Rollup merge of #49427 - Manishearth:rustdoc-impl-trait-extern, r=GuillaumeGomez

Correctly handle impl trait in external items in rustdoc

fixes #49373

r? @QuietMisdreavus

src/test/rustdoc/auxiliary/extern-impl-trait.rs

@@ -0,0 +1,37 @@
+// Copyright 2018 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 Foo {
+    type Associated;
+}
+
+pub struct X;
+pub struct Y;
+
+
+impl Foo for X {
+    type Associated = ();
+}
+
+impl Foo for Y {
+    type Associated = ();
+}
+
+impl X {
+    pub fn returns_sized<'a>(&'a self) -> impl Foo<Associated=()> + 'a {
+        X
+    }
+}
+
+impl Y {
+    pub fn returns_unsized<'a>(&'a self) -> Box<impl ?Sized + Foo<Associated=()> + 'a> {
+        Box::new(X)
+    }
+}

src/test/rustdoc/extern-impl-trait.rs

@@ -0,0 +1,21 @@
+// Copyright 2018 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:extern-impl-trait.rs
+
+#![crate_name = "foo"]
+
+extern crate extern_impl_trait;
+
+// @has 'foo/struct.X.html' '//code' "impl Foo<Associated = ()> + 'a"
+pub use extern_impl_trait::X;
+
+// @has 'foo/struct.Y.html' '//code' "impl ?Sized + Foo<Associated = ()> + 'a"
+pub use extern_impl_trait::Y;