Rollup merge of #42594 - ollie27:rustdoc_assoc_type_links, r=steveklabnik

rustdoc: Link directly to associated types

Rather than just linking to the trait.

Also simplifies the logic used to decide whether to render the full
QPath.

Author: frewsxcv

src/librustdoc/html/format.rs

@@ -459,22 +459,10 @@ pub fn href(did: DefId) -> Option<(String, ItemType, Vec<String>)> {
 /// rendering function with the necessary arguments for linking to a local path.
 fn resolved_path(w: &mut fmt::Formatter, did: DefId, path: &clean::Path,
                  print_all: bool, use_absolute: bool) -> fmt::Result {
-    let empty = clean::PathSegment {
-                    name: String::new(),
-                    params: clean::PathParameters::Parenthesized {
-                        inputs: Vec::new(),
-                        output: None,
-                    }
-                };
-    let last = path.segments.last()
-                            .unwrap_or(&empty);
-    let rel_root = if path.segments.is_empty() {
-        None
-    } else {
-        match &*path.segments[0].name {
-            "self" => Some("./".to_string()),
-            _ => None,
-        }
+    let last = path.segments.last().unwrap();
+    let rel_root = match &*path.segments[0].name {
+        "self" => Some("./".to_string()),
+        _ => None,
     };
 
     if print_all {
@@ -508,7 +496,7 @@ fn resolved_path(w: &mut fmt::Formatter, did: DefId, path: &clean::Path,
                 Some((_, _, fqp)) => {
                     format!("{}::{}",
                             fqp[..fqp.len() - 1].join("::"),
-                            HRef::new(did, fqp.last().unwrap_or(&String::new())))
+                            HRef::new(did, fqp.last().unwrap()))
                 }
                 None => format!("{}", HRef::new(did, &last.name)),
             }
@@ -740,10 +728,8 @@ fn fmt_type(t: &clean::Type, f: &mut fmt::Formatter, use_absolute: bool) -> fmt:
         }
         clean::QPath { ref name, ref self_type, ref trait_ } => {
             let should_show_cast = match *trait_ {
-                box clean::ResolvedPath { .. } => {
-                    let path = clean::Path::singleton(name.clone());
-                    !path.segments.is_empty() && &format!("{:#}", trait_) != "()" &&
-                    &format!("{:#}", self_type) != "Self"
+                box clean::ResolvedPath { ref path, .. } => {
+                    !path.segments.is_empty() && !self_type.is_self_type()
                 }
                 _ => true,
             };
@@ -772,8 +758,18 @@ fn fmt_type(t: &clean::Type, f: &mut fmt::Formatter, use_absolute: bool) -> fmt:
                 //        everything comes in as a fully resolved QPath (hard to
                 //        look at).
                 box clean::ResolvedPath { did, ref typarams, .. } => {
-                    let path = clean::Path::singleton(name.clone());
-                    resolved_path(f, did, &path, true, use_absolute)?;
+                    match href(did) {
+                        Some((ref url, _, ref path)) if !f.alternate() => {
+                            write!(f,
+                                   "<a class=\"type\" href=\"{url}#{shortty}.{name}\" \
+                                   title=\"type {path}::{name}\">{name}</a>",
+                                   url = url,
+                                   shortty = ItemType::AssociatedType,
+                                   name = name,
+                                   path = path.join("::"))?;
+                        }
+                        _ => write!(f, "{}", name)?,
+                    }
 
                     // FIXME: `typarams` are not rendered, and this seems bad?
                     drop(typarams);

src/test/rustdoc/assoc-types.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// ignore-tidy-linelength
+
 #![crate_type="lib"]
 
 // @has assoc_types/trait.Index.html
@@ -18,11 +20,14 @@ pub trait Index<I: ?Sized> {
     // @has - '//*[@id="index.v"]//code' 'fn index'
     // @has - '//*[@id="tymethod.index"]//code' \
     //      "fn index<'a>(&'a self, index: I) -> &'a Self::Output"
+    // @has - '//*[@id="tymethod.index"]//code//a[@href="../assoc_types/trait.Index.html#associatedtype.Output"]' \
+    //      "Output"
     fn index<'a>(&'a self, index: I) -> &'a Self::Output;
 }
 
 // @has assoc_types/fn.use_output.html
 // @has - '//*[@class="rust fn"]' '-> &T::Output'
+// @has - '//*[@class="rust fn"]//a[@href="../assoc_types/trait.Index.html#associatedtype.Output"]' 'Output'
 pub fn use_output<T: Index<usize>>(obj: &T, index: usize) -> &T::Output {
     obj.index(index)
 }
@@ -33,10 +38,12 @@ pub trait Feed {
 
 // @has assoc_types/fn.use_input.html
 // @has - '//*[@class="rust fn"]' 'T::Input'
+// @has - '//*[@class="rust fn"]//a[@href="../assoc_types/trait.Feed.html#associatedtype.Input"]' 'Input'
 pub fn use_input<T: Feed>(_feed: &T, _element: T::Input) { }
 
 // @has assoc_types/fn.cmp_input.html
 // @has - '//*[@class="rust fn"]' 'where T::Input: PartialEq<U::Input>'
+// @has - '//*[@class="rust fn"]//a[@href="../assoc_types/trait.Feed.html#associatedtype.Input"]' 'Input'
 pub fn cmp_input<T: Feed, U: Feed>(a: &T::Input, b: &U::Input) -> bool
     where T::Input: PartialEq<U::Input>
 {