Add links for impls

Implements a solution for issue #23552

src/librustdoc/html/render.rs

@@ -2925,7 +2925,13 @@ fn render_deref_methods(w: &mut fmt::Formatter, cx: &Context, impl_: &Impl,
 fn render_impl(w: &mut fmt::Formatter, cx: &Context, i: &Impl, link: AssocItemLink,
                render_mode: RenderMode, outer_version: Option<&str>) -> fmt::Result {
     if render_mode == RenderMode::Normal {
-        write!(w, "<h3 class='impl'><span class='in-band'><code>{}</code>", i.inner_impl())?;
+        let id = derive_id(match i.inner_impl().trait_ {
+            Some(ref t) => format!("impl-{}", Escape(&format!("{:#}", t))),
+            None => "impl".to_string(),
+        });
+        write!(w, "<h3 id='{}' class='impl'><span class='in-band'><code>{}</code>",
+               id, i.inner_impl())?;
+        write!(w, "<a href='#{}' class='anchor'></a>", id)?;
         write!(w, "</span><span class='out-of-band'>")?;
         let since = i.impl_item.stability.as_ref().map(|s| &s.since[..]);
         if let Some(l) = (Item { item: &i.impl_item, cx: cx }).src_href() {

src/librustdoc/html/static/rustdoc.css

@@ -441,6 +441,10 @@ a {
 .small-section-header:hover > .anchor {
 	display: initial;
 }
+
+.in-band:hover > .anchor {
+	display: initial;
+}
 .anchor {
 	display: none;
 }

src/librustdoc/html/static/styles/main.css

@@ -26,9 +26,6 @@ h1.fqn {
 h2, h3:not(.impl):not(.method):not(.type):not(.tymethod), h4:not(.method):not(.type):not(.tymethod) {
 	border-bottom-color: #DDDDDD;
 }
-.in-band {
-	background-color: white;
-}
 
 .docblock code, .docblock-short code {
 	background-color: #F5F5F5;