Add Top TOC support to rustdoc

This commit adds the headers for the top level documentation to
rustdoc's existing table of contents, along with associated items.

It only show two levels of headers. Going further would require the
sidebar to be wider, and that seems unnecessary (the crates that
have manually-built TOCs usually don't need deeply nested headers).

src/librustdoc/clean/types.rs

@@ -511,9 +511,6 @@ impl Item {
     pub(crate) fn is_mod(&self) -> bool {
         self.type_() == ItemType::Module
     }
-    pub(crate) fn is_trait(&self) -> bool {
-        self.type_() == ItemType::Trait
-    }
     pub(crate) fn is_struct(&self) -> bool {
         self.type_() == ItemType::Struct
     }
@@ -541,9 +538,6 @@ impl Item {
     pub(crate) fn is_ty_method(&self) -> bool {
         self.type_() == ItemType::TyMethod
     }
-    pub(crate) fn is_type_alias(&self) -> bool {
-        self.type_() == ItemType::TypeAlias
-    }
     pub(crate) fn is_primitive(&self) -> bool {
         self.type_() == ItemType::Primitive
     }

src/librustdoc/html/markdown.rs

@@ -51,7 +51,7 @@ use crate::html::format::Buffer;
 use crate::html::highlight;
 use crate::html::length_limit::HtmlWithLimit;
 use crate::html::render::small_url_encode;
-use crate::html::toc::TocBuilder;
+use crate::html::toc::{Toc, TocBuilder};
 
 use pulldown_cmark::{
     html, BrokenLink, BrokenLinkCallback, CodeBlockKind, CowStr, Event, LinkType, OffsetIter,
@@ -102,6 +102,7 @@ pub struct Markdown<'a> {
 /// A struct like `Markdown` that renders the markdown with a table of contents.
 pub(crate) struct MarkdownWithToc<'a> {
     pub(crate) content: &'a str,
+    pub(crate) links: &'a [RenderedLink],
     pub(crate) ids: &'a mut IdMap,
     pub(crate) error_codes: ErrorCodes,
     pub(crate) edition: Edition,
@@ -531,9 +532,9 @@ impl<'a, 'b, 'ids, I: Iterator<Item = SpannedEvent<'a>>> Iterator
             let id = self.id_map.derive(id);
 
             if let Some(ref mut builder) = self.toc {
-                let mut html_header = String::new();
-                html::push_html(&mut html_header, self.buf.iter().map(|(ev, _)| ev.clone()));
-                let sec = builder.push(level as u32, html_header, id.clone());
+                let mut text_header = String::new();
+                plain_text_from_events(self.buf.iter().map(|(ev, _)| ev.clone()), &mut text_header);
+                let sec = builder.push(level as u32, text_header, id.clone());
                 self.buf.push_front((Event::Html(format!("{sec} ").into()), 0..0));
             }
 
@@ -1396,10 +1397,23 @@ impl Markdown<'_> {
 }
 
 impl MarkdownWithToc<'_> {
-    pub(crate) fn into_string(self) -> String {
-        let MarkdownWithToc { content: md, ids, error_codes: codes, edition, playground } = self;
+    pub(crate) fn into_parts(self) -> (Toc, String) {
+        let MarkdownWithToc { content: md, links, ids, error_codes: codes, edition, playground } =
+            self;
 
-        let p = Parser::new_ext(md, main_body_opts()).into_offset_iter();
+        // This is actually common enough to special-case
+        if md.is_empty() {
+            return (Toc { entries: Vec::new() }, String::new());
+        }
+        let mut replacer = |broken_link: BrokenLink<'_>| {
+            links
+                .iter()
+                .find(|link| &*link.original_text == &*broken_link.reference)
+                .map(|link| (link.href.as_str().into(), link.tooltip.as_str().into()))
+        };
+
+        let p = Parser::new_with_broken_link_callback(md, main_body_opts(), Some(&mut replacer));
+        let p = p.into_offset_iter();
 
         let mut s = String::with_capacity(md.len() * 3 / 2);
 
@@ -1413,7 +1427,11 @@ impl MarkdownWithToc<'_> {
             html::push_html(&mut s, p);
         }
 
-        format!("<nav id=\"TOC\">{toc}</nav>{s}", toc = toc.into_toc().print())
+        (toc.into_toc(), s)
+    }
+    pub(crate) fn into_string(self) -> String {
+        let (toc, s) = self.into_parts();
+        format!("<nav id=\"TOC\">{toc}</nav>{s}", toc = toc.print())
     }
 }
 
@@ -1592,7 +1610,16 @@ pub(crate) fn plain_text_summary(md: &str, link_names: &[RenderedLink]) -> Strin
 
     let p = Parser::new_with_broken_link_callback(md, summary_opts(), Some(&mut replacer));
 
-    for event in p {
+    plain_text_from_events(p, &mut s);
+
+    s
+}
+
+pub(crate) fn plain_text_from_events<'a>(
+    events: impl Iterator<Item = pulldown_cmark::Event<'a>>,
+    s: &mut String,
+) {
+    for event in events {
         match &event {
             Event::Text(text) => s.push_str(text),
             Event::Code(code) => {
@@ -1607,8 +1634,6 @@ pub(crate) fn plain_text_summary(md: &str, link_names: &[RenderedLink]) -> Strin
             _ => (),
         }
     }
-
-    s
 }
 
 #[derive(Debug)]

src/librustdoc/html/render/context.rs

@@ -626,7 +626,8 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
         let all = shared.all.replace(AllTypes::new());
         let mut sidebar = Buffer::html();
 
-        let blocks = sidebar_module_like(all.item_sections());
+        // all.html is not customizable, so a blank id map is fine
+        let blocks = sidebar_module_like(all.item_sections(), &mut IdMap::new());
         let bar = Sidebar {
             title_prefix: "",
             title: "",