add auto-impl for primitive type

src/test/rustdoc/auto-impl-primitive.rs

@@ -0,0 +1,17 @@
+// Copyright 2018 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.
+
+#![crate_name = "foo"]
+pub use std::fs::File;
+
+// @has 'foo/primitive.i16.html' '//h2[@id="synthetic-implementations"]' 'Auto Trait Implementation'
+#[doc(primitive = "i16")]
+/// I love poneys!
+mod prim {}