intra-rustdoc-link: Cannot use core in core crate

[tesuji]

I tried to document this code in libcore (./x.py doc src/libcore):

impl<T: Deref, E> Result<T, E> {
    /// Converts from `Result<T, E>` (or `&Result<T, E>`) to `Result<&<T as Deref>::Target, &E>`.
    ///
    /// [`core::ops::Deref`]
    pub fn as_deref(&self) -> Result<&T::Target, &E>;
}

I expected to see the above code build pass.

Instead, this happened: Build failed the following errors:

 Documenting core v0.0.0 (/home/lzutao/fork/rust/compiler/src/libcore)
error: `[core::ops::Deref]` cannot be resolved, ignoring it.
    --> src/libcore/result.rs:1151:68
     |
1151 |     /// Coerces the [`Ok`] variant of the original [`Result`] via [`core::ops::Deref`]
     |                                                                    ^^^^^^^^^^^^^^^^^^ cannot be resolved, ignoring
     |
note: the lint level is defined here
    --> src/libcore/lib.rs:64:9
     |
64   | #![deny(intra_doc_link_resolution_failure)] // rustdoc is run without -D warnings
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`

error: Could not document `core`.

cc #43466
cc @Manishearth @GuillaumeGomez @jyn514

[tesuji]

Note: Document build pass in user crate:

/// Intra link testings
///
/// [`Deref::Target`](core::ops::Deref)
pub struct Foo;

[jyn514]

What happens if you use crate::ops::Deref instead?

[jyn514]

Actually this might be a markdown issue, does [Deref::Target](core::ops::Deref) work in libcore?

[Manishearth]

@lzutao core::ops::Deref will never work in the core crate, crates do not know their own names typically

[Manishearth]

@jyn514 no, it's not a markdown issue

[jyn514]

@rustbot modify labels: T-rustdoc A-intra-doc-links D-confusing

[jplatte]

crates do not know their own names typically

Which can be worked around with an extern crate self as foo; in the crate root, in case anybody needs that (I've previously required it to get a proc macro working both inside its "parent crate" and outside of it).

[tesuji]

Oh, using [`crate::path`] works correctly. It is kind of confusing through.

[Manishearth]

I don't see how: cratename::foo never works in paths within the same crate

[tesuji]

I cannot use std:: doc link prefix also.

 Documenting core v0.0.0 (/home/lzutao/fork/rust/compiler/src/libcore)
error: `[std::ops::Deref]` cannot be resolved, ignoring it.
    --> src/libcore/result.rs:1151:77
     |
1151 |     /// Coerces the [`Ok`] variant of the original [`Result`] via [`Deref`](std::ops::Deref)
     |                                                                             ^^^^^^^^^^^^^^^ cannot be resolved, ignoring
     |

@Manishearth

cratename::foo never works in paths within the same crate

You have a point. But for me what makes this confusing is that in doctest
I have to import items by crate name. But in doc link I don't have to.