1 files changed, 70 insertions, 0 deletions
diff --git a/compiler/rustc_data_structures/src/vec_linked_list.rs b/compiler/rustc_data_structures/src/vec_linked_list.rs
new file mode 100644
index 000000000..ce60d40b2
--- /dev/null
+++ b/compiler/rustc_data_structures/src/vec_linked_list.rs
@@ -0,0 +1,70 @@
+use rustc_index::vec::{Idx, IndexVec};
+
+pub fn iter<Ls>(
+    first: Option<Ls::LinkIndex>,
+    links: &Ls,
+) -> impl Iterator<Item = Ls::LinkIndex> + '_
+where
+    Ls: Links,
+{
+    VecLinkedListIterator { links, current: first }
+}
+
+pub struct VecLinkedListIterator<Ls>
+where
+    Ls: Links,
+{
+    links: Ls,
+    current: Option<Ls::LinkIndex>,
+}
+
+impl<Ls> Iterator for VecLinkedListIterator<Ls>
+where
+    Ls: Links,
+{
+    type Item = Ls::LinkIndex;
+
+    fn next(&mut self) -> Option<Ls::LinkIndex> {
+        if let Some(c) = self.current {
+            self.current = <Ls as Links>::next(&self.links, c);
+            Some(c)
+        } else {
+            None
+        }
+    }
+}
+
+pub trait Links {
+    type LinkIndex: Copy;
+
+    fn next(links: &Self, index: Self::LinkIndex) -> Option<Self::LinkIndex>;
+}
+
+impl<Ls> Links for &Ls
+where
+    Ls: Links,
+{
+    type LinkIndex = Ls::LinkIndex;
+
+    fn next(links: &Self, index: Ls::LinkIndex) -> Option<Ls::LinkIndex> {
+        <Ls as Links>::next(links, index)
+    }
+}
+
+pub trait LinkElem {
+    type LinkIndex: Copy;
+
+    fn next(elem: &Self) -> Option<Self::LinkIndex>;
+}
+
+impl<L, E> Links for IndexVec<L, E>
+where
+    E: LinkElem<LinkIndex = L>,
+    L: Idx,
+{
+    type LinkIndex = L;
+
+    fn next(links: &Self, index: L) -> Option<L> {
+        <E as LinkElem>::next(&links[index])
+    }
+}