1 files changed, 87 insertions, 0 deletions
diff --git a/third_party/rust/itertools-0.8.0/src/merge_join.rs b/third_party/rust/itertools-0.8.0/src/merge_join.rs
new file mode 100644
index 0000000000..5f9a0f4013
--- /dev/null
+++ b/third_party/rust/itertools-0.8.0/src/merge_join.rs
@@ -0,0 +1,87 @@
+use std::cmp::Ordering;
+use std::iter::Fuse;
+use std::fmt;
+
+use super::adaptors::{PutBack, put_back};
+use either_or_both::EitherOrBoth;
+
+/// Return an iterator adaptor that merge-joins items from the two base iterators in ascending order.
+///
+/// See [`.merge_join_by()`](trait.Itertools.html#method.merge_join_by) for more information.
+pub fn merge_join_by<I, J, F>(left: I, right: J, cmp_fn: F)
+    -> MergeJoinBy<I::IntoIter, J::IntoIter, F>
+    where I: IntoIterator,
+          J: IntoIterator,
+          F: FnMut(&I::Item, &J::Item) -> Ordering
+{
+    MergeJoinBy {
+        left: put_back(left.into_iter().fuse()),
+        right: put_back(right.into_iter().fuse()),
+        cmp_fn: cmp_fn
+    }
+}
+
+/// An iterator adaptor that merge-joins items from the two base iterators in ascending order.
+///
+/// See [`.merge_join_by()`](../trait.Itertools.html#method.merge_join_by) for more information.
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct MergeJoinBy<I: Iterator, J: Iterator, F> {
+    left: PutBack<Fuse<I>>,
+    right: PutBack<Fuse<J>>,
+    cmp_fn: F
+}
+
+impl<I, J, F> fmt::Debug for MergeJoinBy<I, J, F>
+    where I: Iterator + fmt::Debug,
+          I::Item: fmt::Debug,
+          J: Iterator + fmt::Debug,
+          J::Item: fmt::Debug,
+{
+    debug_fmt_fields!(MergeJoinBy, left, right);
+}
+
+impl<I, J, F> Iterator for MergeJoinBy<I, J, F>
+    where I: Iterator,
+          J: Iterator,
+          F: FnMut(&I::Item, &J::Item) -> Ordering
+{
+    type Item = EitherOrBoth<I::Item, J::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match (self.left.next(), self.right.next()) {
+            (None, None) => None,
+            (Some(left), None) =>
+                Some(EitherOrBoth::Left(left)),
+            (None, Some(right)) =>
+                Some(EitherOrBoth::Right(right)),
+            (Some(left), Some(right)) => {
+                match (self.cmp_fn)(&left, &right) {
+                    Ordering::Equal =>
+                        Some(EitherOrBoth::Both(left, right)),
+                    Ordering::Less => {
+                        self.right.put_back(right);
+                        Some(EitherOrBoth::Left(left))
+                    },
+                    Ordering::Greater => {
+                        self.left.put_back(left);
+                        Some(EitherOrBoth::Right(right))
+                    }
+                }
+            }
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (a_lower, a_upper) = self.left.size_hint();
+        let (b_lower, b_upper) = self.right.size_hint();
+
+        let lower = ::std::cmp::max(a_lower, b_lower);
+
+        let upper = match (a_upper, b_upper) {
+            (Some(x), Some(y)) => Some(x + y),
+            _ => None,
+        };
+
+        (lower, upper)
+    }
+}