Make new_without_default ignore const fns; fixes #977

clippy_lints/src/new_without_default.rs

@@ -95,7 +95,11 @@ fn check_fn(&mut self, cx: &LateContext, kind: FnKind, decl: &hir::FnDecl, _: &h
             return;
         }
 
-        if let FnKind::Method(name, _, _, _) = kind {
+        if let FnKind::Method(name, ref sig, _, _) = kind {
+            if sig.constness == hir::Constness::Const {
+                // can't be implemented by default
+                return;
+            }
             if decl.inputs.is_empty() && name.as_str() == "new" &&
                     cx.access_levels.is_reachable(id) {
                 let self_ty = cx.tcx.lookup_item_type(cx.tcx.map.local_def_id(

tests/compile-fail/new_without_default.rs

@@ -1,4 +1,4 @@
-#![feature(plugin)]
+#![feature(plugin, const_fn)]
 #![plugin(clippy)]
 
 #![allow(dead_code)]
@@ -70,4 +70,9 @@ impl Private {
     fn new() -> Private { unimplemented!() } // We don't lint private items
 }
 
+struct Const;
+
+impl Const {
+    pub const fn new() -> Const { Const } // const fns can't be implemented via Default
+}
 fn main() {}