Resolve intra-doc links in summary desc

Before:

![rustdoc-intra-doc-link-summary-before](https://user-images.githubusercontent.com/1593513/122623069-9d995e80-d04f-11eb-8d46-ec2ec126bb5e.png)

After:

![rustdoc-intra-doc-link-summary](https://user-images.githubusercontent.com/1593513/122623076-a4c06c80-d04f-11eb-967a-f5916871c34b.png)

src/librustdoc/clean/types.rs

@@ -523,6 +523,33 @@ impl Item {
             .collect()
     }
 
+    /// Find a list of all link names, without finding their href.
+    ///
+    /// This is used for generating summary text, which does not include
+    /// the link text, but does need to know which `[]`-bracketed names
+    /// are actually links.
+    crate fn link_names(&self, cache: &Cache) -> Vec<RenderedLink> {
+        cache
+            .intra_doc_links
+            .get(&self.def_id)
+            .map_or(&[][..], |v| v.as_slice())
+            .iter()
+            .filter_map(|ItemLink { link: s, link_text, did, fragment }| {
+                // FIXME(83083): using fragments as a side-channel for
+                // primitive names is very unfortunate
+                if did.is_some() || fragment.is_some() {
+                    Some(RenderedLink {
+                        original_text: s.clone(),
+                        new_text: link_text.clone(),
+                        href: String::new(),
+                    })
+                } else {
+                    None
+                }
+            })
+            .collect()
+    }
+
     crate fn is_crate(&self) -> bool {
         self.is_mod() && self.def_id.as_real().map_or(false, |did| did.index == CRATE_DEF_INDEX)
     }

src/librustdoc/formats/cache.rs

@@ -292,13 +292,14 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
                     // which should not be indexed. The crate-item itself is
                     // inserted later on when serializing the search-index.
                     if item.def_id.index().map_or(false, |idx| idx != CRATE_DEF_INDEX) {
+                        let desc = item.doc_value().map_or_else(String::new, |x| {
+                            short_markdown_summary(&x.as_str(), &item.link_names(&self.cache))
+                        });
                         self.cache.search_index.push(IndexItem {
                             ty: item.type_(),
                             name: s.to_string(),
                             path: path.join("::"),
-                            desc: item
-                                .doc_value()
-                                .map_or_else(String::new, |x| short_markdown_summary(&x.as_str())),
+                            desc,
                             parent,
                             parent_idx: None,
                             search_type: get_index_search_type(&item, &self.empty_cache, self.tcx),

src/librustdoc/html/markdown.rs

@@ -1051,7 +1051,11 @@ impl MarkdownSummaryLine<'_> {
 ///
 /// Returns a tuple of the rendered HTML string and whether the output was shortened
 /// due to the provided `length_limit`.
-fn markdown_summary_with_limit(md: &str, length_limit: usize) -> (String, bool) {
+fn markdown_summary_with_limit(
+    md: &str,
+    link_names: &[RenderedLink],
+    length_limit: usize,
+) -> (String, bool) {
     if md.is_empty() {
         return (String::new(), false);
     }
@@ -1065,7 +1069,20 @@ fn markdown_summary_with_limit(md: &str, length_limit: usize) -> (String, bool)
         *text_length += text.len();
     }
 
-    'outer: for event in Parser::new_ext(md, summary_opts()) {
+    let mut replacer = |broken_link: BrokenLink<'_>| {
+        if let Some(link) =
+            link_names.iter().find(|link| &*link.original_text == broken_link.reference)
+        {
+            Some((link.href.as_str().into(), link.new_text.as_str().into()))
+        } else {
+            None
+        }
+    };
+
+    let p = Parser::new_with_broken_link_callback(md, opts(), Some(&mut replacer));
+    let p = LinkReplacer::new(p, link_names);
+
+    'outer: for event in p {
         match &event {
             Event::Text(text) => {
                 for word in text.split_inclusive(char::is_whitespace) {
@@ -1121,8 +1138,8 @@ fn markdown_summary_with_limit(md: &str, length_limit: usize) -> (String, bool)
 /// Will shorten to 59 or 60 characters, including an ellipsis (…) if it was shortened.
 ///
 /// See [`markdown_summary_with_limit`] for details about what is rendered and what is not.
-crate fn short_markdown_summary(markdown: &str) -> String {
-    let (mut s, was_shortened) = markdown_summary_with_limit(markdown, 59);
+crate fn short_markdown_summary(markdown: &str, link_names: &[RenderedLink]) -> String {
+    let (mut s, was_shortened) = markdown_summary_with_limit(markdown, link_names, 59);
 
     if was_shortened {
         s.push('…');

src/librustdoc/html/render/cache.rs

@@ -34,11 +34,14 @@ crate fn build_index<'tcx>(krate: &clean::Crate, cache: &mut Cache, tcx: TyCtxt<
     // has since been learned.
     for &(did, ref item) in &cache.orphan_impl_items {
         if let Some(&(ref fqp, _)) = cache.paths.get(&did) {
+            let desc = item
+                .doc_value()
+                .map_or_else(String::new, |s| short_markdown_summary(&s, &item.link_names(&cache)));
             cache.search_index.push(IndexItem {
                 ty: item.type_(),
                 name: item.name.unwrap().to_string(),
                 path: fqp[..fqp.len() - 1].join("::"),
-                desc: item.doc_value().map_or_else(String::new, |s| short_markdown_summary(&s)),
+                desc,
                 parent: Some(did.into()),
                 parent_idx: None,
                 search_type: get_index_search_type(&item, cache, tcx),
@@ -47,6 +50,11 @@ crate fn build_index<'tcx>(krate: &clean::Crate, cache: &mut Cache, tcx: TyCtxt<
         }
     }
 
+    let crate_doc = krate
+        .module
+        .doc_value()
+        .map_or_else(String::new, |s| short_markdown_summary(&s, &krate.module.link_names(&cache)));
+
     let Cache { ref mut search_index, ref paths, .. } = *cache;
 
     // Aliases added through `#[doc(alias = "...")]`. Since a few items can have the same alias,
@@ -100,9 +108,6 @@ crate fn build_index<'tcx>(krate: &clean::Crate, cache: &mut Cache, tcx: TyCtxt<
         crate_items.push(&*item);
     }
 
-    let crate_doc =
-        krate.module.doc_value().map_or_else(String::new, |s| short_markdown_summary(&s));
-
     struct CrateData<'a> {
         doc: String,
         items: Vec<&'a IndexItem>,