1 files changed, 179 insertions, 0 deletions
diff --git a/third_party/rust/itertools/src/unique_impl.rs b/third_party/rust/itertools/src/unique_impl.rs
new file mode 100644
index 0000000000..4e81e78ec0
--- /dev/null
+++ b/third_party/rust/itertools/src/unique_impl.rs
@@ -0,0 +1,179 @@
+use std::collections::HashMap;
+use std::collections::hash_map::Entry;
+use std::hash::Hash;
+use std::fmt;
+use std::iter::FusedIterator;
+
+/// An iterator adapter to filter out duplicate elements.
+///
+/// See [`.unique_by()`](crate::Itertools::unique) for more information.
+#[derive(Clone)]
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct UniqueBy<I: Iterator, V, F> {
+    iter: I,
+    // Use a Hashmap for the Entry API in order to prevent hashing twice.
+    // This can maybe be replaced with a HashSet once `get_or_insert_with`
+    // or a proper Entry API for Hashset is stable and meets this msrv
+    used: HashMap<V, ()>,
+    f: F,
+}
+
+impl<I, V, F> fmt::Debug for UniqueBy<I, V, F>
+    where I: Iterator + fmt::Debug,
+          V: fmt::Debug + Hash + Eq,
+{
+    debug_fmt_fields!(UniqueBy, iter, used);
+}
+
+/// Create a new `UniqueBy` iterator.
+pub fn unique_by<I, V, F>(iter: I, f: F) -> UniqueBy<I, V, F>
+    where V: Eq + Hash,
+          F: FnMut(&I::Item) -> V,
+          I: Iterator,
+{
+    UniqueBy {
+        iter,
+        used: HashMap::new(),
+        f,
+    }
+}
+
+// count the number of new unique keys in iterable (`used` is the set already seen)
+fn count_new_keys<I, K>(mut used: HashMap<K, ()>, iterable: I) -> usize
+    where I: IntoIterator<Item=K>,
+          K: Hash + Eq,
+{
+    let iter = iterable.into_iter();
+    let current_used = used.len();
+    used.extend(iter.map(|key| (key, ())));
+    used.len() - current_used
+}
+
+impl<I, V, F> Iterator for UniqueBy<I, V, F>
+    where I: Iterator,
+          V: Eq + Hash,
+          F: FnMut(&I::Item) -> V
+{
+    type Item = I::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(v) = self.iter.next() {
+            let key = (self.f)(&v);
+            if self.used.insert(key, ()).is_none() {
+                return Some(v);
+            }
+        }
+        None
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (low, hi) = self.iter.size_hint();
+        ((low > 0 && self.used.is_empty()) as usize, hi)
+    }
+
+    fn count(self) -> usize {
+        let mut key_f = self.f;
+        count_new_keys(self.used, self.iter.map(move |elt| key_f(&elt)))
+    }
+}
+
+impl<I, V, F> DoubleEndedIterator for UniqueBy<I, V, F>
+    where I: DoubleEndedIterator,
+          V: Eq + Hash,
+          F: FnMut(&I::Item) -> V
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        while let Some(v) = self.iter.next_back() {
+            let key = (self.f)(&v);
+            if self.used.insert(key, ()).is_none() {
+                return Some(v);
+            }
+        }
+        None
+    }
+}
+
+impl<I, V, F> FusedIterator for UniqueBy<I, V, F>
+    where I: FusedIterator,
+          V: Eq + Hash,
+          F: FnMut(&I::Item) -> V
+{}
+
+impl<I> Iterator for Unique<I>
+    where I: Iterator,
+          I::Item: Eq + Hash + Clone
+{
+    type Item = I::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some(v) = self.iter.iter.next() {
+            if let Entry::Vacant(entry) = self.iter.used.entry(v) {
+                let elt = entry.key().clone();
+                entry.insert(());
+                return Some(elt);
+            }
+        }
+        None
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (low, hi) = self.iter.iter.size_hint();
+        ((low > 0 && self.iter.used.is_empty()) as usize, hi)
+    }
+
+    fn count(self) -> usize {
+        count_new_keys(self.iter.used, self.iter.iter)
+    }
+}
+
+impl<I> DoubleEndedIterator for Unique<I>
+    where I: DoubleEndedIterator,
+          I::Item: Eq + Hash + Clone
+{
+    fn next_back(&mut self) -> Option<Self::Item> {
+        while let Some(v) = self.iter.iter.next_back() {
+            if let Entry::Vacant(entry) = self.iter.used.entry(v) {
+                let elt = entry.key().clone();
+                entry.insert(());
+                return Some(elt);
+            }
+        }
+        None
+    }
+}
+
+impl<I> FusedIterator for Unique<I>
+    where I: FusedIterator,
+          I::Item: Eq + Hash + Clone
+{}
+
+/// An iterator adapter to filter out duplicate elements.
+///
+/// See [`.unique()`](crate::Itertools::unique) for more information.
+#[derive(Clone)]
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct Unique<I: Iterator> {
+    iter: UniqueBy<I, I::Item, ()>,
+}
+
+impl<I> fmt::Debug for Unique<I>
+    where I: Iterator + fmt::Debug,
+          I::Item: Hash + Eq + fmt::Debug,
+{
+    debug_fmt_fields!(Unique, iter);
+}
+
+pub fn unique<I>(iter: I) -> Unique<I>
+    where I: Iterator,
+          I::Item: Eq + Hash,
+{
+    Unique {
+        iter: UniqueBy {
+            iter,
+            used: HashMap::new(),
+            f: (),
+        }
+    }
+}