Rustdoc accessibility: use real headers for doc items

This is a pretty annoying workaround: the specifications literally
contradict each other on the matter of whether headers may be nested
inside of summaries. We need the headers for people who use outline
mode to browse rustdoc, mostly in screen readers, and the headers
need to be inside the summary tag so that they're visible when the
details tag is collapsed.

HTML5 says it's okay, but the ordinary button semantics in ARIA say
that headers nested in buttons are ignored, and summary is a button.
Which means some screen readers, like NVDA, work, while others,
like JAWS, don't.

src/librustdoc/html/render/mod.rs

@@ -1350,15 +1350,15 @@ fn render_impl(
                     );
                     render_rightside(w, cx, item, containing_item);
                     write!(w, "<a href=\"#{}\" class=\"anchor\"></a>", id);
-                    w.write_str("<code>");
+                    w.write_str("<h4 class=\"code-header\">");
                     render_assoc_item(
                         w,
                         item,
                         link.anchor(source_id.as_ref().unwrap_or(&id)),
                         ItemType::Impl,
                         cx,
                     );
-                    w.write_str("</code>");
+                    w.write_str("</h4>");
                     w.write_str("</div>");
                 }
             }
@@ -1371,7 +1371,7 @@ fn render_impl(
                     id, item_type, in_trait_class
                 );
                 write!(w, "<a href=\"#{}\" class=\"anchor\"></a>", id);
-                w.write_str("<code>");
+                w.write_str("<h4 class=\"code-header\">");
                 assoc_type(
                     w,
                     item,
@@ -1381,7 +1381,7 @@ fn render_impl(
                     "",
                     cx,
                 );
-                w.write_str("</code>");
+                w.write_str("</h4>");
                 w.write_str("</div>");
             }
             clean::AssocConstItem(ref ty, ref default) => {
@@ -1394,7 +1394,7 @@ fn render_impl(
                 );
                 render_rightside(w, cx, item, containing_item);
                 write!(w, "<a href=\"#{}\" class=\"anchor\"></a>", id);
-                w.write_str("<code>");
+                w.write_str("<h4 class=\"code-header\">");
                 assoc_const(
                     w,
                     item,
@@ -1404,15 +1404,15 @@ fn render_impl(
                     "",
                     cx,
                 );
-                w.write_str("</code>");
+                w.write_str("</h4>");
                 w.write_str("</div>");
             }
             clean::AssocTypeItem(ref bounds, ref default) => {
                 let source_id = format!("{}.{}", item_type, name);
                 let id = cx.derive_id(source_id.clone());
                 write!(w, "<div id=\"{}\" class=\"{}{}\">", id, item_type, in_trait_class,);
                 write!(w, "<a href=\"#{}\" class=\"anchor\"></a>", id);
-                w.write_str("<code>");
+                w.write_str("<h4 class=\"code-header\">");
                 assoc_type(
                     w,
                     item,
@@ -1422,7 +1422,7 @@ fn render_impl(
                     "",
                     cx,
                 );
-                w.write_str("</code>");
+                w.write_str("</h4>");
                 w.write_str("</div>");
             }
             clean::StrippedItem(..) => return,
@@ -1613,7 +1613,7 @@ pub(crate) fn render_impl_summary(
     write!(w, "<div id=\"{}\" class=\"impl has-srclink\"{}>", id, aliases);
     render_rightside(w, cx, &i.impl_item, containing_item);
     write!(w, "<a href=\"#{}\" class=\"anchor\"></a>", id);
-    write!(w, "<code class=\"in-band\">");
+    write!(w, "<h3 class=\"code-header in-band\">");
 
     if let Some(use_absolute) = use_absolute {
         write!(w, "{}", i.inner_impl().print(use_absolute, cx));
@@ -1629,7 +1629,7 @@ pub(crate) fn render_impl_summary(
     } else {
         write!(w, "{}", i.inner_impl().print(false, cx));
     }
-    write!(w, "</code>");
+    write!(w, "</h3>");
 
     let is_trait = i.inner_impl().trait_.is_some();
     if is_trait {

src/librustdoc/html/render/print_item.rs

@@ -621,9 +621,9 @@ fn item_trait(w: &mut Buffer, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
         render_stability_since(w, m, t, cx.tcx());
         write_srclink(cx, m, w);
         write!(w, "</div>");
-        write!(w, "<code>");
+        write!(w, "<h4 class=\"code-header\">");
         render_assoc_item(w, m, AssocItemLink::Anchor(Some(&id)), ItemType::Impl, cx);
-        w.write_str("</code>");
+        w.write_str("</h4>");
         w.write_str("</div>");
         if toggled {
             write!(w, "</summary>");

src/librustdoc/html/static/css/rustdoc.css

@@ -146,6 +146,13 @@ h1.fqn > .in-band > a:hover {
 h2, h3, h4 {
 	border-bottom: 1px solid;
 }
+h3.code-header, h4.code-header {
+	font-size: 1em;
+	font-weight: 600;
+	border: none;
+	padding: 0;
+	margin: 0;
+}
 .impl,
 .impl-items .method,
 .methods .method,
@@ -233,7 +240,7 @@ details:not(.rustdoc-toggle) summary {
 	margin-bottom: .6em;
 }
 
-code, pre, a.test-arrow {
+code, pre, a.test-arrow, .code-header {
 	font-family: "Source Code Pro", monospace;
 }
 .docblock code, .docblock-short code {
@@ -520,7 +527,7 @@ nav.sub {
 	font-weight: normal;
 }
 
-.method > code, .trait-impl > code, .invisible > code {
+.method > .code-header, .trait-impl > .code-header, .invisible > .code-header {
 	max-width: calc(100% - 41px);
 	display: block;
 }
@@ -536,7 +543,7 @@ nav.sub {
 	padding: 0px;
 }
 
-.in-band > code {
+.in-band > code, .in-band > .code-header {
 	display: inline-block;
 }
 
@@ -742,7 +749,7 @@ a {
 }
 
 .invisible > .srclink,
-.method > code + .srclink {
+.method > .code-header + .srclink {
 	position: absolute;
 	top: 0;
 	right: 0;
@@ -1103,7 +1110,7 @@ a.test-arrow:hover{
 	left: -10px;
 }
 
-:target > code {
+:target > code, :target > .code-header {
 	opacity: 1;
 }
 

src/librustdoc/html/static/js/main.js

@@ -706,8 +706,9 @@ function hideThemeButtonState() {
                     }
                 }
 
-                var code = document.createElement("code");
+                var code = document.createElement("h3");
                 code.innerHTML = struct.text;
+                addClass(code, "code-header");
                 addClass(code, "in-band");
 
                 onEachLazy(code.getElementsByTagName("a"), function(elem) {