cmd/godoc: Add anchor links to functions, types and methods

Added anchor link beside each function, type and method definition in
godoc's generated HTML.  Anchor links are only shown when the mouse is
hovering over the definition.  The link body is the Unicode PILCROW SIGN
character (¶ HTML entity).

Fixes: golang/go#13748

Change-Id: I645269f6c229f76b2882899e1a7483577877ac30
Reviewed-on: https://go-review.googlesource.com/20246
Reviewed-by: Andrew Gerrand <adg@golang.org>

Author: nwidger

godoc/static/package.html

@@ -165,7 +165,9 @@ <h2 id="pkg-variables">Variables</h2>
 		{{range .Funcs}}
 			{{/* Name is a string - no need for FSet */}}
 			{{$name_html := html .Name}}
-			<h2 id="{{$name_html}}">func <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a></h2>
+			<h2 id="{{$name_html}}">func <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a>
+				<a class="permalink" href="#{{$name_html}}">&#xb6;</a>
+			</h2>
 			<pre>{{node_html $ .Decl true}}</pre>
 			{{comment_html .Doc}}
 			{{example_html $ .Name}}
@@ -175,7 +177,9 @@ <h2 id="{{$name_html}}">func <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a
 		{{range .Types}}
 			{{$tname := .Name}}
 			{{$tname_html := html .Name}}
-			<h2 id="{{$tname_html}}">type <a href="{{posLink_url $ .Decl}}">{{$tname_html}}</a></h2>
+			<h2 id="{{$tname_html}}">type <a href="{{posLink_url $ .Decl}}">{{$tname_html}}</a>
+				<a class="permalink" href="#{{$tname_html}}">&#xb6;</a>
+			</h2>
 			<pre>{{node_html $ .Decl true}}</pre>
 			{{comment_html .Doc}}
 
@@ -195,7 +199,9 @@ <h2 id="{{$tname_html}}">type <a href="{{posLink_url $ .Decl}}">{{$tname_html}}<
 
 			{{range .Funcs}}
 				{{$name_html := html .Name}}
-				<h3 id="{{$name_html}}">func <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a></h3>
+				<h3 id="{{$name_html}}">func <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a>
+					<a class="permalink" href="#{{$tname_html}}">&#xb6;</a>
+				</h3>
 				<pre>{{node_html $ .Decl true}}</pre>
 				{{comment_html .Doc}}
 				{{example_html $ .Name}}
@@ -204,7 +210,9 @@ <h3 id="{{$name_html}}">func <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a
 
 			{{range .Methods}}
 				{{$name_html := html .Name}}
-				<h3 id="{{$tname_html}}.{{$name_html}}">func ({{html .Recv}}) <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a></h3>
+				<h3 id="{{$tname_html}}.{{$name_html}}">func ({{html .Recv}}) <a href="{{posLink_url $ .Decl}}">{{$name_html}}</a>
+					<a class="permalink" href="#{{$tname_html}}.{{$name_html}}">&#xb6;</a>
+				</h3>
 				<pre>{{node_html $ .Decl true}}</pre>
 				{{comment_html .Doc}}
 				{{$name := printf "%s_%s" $tname .Name}}

godoc/static/static.go

@@ -42,6 +42,14 @@ a:hover,
 .exampleHeading .text:hover {
 	text-decoration: underline;
 }
+
+.permalink {
+	display: none;
+}
+h2:hover .permalink, h3:hover .permalink {
+	display: inline;
+}
+
 p, li {
 	max-width: 800px;
 	word-wrap: break-word;