Rollup merge of #103885 - fmease:rustdoc-various-cross-crate-reexport-fixes, r=cjgillot,GuillaumeGomez

rustdoc: various cross-crate reexport fixes

Fixes for various smaller cross-crate reexport issues.
The PR is split into several commits for easier review. Will be squashed after approval.

Most notable changes:

* We finally render late-bound lifetimes in the generic parameter list of cross-crate functions & methods.
  Previously, we would display the re-export of `pub fn f<'s>(x: &'s str) {}` as `pub fn f(x: &'s str)`
* We now render unnamed parameters of cross-crate functions and function pointers as underscores
  since that's exactly what we do for local definitions, too. Mentioned as a bug in #44306.
* From now on, the rendering of cross-crate trait-object types is more correct:
  * `for<>` parameter lists (for higher-ranked lifetimes) are now shown
  * the return type of `Fn{,Mut,Once}` trait bounds is now displayed

Regarding the last list item, here is a diff for visualization (before vs. after):

```patch
- dyn FnOnce(&'any str) + 'static
+ dyn for<'any> FnOnce(&'any str) -> bool + 'static
```

The redundant `+ 'static` will be removed in a follow-up PR that will hide trait-object lifetime-bounds if they coincide with [their default](https://doc.rust-lang.org/reference/lifetime-elision.html#default-trait-object-lifetimes) (see [Zulip discussion](https://rust-lang.zulipchat.com/#narrow/stream/266220-rustdoc/topic/clean_middle_ty.3A.20I.20need.20to.20add.20a.20parameter/near/307143097)). `FIXME(fmease)`s were added.

``@rustbot`` label A-cross-crate-reexports
r? ``@GuillaumeGomez``

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;
 }
 

src/test/rustdoc/inline_cross/assoc_item_trait_bounds.rs

@@ -33,8 +33,12 @@ extern crate assoc_item_trait_bounds as aux;
 // @snapshot out9 - '//*[@id="associatedtype.Out9"]/*[@class="code-header"]'
 //
 // @has - '//*[@id="tymethod.make"]' \
-// "fn make<F>(F, impl FnMut(&str) -> bool)\
+// "fn make<F>(_: F, _: impl FnMut(&str) -> bool)\
 // where \
 //     F: FnOnce(u32) -> String, \
 //     Self::Out2<()>: Protocol<u8, Q0 = Self::Item, Q1 = ()>"
 pub use aux::Main;
+
+// @has main/trait.Aid.html
+// @has - '//*[@id="associatedtype.Result"]' "type Result<'inter: 'src>"
+pub use aux::Aid;

src/test/rustdoc/inline_cross/auxiliary/assoc_item_trait_bounds.rs

@@ -42,5 +42,5 @@ pub trait Helper {
 }
 
 pub trait Aid<'src> {
-    type Result<'inter>;
+    type Result<'inter: 'src>;
 }

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> {}

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;

src/test/rustdoc/inline_cross/impl_trait.rs

@@ -29,7 +29,7 @@ pub use impl_trait_aux::func4;
 // @has impl_trait/fn.func5.html
 // @has - '//pre[@class="rust fn"]' "func5("
 // @has - '//pre[@class="rust fn"]' "_f: impl for<'any> Fn(&'any str, &'any str) -> bool + for<'r> Other<T<'r> = ()>,"
-// @has - '//pre[@class="rust fn"]' "_a: impl for<'alpha, 'beta> Auxiliary<'alpha, Item<'beta> = fn(&'beta ())>"
+// @has - '//pre[@class="rust fn"]' "_a: impl for<'alpha, 'beta> Auxiliary<'alpha, Item<'beta> = fn(_: &'beta ())>"
 // @!has - '//pre[@class="rust fn"]' 'where'
 pub use impl_trait_aux::func5;
 

src/test/rustdoc/issue-20727.rs

@@ -19,6 +19,6 @@ 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;"
+    //      "fn deref<'a>(&'a self) -> &'a Self::Target;"
     pub use issue_20727::Deref;
 }