rustdoc: add test for "Methods from Deref"

Author: lolbinarycat

tests/rustdoc/deref/deref-methods-24686-target.rs

@@ -0,0 +1,27 @@
+#![crate_name = "foo"]
+
+// test for https://github.com/rust-lang/rust/issues/24686
+use std::ops::Deref;
+
+pub struct Foo<T>(T);
+impl Foo<i32> {
+    pub fn get_i32(&self) -> i32 { self.0 }
+}
+impl Foo<u32> {
+    pub fn get_u32(&self) -> u32 { self.0 }
+}
+
+// Note that the same href is used both on the method itself,
+// and on the sidebar items.
+//@ has foo/struct.Bar.html
+//@ has - '//a[@href="#method.get_i32"]' 'get_i32'
+//@ !has - '//a[@href="#method.get_u32"]' 'get_u32'
+//@ count - '//ul[@class="block deref-methods"]//a' 1
+//@ count - '//a[@href="#method.get_i32"]' 2
+pub struct Bar(Foo<i32>);
+impl Deref for Bar {
+    type Target = Foo<i32>;
+    fn deref(&self) -> &Foo<i32> {
+        &self.0
+    }
+}