Higher-Rank Trait Bounds (HRTB) not properly rendered

[Enselic]

Comparing the rustdoc HTML output of https://github.com/rust-lang/rust/blob/master/src/test/rustdoc/higher-ranked-trait-bounds.rs with the output of public-api, there are differences. To see them, first generate rustdoc HTML output for that file:

% ~/.rustup/toolchains/nightly-2022-03-31-aarch64-apple-darwin/bin/rustdoc ~/src/rust/src/test/rustdoc/higher-ranked-trait-bounds.rs -Z unstable-options --output-format html -o /tmp/hrtb

and then look at e.g. open /tmp/hrtb/foo/fn.test3.html which looks like this:

pub fn test3<F>() 
where
    F: for<'a, 'b> Fn(&'a u8, &'b u8), 

and then generate output with public-api:

% ~/.rustup/toolchains/nightly-2022-03-31-aarch64-apple-darwin/bin/rustdoc ~/src/rust/src/test/rustdoc/higher-ranked-trait-bounds.rs -Z unstable-options --output-format json -o /tmp/hrtb
% public-api /tmp/hrtb/foo.json 
pub fn foo::Foo::bar<T>() where T: Trait<'a>
pub fn foo::test1<T>() where &'a T: Iterator
pub fn foo::test2<T>() where &'a T: Trait<'b>
pub fn foo::test3<F>() where F: Fn(&'a u8, &'b u8)<'a, 'b>
pub mod foo
pub struct field foo::Bar::bar: &'a Trait<'b> + Unpin
pub struct field foo::Bar::baz: &'a Unpin + Trait<'b><'b>
pub struct field foo::Foo::some_func: fn(&'c i32) -> i32
pub struct field foo::Foo::some_trait: &'a Trait<'b>
pub struct foo::Bar<'a>
pub struct foo::Foo<'a>
pub trait foo::B<'x>
pub trait foo::Trait<'x>

Normalizing whitespace and linewlines and aligning, we have this vs that:

pub fn      test3<F>() where F: for<'a, 'b> Fn(&'a u8, &'b u8), 
pub fn foo::test3<F>() where F:             Fn(&'a u8, &'b u8)<'a, 'b>

There is a FIXME related to HRTB in rust-lang/rust/src/librustdoc/json/conversions.rs, so not sure we can fix them all, but it looks like we can fix the particular example I brought up.

For reference HRTB, didn't work properly in rustdoc HTML either for quite a while (see rust-lang/rust#78482), but was fixed quite recently, which also added the FIXME (see rust-lang/rust#84814).

To fix HRTBs in rustdoc HTML, the DynTrait object was introduced in the above PR. So fixing all HRTB problems might be related to fixing cargo-public-api/cargo-public-api#40, in case it requires upstream changes.

[Enselic]

We are waiting on a change to rustdoc JSON, see rust-lang/rust#96647.

[Enselic]

Closed by #92. I believe remaining HRTB related work can be scoped to cargo-public-api/cargo-public-api#40