rustdoc: use <wbr> in sidebar

This also improves sidebar layout, so instead of

    BTreeM
    ap

you get this

    BTree
    Map

src/librustdoc/html/render/sidebar.rs

@@ -76,6 +76,22 @@ impl<'a> Link<'a> {
     }
 }
 
+pub(crate) mod filters {
+    use crate::{html::escape::EscapeBodyTextWithWbr, html::render::display_fn};
+    use askama::{Html, MarkupDisplay};
+    use std::fmt::Display;
+    pub(crate) fn wrapped<T>(v: T) -> askama::Result<MarkupDisplay<Html, impl Display>>
+    where
+        T: Display,
+    {
+        let string = v.to_string();
+        Ok(MarkupDisplay::new_safe(
+            display_fn(move |f| EscapeBodyTextWithWbr(&string).fmt(f)),
+            Html,
+        ))
+    }
+}
+
 pub(super) fn print_sidebar(cx: &Context<'_>, it: &clean::Item, buffer: &mut Buffer) {
     let blocks: Vec<LinkBlock<'_>> = match *it.kind {
         clean::StructItem(ref s) => sidebar_struct(cx, it, s),

src/librustdoc/html/templates/sidebar.html

@@ -15,12 +15,14 @@ <h2 class="location"> {# #}
             {% for block in blocks %}
                 {% if block.should_render() %}
                     {% if !block.heading.name.is_empty() %}
-                        <h3><a href="#{{block.heading.href|safe}}">{{block.heading.name}}</a></h3>
+                        <h3><a href="#{{block.heading.href|safe}}"> {# #}
+                            {{block.heading.name|wrapped|safe}} {# #}
+                        </a></h3> {# #}
                     {% endif %}
                     {% if !block.links.is_empty() %}
                         <ul class="block{% if !block.class.is_empty() +%} {{+block.class}}{% endif %}">
                             {% for link in block.links %}
-                                <li><a href="#{{link.href|safe}}">{{link.name}}</a></li>
+                                <li><a href="#{{link.href|safe}}">{{link.name|wrapped|safe}}</a></li>
                             {% endfor %}
                         </ul>
                     {% endif %}