafe { NonZeroU32::new_unchecked(1) })
+    }
+
+    #[must_use]
+    pub(crate) fn next(self) -> Self {
+        let last_generation = self.0.get();
+        let next_generation = last_generation.checked_add(1).unwrap_or(1);
+
+        // This is safe because value that would overflow is instead made 1.
+        Generation(unsafe { NonZeroU32::new_unchecked(next_generation) })
+    }
+
+    pub(crate) fn to_u32(self) -> u32 {
+        self.0.get()
+    }
+
+    pub(crate) fn from_u32(gen: u32) -> Self {
+        Generation(NonZeroU32::new(gen).expect("generation IDs must be nonzero!"))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::Generation;
+
+    use std::num::NonZeroU32;
+
+    #[test]
+    fn first_and_next() {
+        let first = Generation::first();
+        assert_eq!(first.0.get(), 1);
+
+        let second = first.next();
+        assert_eq!(second.0.get(), 2);
+    }
+
+    #[test]
+    fn wrap_on_overflow() {
+        let max = Generation(NonZeroU32::new(std::u32::MAX).unwrap());
+        assert_eq!(max.0.get(), std::u32::MAX);
+
+        let next = max.next();
+        assert_eq!(next.0.get(), 1);
+    }
+}
diff --git a/third_party/rust/thunderdome/src/into_iter.rs b/third_party/rust/thunderdome/src/into_iter.rs
new file mode 100644
index 0000000000..e7dd0d9403
--- /dev/null
+++ b/third_party/rust/thunderdome/src/into_iter.rs
@@ -0,0 +1,79 @@
+use std::iter::{ExactSizeIterator, FusedIterator};

+

+use crate::arena::{Arena, Index};

+

+/// Iterator typed used when an Arena is turned [`IntoIterator`][IntoIterator].

+pub struct IntoIter<T> {

+    pub(crate) arena: Arena<T>,

+    pub(crate) slot: u32,

+}

+

+impl<T> Iterator for IntoIter<T> {

+    type Item = (Index, T);

+

+    fn next(&mut self) -> Option<Self::Item> {

+        loop {

+            // If there are no entries remaining in the arena, we should always

+            // return None. Using this check instead of comparing with the

+            // arena's size allows us to skip any trailing empty entries.

+            if self.arena.is_empty() {

+                return None;

+            }

+

+            // slot may overflow if the arena's underlying storage contains more

+            // than 2^32 elements, but its internal length value was not

+            // changed, as it overflowing would panic before reaching this code.

+            let slot = self.slot;

+            self.slot = self

+                .slot

+                .checked_add(1)

+                .unwrap_or_else(|| panic!("Overflowed u32 trying to into_iter Arena"));

+

+            // If this entry is occupied, this method will mark it as an empty.

+            // Otherwise, we'll continue looping until we've removed all

+            // occupied entries from the arena.

+            if let Some((index, value)) = self.arena.remove_entry_by_slot(slot) {

+                return Some((index, value));

+            }

+        }

+    }

+

+    fn size_hint(&self) -> (usize, Option<usize>) {

+        (self.arena.len(), Some(self.arena.len()))

+    }

+}

+

+impl<T> FusedIterator for IntoIter<T> {}

+impl<T> ExactSizeIterator for IntoIter<T> {}

+

+#[cfg(test)]

+mod test {

+    use crate::Arena;

+

+    use std::collections::HashSet;

+

+    #[test]

+    fn into_iter() {

+        let mut arena = Arena::with_capacity(2);

+        let one = arena.insert(1);

+        let two = arena.insert(2);

+

+        let mut pairs = HashSet::new();

+        let mut into_iter = arena.into_iter();

+        assert_eq!(into_iter.size_hint(), (2, Some(2)));

+

+        pairs.insert(into_iter.next().unwrap());

+        assert_eq!(into_iter.size_hint(), (1, Some(1)));

+

+        pairs.insert(into_iter.next().unwrap());

+        assert_eq!(into_iter.size_hint(), (0, Some(0)));

+

+        assert_eq!(into_iter.next(), None);

+        assert_eq!(into_iter.next(), None);

+        assert_eq!(into_iter.size_hint(), (0, Some(0)));

+

+        assert_eq!(pairs.len(), 2);

+        assert!(pairs.contains(&(one, 1)));

+        assert!(pairs.contains(&(two, 2)));

+    }

+}

diff --git a/third_party/rust/thunderdome/src/iter.rs b/third_party/rust/thunderdome/src/iter.rs
new file mode 100644
index 0000000000..0a2404cae7
--- /dev/null
+++ b/third_party/rust/thunderdome/src/iter.rs
@@ -0,0 +1,82 @@
+use std::convert::TryInto;

+use std::iter::{Enumerate, ExactSizeIterator, FusedIterator};

+use std::slice;

+

+use crate::arena::{Entry, Index};

+

+/// See [`Arena::iter`][Arena::iter].

+pub struct Iter<'a, T> {

+    pub(crate) len: u32,

+    pub(crate) inner: Enumerate<slice::Iter<'a, Entry<T>>>,

+}

+

+impl<'a, T> Iterator for Iter<'a, T> {

+    type Item = (Index, &'a T);

+

+    fn next(&mut self) -> Option<Self::Item> {

+        loop {

+            if self.len == 0 {

+                return None;

+            }

+

+            match self.inner.next()? {

+                (_, Entry::Empty(_)) => continue,

+                (slot, Entry::Occupied(occupied)) => {

+                    self.len = self

+                        .len

+                        .checked_sub(1)

+                        .unwrap_or_else(|| unreachable!("Underflowed u32 trying to iterate Arena"));

+

+                    let slot: u32 = slot

+                        .try_into()

+                        .unwrap_or_else(|_| unreachable!("Overflowed u32 trying to iterate Arena"));

+

+                    let index = Index {

+                        slot,

+                        generation: occupied.generation,

+                    };

+

+                    return Some((index, &occupied.value));

+                }

+            }

+        }

+    }

+

+    fn size_hint(&self) -> (usize, Option<usize>) {

+        (self.len as usize, Some(self.len as usize))

+    }

+}

+

+impl<'a, T> FusedIterator for Iter<'a, T> {}

+impl<'a, T> ExactSizeIterator for Iter<'a, T> {}

+

+#[cfg(test)]

+mod test {

+    use crate::Arena;

+

+    use std::collections::HashSet;

+

+    #[test]

+    fn iter() {

+        let mut arena = Arena::with_capacity(2);

+        let one = arena.insert(1);

+        let two = arena.insert(2);

+

+        let mut pairs = HashSet::new();

+        let mut iter = arena.iter();

+        assert_eq!(iter.size_hint(), (2, Some(2)));

+

+        pairs.insert(iter.next().unwrap());

+        assert_eq!(iter.size_hint(), (1, Some(1)));

+

+        pairs.insert(iter.next().unwrap());

+        assert_eq!(iter.size_hint(), (0, Some(0)));

+

+        assert_eq!(iter.next(), None);

+        assert_eq!(iter.next(), None);

+        assert_eq!(iter.size_hint(), (0, Some(0)));

+

+        assert!(pairs.contains(&(one, &1)));

+        assert!(pairs.contains(&(two, &2)));

+    }

+}

diff --git a/third_party/rust/thunderdome/src/iter_mut.rs b/third_party/rust/thunderdome/src/iter_mut.rs
new file mode 100644
index 0000000000..7ff71c12e3
--- /dev/null
+++ b/third_party/rust/thunderdome/src/iter_mut.rs
@@ -0,0 +1,82 @@
+use std::convert::TryInto;

+use std::iter::{Enumerate, ExactSizeIterator, FusedIterator};

+use std::slice;

+

+use crate::arena::{Entry, Index};

+

+/// See [`Arena::iter_mut`][Arena::iter_mut].

+pub struct IterMut<'a, T> {

+    pub(crate) len: u32,

+    pub(crate) inner: Enumerate<slice::IterMut<'a, Entry<T>>>,

+}

+

+impl<'a, T> Iterator for IterMut<'a, T> {

+    type Item = (Index, &'a T);

+

+    fn next(&mut self) -> Option<Self::Item> {

+        loop {

+            if self.len == 0 {

+                return None;

+            }

+

+            match self.inner.next()? {

+                (_, Entry::Empty(_)) => continue,

+                (slot, Entry::Occupied(occupied)) => {

+                    self.len = self

+                        .len

+                        .checked_sub(1)

+                        .unwrap_or_else(|| unreachable!("Underflowed u32 trying to iterate Arena"));

+

+                    let slot: u32 = slot

+                        .try_into()

+                        .unwrap_or_else(|_| unreachable!("Overflowed u32 trying to iterate Arena"));

+

+                    let index = Index {

+                        slot,

+                        generation: occupied.generation,

+                    };

+

+                    return Some((index, &mut occupied.value));

+                }

+            }

+        }

+    }

+

+    fn size_hint(&self) -> (usize, Option<usize>) {

+        (self.len as usize, Some(self.len as usize))

+    }

+}

+

+impl<'a, T> FusedIterator for IterMut<'a, T> {}

+impl<'a, T> ExactSizeIterator for IterMut<'a, T> {}

+

+#[cfg(test)]

+mod test {

+    use crate::Arena;

+

+    use std::collections::HashSet;

+

+    #[test]

+    fn iter_mut() {

+        let mut arena = Arena::with_capacity(2);

+        let one = arena.insert(1);

+        let two = arena.insert(2);

+

+        let mut pairs = HashSet::new();

+        let mut iter = arena.iter_mut();

+        assert_eq!(iter.size_hint(), (2, Some(2)));

+

+        pairs.insert(iter.next().unwrap());

+        assert_eq!(iter.size_hint(), (1, Some(1)));

+

+        pairs.insert(iter.next().unwrap());

+        assert_eq!(iter.size_hint(), (0, Some(0)));

+

+        assert_eq!(iter.next(), None);

+        assert_eq!(iter.next(), None);

+        assert_eq!(iter.size_hint(), (0, Some(0)));

+

+        assert!(pairs.contains(&(one, &1)));

+        assert!(pairs.contains(&(two, &2)));

+    }

+}

diff --git a/third_party/rust/thunderdome/src/lib.rs b/third_party/rust/thunderdome/src/lib.rs
new file mode 100644
index 0000000000..08bd29e07e
--- /dev/null
+++ b/third_party/rust/thunderdome/src/lib.rs
@@ -0,0 +1,90 @@
+/*!
+[![GitHub CI Status](https://github.com/LPGhatguy/thunderdome/workflows/CI/badge.svg)](https://github.com/LPGhatguy/thunderdome/actions)
+[![thunderdome on crates.io](https://img.shields.io/crates/v/thunderdome.svg)](https://crates.io/crates/thunderdome)
+[![thunderdome docs](https://img.shields.io/badge/docs-docs.rs-orange.svg)](https://docs.rs/thunderdome)
+
+Thunderdome is a ~gladitorial~ generational arena inspired by
+[generational-arena](https://crates.io/crates/generational-arena),
+[slotmap](https://crates.io/crates/slotmap), and
+[slab](https://crates.io/crates/slab). It provides constant time insertion,
+lookup, and removal via small (8 byte) keys returned from `Arena`.
+
+Thunderdome's key type, `Index`, is still 8 bytes when put inside of an
+`Option<T>` thanks to Rust's `NonZero*` types.
+
+## Basic Examples
+
+```rust
+# use thunderdome::{Arena, Index};
+let mut arena = Arena::new();
+
+let foo = arena.insert("Foo");
+let bar = arena.insert("Bar");
+
+assert_eq!(arena[foo], "Foo");
+assert_eq!(arena[bar], "Bar");
+
+arena[bar] = "Replaced";
+assert_eq!(arena[bar], "Replaced");
+
+let foo_value = arena.remove(foo);
+assert_eq!(foo_value, Some("Foo"));
+
+// The slot previously used by foo will be reused for baz
+let baz = arena.insert("Baz");
+assert_eq!(arena[baz], "Baz");
+
+// foo is no longer a valid key
+assert_eq!(arena.get(foo), None);
+```
+
+## Comparison With Similar Crates
+
+| Feature                      | Thunderdome | generational-arena | slotmap | slab |
+|------------------------------|-------------|--------------------|---------|------|
+| Generational Indices¹        | Yes         | Yes                | Yes     | No   |
+| `size_of::<Index>()`         | 8           | 16                 | 8       | 8    |
+| `size_of::<Option<Index>>()` | 8           | 24                 | 8       | 16   |
+| Max Elements                 | 2³²         | 2⁶⁴                | 2³²     | 2⁶⁴  |
+| Non-`Copy` Values            | Yes         | Yes                | Sorta²  | Yes  |
+| `no_std` Support             | No          | Yes                | No      | No   |
+| Serde Support                | No          | Yes                | Yes     | No   |
+
+* Sizes calculated on rustc `1.44.0-x86_64-pc-windows-msvc`
+* See [the Thunderdome comparison
+  Cargo.toml](https://github.com/LPGhatguy/thunderdome/blob/main/comparison/Cargo.toml)
+  for versions of each library tested.
+
+1. Generational indices help solve the [ABA
+   Problem](https://en.wikipedia.org/wiki/ABA_problem), which can cause dangling
+   keys to mistakenly access newly-inserted data.
+2. slotmap's `SlotMap` and `HopSlotMap` require values to be `Copy` on stable
+  Rust versions. slotmap's `DenseSlotMap` type supports non-`Copy` types on
+  stable, but has different performance trade-offs.
+
+## Minimum Supported Rust Version (MSRV)
+
+Thunderdome supports Rust 1.34.1 and newer. Until Thunderdome reaches 1.0,
+changes to the MSRV will require major version bumps. After 1.0, MSRV changes
+will only require minor version bumps, but will need significant justification.
+*/
+
+#![forbid(missing_docs)]
+// This crate is sensitive to integer overflow and wrapping behavior. As such,
+// we should usually use methods like `checked_add` and `checked_sub` instead
+// of the `Add` or `Sub` operators.
+#![deny(clippy::integer_arithmetic)]
+
+mod arena;
+mod drain;
+mod free_pointer;
+mod generation;
+mod into_iter;
+mod iter;
+mod iter_mut;
+
+pub use crate::arena::{Arena, Index};
+pub use crate::drain::Drain;
+pub use crate::into_iter::IntoIter;
+pub use crate::iter::Iter;
+pub use crate::iter_mut::IterMut;