rustdoc: Improve handling inlined associated types

* All bounds are now discovered through the trait to be inlined.
* The `?Sized` bound now renders correctly for inlined associated types.
* All `QPath`s (`<A as B>::C`) instances are rendered as `A::C` where `C` is a
  hyperlink to the trait `B`. This should improve at least how the docs look at
  least.
* Supertrait bounds are now separated and display as the source lists them.

Closes #20727
Closes #21145

src/test/auxiliary/issue-20727.rs

@@ -0,0 +1,38 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub trait Deref {
+    type Target: ?Sized;
+
+    fn deref<'a>(&'a self) -> &'a Self::Target;
+}
+
+pub trait Add<RHS = Self> {
+    type Output;
+
+    fn add(self, rhs: RHS) -> Self::Output;
+}
+
+
+pub trait Bar {}
+pub trait Deref2 {
+    type Target: Bar;
+
+    fn deref(&self) -> Self::Target;
+}
+
+pub trait Index<Idx: ?Sized> {
+    type Output: ?Sized;
+    fn index(&self, index: Idx) -> &Self::Output;
+}
+
+pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
+    fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
+}

src/test/rustdoc/issue-20727-2.rs

@@ -0,0 +1,32 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// aux-build:issue-20727.rs
+
+extern crate issue_20727;
+
+// @has issue_20727_2/trait.Add.html
+pub trait Add<RHS = Self> {
+    // @has - '//*[@class="rust trait"]' 'trait Add<RHS = Self> {'
+    // @has - '//*[@class="rust trait"]' 'type Output;'
+    type Output;
+
+    // @has - '//*[@class="rust trait"]' 'fn add(self, rhs: RHS) -> Self::Output;'
+    fn add(self, rhs: RHS) -> Self::Output;
+}
+
+// @has issue_20727_2/reexport/trait.Add.html
+pub mod reexport {
+    // @has - '//*[@class="rust trait"]' 'trait Add<RHS = Self> {'
+    // @has - '//*[@class="rust trait"]' 'type Output;'
+    // @has - '//*[@class="rust trait"]' 'fn add(self, rhs: RHS) -> Self::Output;'
+    pub use issue_20727::Add;
+}
+

src/test/rustdoc/issue-20727-3.rs

@@ -0,0 +1,33 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// aux-build:issue-20727.rs
+
+extern crate issue_20727;
+
+pub trait Bar {}
+
+// @has issue_20727_3/trait.Deref2.html
+pub trait Deref2 {
+    // @has - '//*[@class="rust trait"]' 'trait Deref2 {'
+    // @has - '//*[@class="rust trait"]' 'type Target: Bar;'
+    type Target: Bar;
+
+    // @has - '//*[@class="rust trait"]' 'fn deref(&self) -> Self::Target;'
+    fn deref(&self) -> Self::Target;
+}
+
+// @has issue_20727_3/reexport/trait.Deref2.html
+pub mod reexport {
+    // @has - '//*[@class="rust trait"]' 'trait Deref2 {'
+    // @has - '//*[@class="rust trait"]' 'type Target: Bar;'
+    // @has - '//*[@class="rust trait"]' 'fn deref(&self) -> Self::Target;'
+    pub use issue_20727::Deref2;
+}

src/test/rustdoc/issue-20727-4.rs

@@ -0,0 +1,49 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// aux-build:issue-20727.rs
+
+extern crate issue_20727;
+
+// @has issue_20727_4/trait.Index.html
+pub trait Index<Idx: ?Sized> {
+    // @has - '//*[@class="rust trait"]' 'trait Index<Idx: ?Sized> {'
+    // @has - '//*[@class="rust trait"]' 'type Output: ?Sized'
+    type Output: ?Sized;
+
+    // @has - '//*[@class="rust trait"]' \
+    //        'fn index(&self, index: Idx) -> &Self::Output'
+    fn index(&self, index: Idx) -> &Self::Output;
+}
+
+// @has issue_20727_4/trait.IndexMut.html
+pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
+    // @has - '//*[@class="rust trait"]' \
+    //        'trait IndexMut<Idx: ?Sized>: Index<Idx> {'
+    // @has - '//*[@class="rust trait"]' \
+    //        'fn index_mut(&mut self, index: Idx) -> &mut Self::Output;'
+    fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
+}
+
+pub mod reexport {
+    // @has issue_20727_4/reexport/trait.Index.html
+    // @has - '//*[@class="rust trait"]' 'trait Index<Idx> where Idx: ?Sized {'
+    // @has - '//*[@class="rust trait"]' 'type Output: ?Sized'
+    // @has - '//*[@class="rust trait"]' \
+    //        'fn index(&self, index: Idx) -> &Self::Output'
+    pub use issue_20727::Index;
+
+    // @has issue_20727_4/reexport/trait.IndexMut.html
+    // @has - '//*[@class="rust trait"]' \
+    //        'trait IndexMut<Idx>: Index<Idx> where Idx: ?Sized {'
+    // @has - '//*[@class="rust trait"]' \
+    //        'fn index_mut(&mut self, index: Idx) -> &mut Self::Output;'
+    pub use issue_20727::IndexMut;
+}

src/test/rustdoc/issue-20727.rs

@@ -0,0 +1,33 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// aux-build:issue-20727.rs
+
+extern crate issue_20727;
+
+// @has issue_20727/trait.Deref.html
+pub trait Deref {
+    // @has - '//*[@class="rust trait"]' 'trait Deref {'
+    // @has - '//*[@class="rust trait"]' 'type Target: ?Sized;'
+    type Target: ?Sized;
+
+    // @has - '//*[@class="rust trait"]' \
+    //        "fn deref<'a>(&'a self) -> &'a Self::Target;"
+    fn deref<'a>(&'a self) -> &'a Self::Target;
+}
+
+// @has issue_20727/reexport/trait.Deref.html
+pub mod reexport {
+    // @has - '//*[@class="rust trait"]' 'trait Deref {'
+    // @has - '//*[@class="rust trait"]' 'type Target: ?Sized;'
+    // @has - '//*[@class="rust trait"]' \
+    //      "fn deref(&'a self) -> &'a Self::Target;"
+    pub use issue_20727::Deref;
+}