Rustdoc regression: stable items reexported from unstable modules appear unstable

[tgross35]

Previously, stable items that are reexported from unstable modules (to stable modules) showed up as stable, which is correct because the user has a way to access them. However, since 1.83, they show up as unstable. This is accurate in one sense as they can't be stably accessed via the displayed path but is misleading because the types themselves are actually stably usable.

As an example, here is the most recent documentation from the most recent 1.83, as well as nightly https://doc.rust-lang.org/1.83.0/std/ffi/c_str/struct.FromBytesUntilNulError.html:

From 1.82 https://doc.rust-lang.org/1.82.0/std/ffi/c_str/struct.FromBytesUntilNulError.html:

And then 1.69, before it moved modules https://doc.rust-lang.org/1.69.0/core/ffi/struct.FromBytesUntilNulError.html:

There was a related issue in the near past with method signatures https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/Moving.20to.20a.20module.20breaks.20stability.20indicators

[tgross35]

One related thing: even though the type can be accessed stably, copying the path via the button gives a path that is only usable with unstable e.g. std::ffi::c_str::FromBytesUntilNulError. It may be nice to instead provide the fully stable path for anything that falls into this category (i.e. std::ffi::FromBytesUntilNulError).

[GrigorenkoPV]

For example, #134692 moves Mutex and MutexGuard to a new #[unstable] pub mod std::sync::poison.
They are then reexported with a #[stable] #[doc(inline)] pub use in std::sync.

However, a [`Mutex::lock`] link in the doc for MutexGuard gets resolved as std::sync::poison::Mutex::lock and not std::sync::Mutex::lock (same with try_lock in the screenshot above).

[notriddle]

The main ffi module shows the types as re-exported, instead of inlined.

https://doc.rust-lang.org/1.83.0/std/ffi/index.html#reexports

Re-exports

pub use self::c_str::FromBytesUntilNulError;

pub use self::c_str::FromBytesWithNulError;

pub use self::c_str::FromVecWithNulError;

pub use self::c_str::IntoStringError;

pub use self::c_str::NulError;

To fix that, the use statements need marked with #[doc(inline)]. Fixing this, as in returning to the status quo, seems weird. After all, they aren't accessible at the path given.