1 files changed, 58 insertions, 0 deletions
diff --git a/third_party/rust/cranelift-entity-0.41.0/src/keys.rs b/third_party/rust/cranelift-entity-0.41.0/src/keys.rs
new file mode 100644
index 0000000000..bfbaa0cb90
--- /dev/null
+++ b/third_party/rust/cranelift-entity-0.41.0/src/keys.rs
@@ -0,0 +1,58 @@
+//! A double-ended iterator over entity references.
+//!
+//! When `core::iter::Step` is stabilized, `Keys` could be implemented as a wrapper around
+//! `core::ops::Range`, but for now, we implement it manually.
+
+use crate::EntityRef;
+use core::marker::PhantomData;
+
+/// Iterate over all keys in order.
+pub struct Keys<K: EntityRef> {
+    pos: usize,
+    rev_pos: usize,
+    unused: PhantomData<K>,
+}
+
+impl<K: EntityRef> Keys<K> {
+    /// Create a `Keys` iterator that visits `len` entities starting from 0.
+    pub fn with_len(len: usize) -> Self {
+        Self {
+            pos: 0,
+            rev_pos: len,
+            unused: PhantomData,
+        }
+    }
+}
+
+impl<K: EntityRef> Iterator for Keys<K> {
+    type Item = K;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.pos < self.rev_pos {
+            let k = K::new(self.pos);
+            self.pos += 1;
+            Some(k)
+        } else {
+            None
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let size = self.rev_pos - self.pos;
+        (size, Some(size))
+    }
+}
+
+impl<K: EntityRef> DoubleEndedIterator for Keys<K> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.rev_pos > self.pos {
+            let k = K::new(self.rev_pos - 1);
+            self.rev_pos -= 1;
+            Some(k)
+        } else {
+            None
+        }
+    }
+}
+
+impl<K: EntityRef> ExactSizeIterator for Keys<K> {}