Accurately classify assoc. types in paths

crates/ide/src/goto_definition.rs

@@ -917,6 +917,21 @@ fn f() -> impl Iterator<Item$0 = u8> {}
         );
     }
 
+    #[test]
+    #[should_panic = "unresolved reference"]
+    fn unknown_assoc_ty() {
+        check(
+            r#"
+trait Iterator {
+    type Item;
+       //^^^^
+}
+
+fn f() -> impl Iterator<Invalid$0 = u8> {}
+            "#,
+        )
+    }
+
     #[test]
     fn goto_def_for_assoc_ty_in_path_multiple() {
         check(

crates/ide_db/src/defs.rs

@@ -330,12 +330,14 @@ impl NameRefClass {
             }
         }
 
-        if ast::AssocTypeArg::cast(parent.clone()).is_some() {
+        if let Some(assoc_type_arg) = ast::AssocTypeArg::cast(parent.clone()) {
+            if assoc_type_arg.name_ref().as_ref() == Some(name_ref) {
                 // `Trait<Assoc = Ty>`
                 //        ^^^^^
                 let path = name_ref.syntax().ancestors().find_map(ast::Path::cast)?;
                 let resolved = sema.resolve_path(&path)?;
                 if let PathResolution::Def(ModuleDef::Trait(tr)) = resolved {
+                    // FIXME: resolve in supertraits
                     if let Some(ty) = tr
                         .items(sema.db)
                         .iter()
@@ -350,6 +352,9 @@ impl NameRefClass {
                         )));
                     }
                 }
+
+                return None;
+            }
         }
 
         if let Some(macro_call) = parent.ancestors().find_map(ast::MacroCall::cast) {