rollup merge of #23117: japaric/default-impl

fixes #23080

r? @nikomatsakis
cc @flaper87

Author: alexcrichton

src/librustc_typeck/check/wf.rs

@@ -118,7 +118,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
 
                 self.check_variances_for_type_defn(item, ast_generics);
             }
-            ast::ItemTrait(_, ref ast_generics, _, _) => {
+            ast::ItemTrait(_, ref ast_generics, _, ref items) => {
                 let trait_predicates =
                     ty::lookup_predicates(ccx.tcx, local_def(item.id));
                 reject_non_type_param_bounds(
@@ -127,6 +127,14 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
                     &trait_predicates);
                 self.check_variances(item, ast_generics, &trait_predicates,
                                      self.tcx().lang_items.phantom_fn());
+                if ty::trait_has_default_impl(ccx.tcx, local_def(item.id)) {
+                    if !items.is_empty() {
+                        ccx.tcx.sess.span_err(
+                            item.span,
+                            "traits with default impls (`e.g. unsafe impl Trait for ..`) must \
+                            have no methods or associated items")
+                    }
+                }
             }
             _ => {}
         }

src/test/compile-fail/issue-23080-2.rs

@@ -0,0 +1,29 @@
+// Copyright 2015 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.
+
+// ignore-tidy-linelength
+
+#![feature(optin_builtin_traits)]
+
+use std::marker::MarkerTrait;
+
+unsafe trait Trait: MarkerTrait {
+//~^ error: traits with default impls (`e.g. unsafe impl Trait for ..`) must have no methods or associated items
+    type Output;
+}
+
+unsafe impl Trait for .. {}
+
+fn call_method<T: Trait>(x: T) {}
+
+fn main() {
+    // ICE
+    call_method(());
+}

src/test/compile-fail/issue-23080.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 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.
+
+// ignore-tidy-linelength
+
+#![feature(optin_builtin_traits)]
+
+unsafe trait Trait {
+//~^ error: traits with default impls (`e.g. unsafe impl Trait for ..`) must have no methods or associated items
+    fn method(&self) {
+        println!("Hello");
+    }
+}
+
+unsafe impl Trait for .. {}
+
+fn call_method<T: Trait>(x: T) {
+    x.method();
+}
+
+fn main() {
+    // ICE
+    call_method(());
+}