Warn unused type aliases

Author: sanxiyn

src/librustc/middle/dead.rs

@@ -89,13 +89,16 @@ impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
     fn lookup_and_handle_definition(&mut self, id: ast::NodeId) {
         let def = self.tcx.expect_def(id);
 
-        // If `bar` is a trait item, make sure to mark Foo as alive in `Foo::bar`
+        // If it is an associated item, mark the type as alive
         match def {
-            Def::AssociatedTy(..) | Def::Method(_) | Def::AssociatedConst(_)
-            if self.tcx.trait_of_item(def.def_id()).is_some() => {
-                if let Some(substs) = self.tcx.tables().item_substs.get(&id) {
-                    if let ty::TyAdt(tyid, _) = substs.substs.type_at(0).sty {
-                        self.check_def_id(tyid.did);
+            Def::AssociatedTy(..) | Def::Method(_) | Def::AssociatedConst(_) => {
+                if let Some(resolution) = self.tcx.assoc_map.get(&id) {
+                    let base_def = resolution.base_def;
+                    match base_def {
+                        Def::Struct(..) | Def::Enum(..) | Def::TyAlias(..) => {
+                            self.check_def_id(base_def.def_id());
+                        }
+                        _ => {}
                     }
                 }
             }
@@ -430,6 +433,7 @@ impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
             hir::ItemStatic(..)
             | hir::ItemConst(..)
             | hir::ItemFn(..)
+            | hir::ItemTy(..)
             | hir::ItemEnum(..)
             | hir::ItemStruct(..)
             | hir::ItemUnion(..) => true,

src/test/compile-fail/lint-dead-code-type-alias.rs

@@ -0,0 +1,20 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![deny(dead_code)]
+
+type Used = u8;
+type Unused = u8; //~ ERROR: type alias is never used
+
+fn id(x: Used) -> Used { x }
+
+fn main() {
+    id(0);
+}