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).

Author: notriddle

src/librustdoc/clean/types.rs

@@ -506,9 +506,6 @@ impl Item {
 pub(crate)fnis_mod(&self) -> bool{
 self.type_() == ItemType::Module
 }
-pub(crate)fnis_trait(&self) -> bool{
-self.type_() == ItemType::Trait
-}
 pub(crate)fnis_struct(&self) -> bool{
 self.type_() == ItemType::Struct
 }
@@ -536,9 +533,6 @@ impl Item {
 pub(crate)fnis_ty_method(&self) -> bool{
 self.type_() == ItemType::TyMethod
 }
-pub(crate)fnis_type_alias(&self) -> bool{
-self.type_() == ItemType::TypeAlias
-}
 pub(crate)fnis_primitive(&self) -> bool{
 self.type_() == ItemType::Primitive
 }

src/librustdoc/html/markdown.rs

@@ -55,7 +55,7 @@ use crate::html::format::Buffer;
 usecrate::html::highlight;
 usecrate::html::length_limit::HtmlWithLimit;
 usecrate::html::render::small_url_encode;
-usecrate::html::toc::TocBuilder;
+usecrate::html::toc::{Toc,TocBuilder};
 
 #[cfg(test)]
 mod tests;
@@ -101,6 +101,7 @@ pub struct Markdown<'a> {
 /// A struct like `Markdown` that renders the markdown with a table of contents.
 pub(crate)structMarkdownWithToc<'a>{
 pub(crate)content:&'astr,
+pub(crate)links:&'a[RenderedLink],
 pub(crate)ids:&'amutIdMap,
 pub(crate)error_codes:ErrorCodes,
 pub(crate)edition:Edition,
@@ -532,9 +533,9 @@ impl<'a, 'b, 'ids, I: Iterator<Item = SpannedEvent<'a>>> Iterator
 let id = self.id_map.derive(id);
 
 ifletSome(refmut builder) = self.toc{
-letmuthtml_header = String::new();
-html::push_html(&mut html_header,self.buf.iter().map(|(ev, _)| ev.clone()));
-let sec = builder.push(level asu32,html_header, id.clone());
+letmuttext_header = String::new();
+plain_text_from_events(self.buf.iter().map(|(ev, _)| ev.clone()),&mut text_header);
+let sec = builder.push(level asu32,text_header, id.clone());
 self.buf.push_front((Event::Html(format!("{sec} ").into()),0..0));
 }
 
@@ -1415,10 +1416,23 @@ impl Markdown<'_> {
 }
 
 implMarkdownWithToc<'_>{
-pub(crate)fninto_string(self) -> String{
-letMarkdownWithToc{content: md, ids,error_codes: codes, edition, playground } = self;
+pub(crate)fninto_parts(self) -> (Toc,String){
+letMarkdownWithToc{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());
+}
+letmut 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();
 
 letmut s = String::with_capacity(md.len()*3 / 2);
 
@@ -1432,7 +1446,11 @@ 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)fninto_string(self) -> String{
+let(toc, s) = self.into_parts();
+format!("<nav id=\"TOC\">{toc}</nav>{s}", toc = toc.print())
 }
 }
 
@@ -1611,7 +1629,16 @@ 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)fnplain_text_from_events<'a>(
+events:implIterator<Item = pulldown_cmark::Event<'a>>,
+s:&mutString,
+){
+for event in events {
 match&event {
 Event::Text(text) => s.push_str(text),
 Event::Code(code) => {
@@ -1626,8 +1653,6 @@ pub(crate) fn plain_text_summary(md: &str, link_names: &[RenderedLink]) -> Strin
  _ => (),
 }
 }
-
- s
 }
 
 #[derive(Debug)]

src/librustdoc/html/render/context.rs

@@ -616,7 +616,8 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
 let all = shared.all.replace(AllTypes::new());
 letmut 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(),&mutIdMap::new());
 let bar = Sidebar{
 title_prefix:"",
 title:"",