rustdoc: add test for cross-crate trait-object types

as well as some FIXMEs

Author: fmease

Diff for: src/librustdoc/clean/mod.rs

@@ -1683,6 +1683,9 @@ pub(crate) fn clean_middle_ty<'tcx>(
 
             inline::record_extern_fqn(cx, did, ItemType::Trait);
 
+            // FIXME(fmease): Hide the trait-object lifetime bound if it coincides with its default
+            // to partially address #44306. Follow the rules outlined at
+            // https://doc.rust-lang.org/reference/lifetime-elision.html#default-trait-object-lifetimes
             let lifetime = clean_middle_region(*reg);
             let mut bounds = dids
                 .map(|did| {

Diff for: src/test/rustdoc/assoc-consts.rs

@@ -46,6 +46,7 @@ pub fn f(_: &(ToString + 'static)) {}
 impl Bar {
     // @has assoc_consts/struct.Bar.html '//*[@id="associatedconstant.F"]' \
     //      "const F: fn(_: &(dyn ToString + 'static))"
+    // FIXME(fmease): Hide default lifetime, render "const F: fn(_: &dyn ToString)"
     pub const F: fn(_: &(ToString + 'static)) = f;
 }
 

Diff for: src/test/rustdoc/inline_cross/auxiliary/dyn_trait.rs

@@ -0,0 +1,17 @@
+pub type Ty0 = dyn for<'any> FnOnce(&'any str) -> bool;
+
+pub type Ty1<'obj> = dyn std::fmt::Display + 'obj;
+
+pub type Ty2 = dyn for<'a, 'r> Container<'r, Item<'a, 'static> = ()>;
+
+pub type Ty3<'s> = &'s dyn ToString;
+
+pub fn func0(_: &(dyn Fn() + '_)) {}
+
+pub fn func1<'func>(_: &(dyn Fn() + 'func)) {}
+
+pub trait Container<'r> {
+    type Item<'a, 'ctx>;
+}
+
+pub trait Shape<'a> {}

Diff for: src/test/rustdoc/inline_cross/dyn_trait.rs

@@ -0,0 +1,31 @@
+#![crate_name = "user"]
+
+// aux-crate:dyn_trait=dyn_trait.rs
+// edition:2021
+
+// @has user/type.Ty0.html
+// @has - '//*[@class="item-decl"]//code' "dyn for<'any> FnOnce(&'any str) -> bool + 'static"
+// FIXME(fmease): Hide default lifetime bound `'static`
+pub use dyn_trait::Ty0;
+
+// @has user/type.Ty1.html
+// @has - '//*[@class="item-decl"]//code' "dyn Display + 'obj"
+pub use dyn_trait::Ty1;
+
+// @has user/type.Ty2.html
+// @has - '//*[@class="item-decl"]//code' "dyn for<'a, 'r> Container<'r, Item<'a, 'static> = ()>"
+pub use dyn_trait::Ty2;
+
+// @has user/type.Ty3.html
+// @has - '//*[@class="item-decl"]//code' "&'s (dyn ToString + 's)"
+// FIXME(fmease): Hide default lifetime bound, render "&'s dyn ToString"
+pub use dyn_trait::Ty3;
+
+// @has user/fn.func0.html
+// @has - '//pre[@class="rust fn"]' "func0(_: &dyn Fn())"
+// FIXME(fmease): Show placeholder-lifetime bound, render "func0(_: &(dyn Fn() + '_))"
+pub use dyn_trait::func0;
+
+// @has user/fn.func1.html
+// @has - '//pre[@class="rust fn"]' "func1<'func>(_: &(dyn Fn() + 'func))"
+pub use dyn_trait::func1;