Rollup merge of rust-lang#88093 - Kobzol:rustdoc-wrap-code-in-code-tag, r=GuillaumeGomez

[rustdoc] Wrap code blocks in <code> tag

This PR modifies Rustdoc output so that fenced code snippets, items and whole file source codes are wrapped in `<pre><code>` instead of just `<pre>`. This should improve the semantic meaning of the generated content.

I'm not sure what to do about `render_attributes_in_pre` and `render_attributes_in_code`. These functions were clearly expected to be used for things inside `<pre>` or `<code>`, and since I added `<code>` in this PR, some of them will be used in a different context than before. However, it seems to me that even before they were not consistent. For example, `item_constant` used `render_attributes_in_code` for its attributes, however there was no `<code>` used for constants before this PR...

Should I create some `rustdoc-gui` tests? For example to check that all `<pre>` tags have a `<code>` child?

Fixes: rust-lang#88020

Author: GuillaumeGomez

src/librustdoc/html/highlight.rs

@@ -65,10 +65,11 @@ fn write_header(out: &mut Buffer, class: Option<&str>, extra_content: Option<Buf
         out.push_buffer(extra);
     }
     if let Some(class) = class {
-        writeln!(out, "<pre class=\"rust {}\">", class);
+        write!(out, "<pre class=\"rust {}\">", class);
     } else {
-        writeln!(out, "<pre class=\"rust\">");
+        write!(out, "<pre class=\"rust\">");
     }
+    write!(out, "<code>");
 }
 
 /// Convert the given `src` source code into HTML by adding classes for highlighting.
@@ -101,7 +102,7 @@ fn write_code(
 }
 
 fn write_footer(out: &mut Buffer, playground_button: Option<&str>) {
-    writeln!(out, "</pre>{}</div>", playground_button.unwrap_or_default());
+    writeln!(out, "</code></pre>{}</div>", playground_button.unwrap_or_default());
 }
 
 /// How a span of text is classified. Mostly corresponds to token kinds.

src/librustdoc/html/markdown.rs

@@ -234,7 +234,7 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for CodeBlocks<'_, 'a, I> {
                     return Some(Event::Html(
                         format!(
                             "<div class=\"example-wrap\">\
-                                 <pre class=\"language-{}\">{}</pre>\
+                                 <pre class=\"language-{}\"><code>{}</code></pre>\
                              </div>",
                             lang,
                             Escape(&text),