Rollup merge of #117869 - GuillaumeGomez:comment-highlighting-item-decl, r=notriddle

[rustdoc] Add highlighting for comments in items declaration

Fixes #117555.

So after the discussion in https://github.com/rust-lang/rust/pull/117643, the outcome was that having the comments in the item declaration at the same level (in term of color) as the rest of the code was actually a bit distracting and could be improved.

The current highlighting color for comments is "lighter" than the rest and I think it fits perfectly to improve the current situation. With this, we now have different "levels" which makes it easier to read and filter out what we want when reading the items declaration.

Here's a screenshot:

![image](https://github.com/rust-lang/rust/assets/3050060/dbd98029-e98b-4997-9a89-6b823eaac9a4)

r? `@notriddle`

1 files changed, 14 insertions, 8 deletions

diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index e4309c782f6..131b1d608e6 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -1509,7 +1509,7 @@ fn print_tuple_struct_fields<'a, 'cx: 'a>(
                 matches!(*field.kind, clean::StrippedItem(box clean::StructFieldItem(..)))
             })
         {
-            return f.write_str("/* private fields */");
+            return f.write_str("<span class=\"comment\">/* private fields */</span>");
         }
 
         for (i, ty) in s.iter().enumerate() {
@@ -1666,7 +1666,7 @@ fn render_enum_fields(
         }
 
         if variants_stripped && !is_non_exhaustive {
-            w.write_str("    // some variants omitted\n");
+            w.write_str("    <span class=\"comment\">// some variants omitted</span>\n");
         }
         if toggle {
             toggle_close(&mut w);
@@ -1811,7 +1811,8 @@ fn item_proc_macro(
         let name = it.name.expect("proc-macros always have names");
         match m.kind {
             MacroKind::Bang => {
-                write!(buffer, "{name}!() {{ /* proc-macro */ }}").unwrap();
+                write!(buffer, "{name}!() {{ <span class=\"comment\">/* proc-macro */</span> }}")
+                    .unwrap();
             }
             MacroKind::Attr => {
                 write!(buffer, "#[{name}]").unwrap();
@@ -1819,7 +1820,12 @@ fn item_proc_macro(
             MacroKind::Derive => {
                 write!(buffer, "#[derive({name})]").unwrap();
                 if !m.helpers.is_empty() {
-                    buffer.write_str("\n{\n    // Attributes available to this derive:\n").unwrap();
+                    buffer
+                        .write_str(
+                            "\n{\n    \
+                        <span class=\"comment\">// Attributes available to this derive:</span>\n",
+                        )
+                        .unwrap();
                     for attr in &m.helpers {
                         writeln!(buffer, "    #[{attr}]").unwrap();
                     }
@@ -2181,7 +2187,7 @@ fn render_union<'a, 'cx: 'a>(
         }
 
         if it.has_stripped_entries().unwrap() {
-            write!(f, "    /* private fields */\n")?;
+            write!(f, "    <span class=\"comment\">/* private fields */</span>\n")?;
         }
         if toggle {
             toggle_close(&mut f);
@@ -2267,11 +2273,11 @@ fn render_struct_fields(
 
             if has_visible_fields {
                 if has_stripped_entries {
-                    write!(w, "\n{tab}    /* private fields */");
+                    write!(w, "\n{tab}    <span class=\"comment\">/* private fields */</span>");
                 }
                 write!(w, "\n{tab}");
             } else if has_stripped_entries {
-                write!(w, " /* private fields */ ");
+                write!(w, " <span class=\"comment\">/* private fields */</span> ");
             }
             if toggle {
                 toggle_close(&mut w);
@@ -2285,7 +2291,7 @@ fn render_struct_fields(
                     matches!(*field.kind, clean::StrippedItem(box clean::StructFieldItem(..)))
                 })
             {
-                write!(w, "/* private fields */");
+                write!(w, "<span class=\"comment\">/* private fields */</span>");
             } else {
                 for (i, field) in fields.iter().enumerate() {
                     if i > 0 {