Rollup merge of rust-lang#43979 - Jouan:Add-links-for-impls, r=GuillaumeGomez

Add links for impls

Implements a solution for issue rust-lang#23552
r? @QuietMisdreavus

Author: frewsxcv

src/librustdoc/html/render.rs

@@ -2956,7 +2956,13 @@ 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

@@ -445,6 +445,10 @@ a {
 .small-section-header:hover > .anchor {
 	display: initial;
 }
+
+.in-band:hover > .anchor {
+	display: initial;
+}
 .anchor {
 	display: none;
 }

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

@@ -26,6 +26,7 @@ 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;
 }
@@ -83,6 +84,11 @@ pre {
 }
 
 :target { background: #FDFFD3; }
+
+:target > .in-band {
+	background: #FDFFD3;
+}
+
 .content .highlighted {
 	color: #000 !important;
 	background-color: #ccc;