Derive Default instead of new in applicable lint

src/librustc_lint/builtin.rs

@@ -542,18 +542,13 @@ declare_lint! {
     "detects missing implementations of fmt::Debug"
 }
 
+#[derive(Default)]
 pub struct MissingDebugImplementations {
     impling_types: Option<HirIdSet>,
 }
 
 impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
 
-impl MissingDebugImplementations {
-    pub fn new() -> MissingDebugImplementations {
-        MissingDebugImplementations { impling_types: None }
-    }
-}
-
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDebugImplementations {
     fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
         if !cx.access_levels.is_reachable(item.hir_id) {

src/librustc_lint/lib.rs

@@ -132,7 +132,7 @@ macro_rules! late_lint_passes {
             // Depends on access levels
             // FIXME: Turn the computation of types which implement Debug into a query
             // and change this to a module lint pass
-            MissingDebugImplementations: MissingDebugImplementations::new(),
+            MissingDebugImplementations: MissingDebugImplementations::default(),
         ]);
     )
 }