Add new test case showing that supertraits are not enough

Author: nikomatsakis

src/test/compile-fail/typeck-default-trait-impl-trait-where-clause.rs

@@ -0,0 +1,38 @@
+// 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.
+
+// Test that when a `..` impl applies, we also check that any
+// supertrait conditions are met.
+
+#![feature(optin_builtin_traits)]
+
+trait NotImplemented { }
+
+trait MyTrait
+    where Option<Self> : NotImplemented
+{}
+
+impl NotImplemented for i32 {}
+
+impl MyTrait for .. {}
+
+fn foo<T:MyTrait>() {
+    bar::<Option<T>>()
+        //~^ ERROR not implemented for the type `Option<T>`
+        //
+        // This should probably typecheck. This is #20671.
+}
+
+fn bar<T:NotImplemented>() { }
+
+fn main() {
+    foo::<i32>(); //~ ERROR not implemented for the type `i32`
+    bar::<Option<i32>>(); //~ ERROR not implemented for the type `Option<i32>`
+}