diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index e39f06e687..d1a9d74111 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -400,6 +400,7 @@ impl SubstsBuilder {
 
     pub fn fill(mut self, filler: impl Iterator<Item = Ty>) -> Self {
         self.vec.extend(filler.take(self.remaining()));
+        assert_eq!(self.remaining(), 0);
         self
     }
 
diff --git a/crates/ra_hir/src/ty/infer/path.rs b/crates/ra_hir/src/ty/infer/path.rs
index 1946bf6084..59b7f7eb64 100644
--- a/crates/ra_hir/src/ty/infer/path.rs
+++ b/crates/ra_hir/src/ty/infer/path.rs
@@ -196,13 +196,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                     AssocItem::Const(c) => ValueNs::Const(c),
                     AssocItem::TypeAlias(_) => unreachable!(),
                 };
-                match item.container(self.db) {
-                    Container::ImplBlock(_) => {
-                        let substs = self.find_self_types(&def, ty.clone());
-
-                        self.write_assoc_resolution(id, item);
-                        Some((def, substs))
-                    }
+                let substs = match item.container(self.db) {
+                    Container::ImplBlock(_) => self.find_self_types(&def, ty.clone()),
                     Container::Trait(t) => {
                         // we're picking this method
                         let trait_substs = Substs::build_for_def(self.db, t)
@@ -217,11 +212,12 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                             trait_: t,
                             substs: trait_substs,
                         }));
-
-                        self.write_assoc_resolution(id, item);
-                        Some((def, Some(substs)))
+                        Some(substs)
                     }
-                }
+                };
+
+                self.write_assoc_resolution(id, item);
+                Some((def, substs))
             },
         )
     }
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index 8d682bb180..8c3d32d09d 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -166,12 +166,10 @@ pub(crate) fn lookup_method(
     name: &Name,
     resolver: &Resolver,
 ) -> Option<(Ty, Function)> {
-    iterate_method_candidates(ty, db, resolver, Some(name), LookupMode::MethodCall, |ty, f| {
-        if let AssocItem::Function(f) = f {
-            Some((ty.clone(), f))
-        } else {
-            None
-        }
+    iterate_method_candidates(ty, db, resolver, Some(name), LookupMode::MethodCall, |ty, f| match f
+    {
+        AssocItem::Function(f) => Some((ty.clone(), f)),
+        _ => None,
     })
 }
 
@@ -189,6 +187,7 @@ pub enum LookupMode {
 
 // This would be nicer if it just returned an iterator, but that runs into
 // lifetime problems, because we need to borrow temp `CrateImplBlocks`.
+// FIXME add a context type here?
 pub(crate) fn iterate_method_candidates<T>(
     ty: &Canonical<Ty>,
     db: &impl HirDatabase,