1 files changed, 32 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/src/utils.rs b/crates/ra_hir_ty/src/utils.rs
index 508ae9046..463fd65b4 100644
--- a/crates/ra_hir_ty/src/utils.rs
+++ b/crates/ra_hir_ty/src/utils.rs
@@ -62,6 +62,38 @@ pub(super) fn all_super_traits(db: &impl DefDatabase, trait_: TraitId) -> Vec<Tr
     result
 }
 
+/// Finds a path from a trait to one of its super traits. Returns an empty
+/// vector if there is no path.
+pub(super) fn find_super_trait_path(
+    db: &impl DefDatabase,
+    trait_: TraitId,
+    super_trait: TraitId,
+) -> Vec<TraitId> {
+    let mut result = Vec::with_capacity(2);
+    result.push(trait_);
+    return if go(db, super_trait, &mut result) { result } else { Vec::new() };
+
+    fn go(db: &impl DefDatabase, super_trait: TraitId, path: &mut Vec<TraitId>) -> bool {
+        let trait_ = *path.last().unwrap();
+        if trait_ == super_trait {
+            return true;
+        }
+
+        for tt in direct_super_traits(db, trait_) {
+            if path.contains(&tt) {
+                continue;
+            }
+            path.push(tt);
+            if go(db, super_trait, path) {
+                return true;
+            } else {
+                path.pop();
+            }
+        }
+        false
+    }
+}
+
 pub(super) fn associated_type_by_name_including_super_traits(
     db: &impl DefDatabase,
     trait_: TraitId,