Account for trait alias when looking for defid

Author: tesuji

clippy_lints/src/methods/mod.rs

@@ -2781,7 +2781,10 @@ impl SelfKind {
                 hir::Mutability::MutMutable => &paths::ASMUT_TRAIT,
             };
 
-            let trait_def_id = get_trait_def_id(cx, trait_path).expect("trait def id not found");
+            let trait_def_id = match get_trait_def_id(cx, trait_path) {
+                Some(did) => did,
+                None => return false,
+            };
             implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
         }
 

clippy_lints/src/utils/mod.rs

@@ -261,14 +261,16 @@ pub fn path_to_res(cx: &LateContext<'_, '_>, path: &[&str]) -> Option<(def::Res)
 }
 
 /// Convenience function to get the `DefId` of a trait by path.
+/// It could be a trait or trait alias.
 pub fn get_trait_def_id(cx: &LateContext<'_, '_>, path: &[&str]) -> Option<DefId> {
     let res = match path_to_res(cx, path) {
         Some(res) => res,
         None => return None,
     };
 
     match res {
-        def::Res::Def(DefKind::Trait, trait_id) => Some(trait_id),
+        Res::Def(DefKind::Trait, trait_id) | Res::Def(DefKind::TraitAlias, trait_id) => Some(trait_id),
+        Res::Err => unreachable!("this trait resolution is impossible: {:?}", &path),
         _ => None,
     }
 }