Add regression test for implementations displayed on reference primitive type

Author: GuillaumeGomez

src/test/rustdoc/primitive-reference.rs

@@ -0,0 +1,37 @@
+#![crate_name = "foo"]
+
+#![feature(rustdoc_internals)]
+
+// @has foo/index.html
+// @has - '//h2[@id="primitives"]' 'Primitive Types'
+// @has - '//a[@href="primitive.reference.html"]' 'reference'
+// @has - '//div[@class="sidebar-elems"]//li/a' 'Primitive Types'
+// @has - '//div[@class="sidebar-elems"]//li/a/@href' '#primitives'
+// @has foo/primitive.reference.html
+// @has - '//a[@class="primitive"]' 'reference'
+// @has - '//span[@class="in-band"]' 'Primitive Type reference'
+// @has - '//section[@id="main-content"]//div[@class="docblock"]//p' 'this is a test!'
+
+// There should be only one implementation listed.
+// @count - '//*[@class="impl has-srclink"]' 1
+// @has - '//*[@id="impl-Foo%3C%26A%3E-for-%26B"]/*[@class="code-header in-band"]' \
+//        'impl<A, B> Foo<&A> for &B'
+#[doc(primitive = "reference")]
+/// this is a test!
+mod reference {}
+
+pub struct Bar;
+
+// This implementation should **not** show up.
+impl<T> From<&T> for Bar {
+    fn from(s: &T) -> Self {
+        Bar
+    }
+}
+
+pub trait Foo<T> {
+    fn stuff(&self, other: &T) {}
+}
+
+// This implementation should show up.
+impl<A, B> Foo<&A> for &B {}