rustdoc hangs on recursive associated types

[theemathas]

I tried this code:

trait Bar {
    type Element: Bar;
}

struct Foo<T: Bar>(T, *const Foo<T::Element>);

This code compiles fine with cargo build. However, running cargo doc causes it to hang.

Likely related to rust-lang/rust-clippy#13544 and #133356

Discovered by super_surviveur on the rust official discord.

Meta

rustc --version --verbose:

rustc 1.88.0-nightly (78f2104e3 2025-04-16)
binary: rustc
commit-hash: 78f2104e334068d5a892a170d50193c0025c690e
commit-date: 2025-04-16
host: aarch64-apple-darwin
release: 1.88.0-nightly
LLVM version: 20.1.2

@rustbot labels +T-rustdoc +I-hang

[matthiaskrgr]

Duplicate of #102910 ?

[theemathas]

Unlike #102910, this code compiles fine without issue, but only fails with cargo doc.

[fmease]

At the time of writing the next trait solver seems to fix this. Not sure if that's coincidental/spurious or proper. Let's see.

[theemathas]

@fmease How are you invoking the next trait solver? I used the following command and rustdoc still hangs:

RUSTFLAGS='-Znext-solver=globally' cargo +nightly doc

Edit: nvm, it needs to be:

RUSTDOCFLAGS='-Znext-solver=globally' cargo +nightly doc