rustdoc: add more tooltips to intra-doc links

This commit makes intra-doc link tooltips consistent with generated
links in function signatures and item tables, with the format
`itemtype foo::bar::baz`. This way, you can tell if a link points at
a trait or a type (for example) by mousing over it.

See also fce944d4e79b3a87ddf511206724edf33acfd704

2 files changed, 27 insertions, 5 deletions

diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 8a7a8ea5fd1..314f0612249 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -34,6 +34,7 @@ use crate::clean::{
 use crate::formats::item_type::ItemType;
 use crate::html::escape::Escape;
 use crate::html::render::Context;
+use crate::passes::collect_intra_doc_links::UrlFragment;
 
 use super::url_parts_builder::estimate_item_path_byte_length;
 use super::url_parts_builder::UrlPartsBuilder;
@@ -768,6 +769,21 @@ pub(crate) fn href_relative_parts<'fqp>(
     }
 }
 
+pub(crate) fn link_tooltip(did: DefId, fragment: &Option<UrlFragment>, cx: &Context<'_>) -> String {
+    let cache = cx.cache();
+    let Some((fqp, shortty)) = cache.paths.get(&did)
+        .or_else(|| cache.external_paths.get(&did))
+        else { return String::new() };
+    let fqp = fqp.iter().map(|sym| sym.as_str()).join("::");
+    if let &Some(UrlFragment::Item(id)) = fragment {
+        let name = cx.tcx().item_name(id);
+        let descr = cx.tcx().def_kind(id).descr(id);
+        format!("{descr} {fqp}::{name}")
+    } else {
+        format!("{shortty} {fqp}")
+    }
+}
+
 /// Used to render a [`clean::Path`].
 fn resolved_path<'cx>(
     w: &mut fmt::Formatter<'_>,
diff --git a/src/librustdoc/html/markdown.rs b/src/librustdoc/html/markdown.rs
index 33180439393..e4adee6ae4d 100644
--- a/src/librustdoc/html/markdown.rs
+++ b/src/librustdoc/html/markdown.rs
@@ -360,6 +360,9 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
                     trace!("it matched");
                     assert!(self.shortcut_link.is_none(), "shortcut links cannot be nested");
                     self.shortcut_link = Some(link);
+                    if title.is_empty() && !link.tooltip.is_empty() {
+                        *title = CowStr::Borrowed(link.tooltip.as_ref());
+                    }
                 }
             }
             // Now that we're done with the shortcut link, don't replace any more text.
@@ -410,9 +413,12 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
             }
             // If this is a link, but not a shortcut link,
             // replace the URL, since the broken_link_callback was not called.
-            Some(Event::Start(Tag::Link(_, dest, _))) => {
+            Some(Event::Start(Tag::Link(_, dest, title))) => {
                 if let Some(link) = self.links.iter().find(|&link| *link.original_text == **dest) {
                     *dest = CowStr::Borrowed(link.href.as_ref());
+                    if title.is_empty() && !link.tooltip.is_empty() {
+                        *title = CowStr::Borrowed(link.tooltip.as_ref());
+                    }
                 }
             }
             // Anything else couldn't have been a valid Rust path, so no need to replace the text.
@@ -976,7 +982,7 @@ impl Markdown<'_> {
             links
                 .iter()
                 .find(|link| link.original_text.as_str() == &*broken_link.reference)
-                .map(|link| (link.href.as_str().into(), link.new_text.as_str().into()))
+                .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));
@@ -1059,7 +1065,7 @@ impl MarkdownSummaryLine<'_> {
             links
                 .iter()
                 .find(|link| link.original_text.as_str() == &*broken_link.reference)
-                .map(|link| (link.href.as_str().into(), link.new_text.as_str().into()))
+                .map(|link| (link.href.as_str().into(), link.tooltip.as_str().into()))
         };
 
         let p = Parser::new_with_broken_link_callback(md, summary_opts(), Some(&mut replacer))
@@ -1106,7 +1112,7 @@ fn markdown_summary_with_limit(
         link_names
             .iter()
             .find(|link| link.original_text.as_str() == &*broken_link.reference)
-            .map(|link| (link.href.as_str().into(), link.new_text.as_str().into()))
+            .map(|link| (link.href.as_str().into(), link.tooltip.as_str().into()))
     };
 
     let p = Parser::new_with_broken_link_callback(md, summary_opts(), Some(&mut replacer));
@@ -1187,7 +1193,7 @@ pub(crate) fn plain_text_summary(md: &str, link_names: &[RenderedLink]) -> Strin
         link_names
             .iter()
             .find(|link| link.original_text.as_str() == &*broken_link.reference)
-            .map(|link| (link.href.as_str().into(), link.new_text.as_str().into()))
+            .map(|link| (link.href.as_str().into(), link.tooltip.as_str().into()))
     };
 
     let p = Parser::new_with_broken_link_callback(md, summary_opts(), Some(&mut replacer));