`cargo doc -Zbuild-std` doesn't generate links to the standard library

[jyn514]

See for example https://docs.rs/gba/latest/gba/macro.include_aligned_bytes.html.

@nemo157 and I think this is because std doesn't have html_root_url set and cargo doesn't treat it as coming from crates.io, so -Zrustdoc-map doesn't help. The fix is for cargo to internally pass -Zcrate-attr=doc(html_root_url=https://doc.rust-lang.org/stable/std), like bootstrap does: https://github.com/rust-lang/rust/blob/871b5952023139738f72eba235063575062bc2e9/src/bootstrap/compile.rs#L416-L419

[ehuss]

Just curious, which of these behaviors would you expect to be the default, and which would you like the option of using?

1. Link to https://doc.rust-lang.org/<channel>/
2. Link to local docs installed via rustup
3. Generate documentation for std in the local target folder and link to it there (like it was any other dependency)

[Lokathor]

I'd expect docs.rs to use (1), I'm not sure about local docs. Maybe I'd still expect (1) by default?

[jyn514]

Hmm. docs.rs uses --no-deps, so it needs 1 to at least be an option - i would be ok with manually passing --extern-html-root-url there if you don't want to support it in cargo.

I'd expect 3. to be the behavior without --no-deps. I think with no-deps I'd expect 2. to be the default with a fallback to 1. if rust-docs isn't installed.

[Lokathor]

Since this is specifically for build-std, rust-src will always be installed (edit: or if someone is silly enough to try and doc a crate they couldn't build on that same machine, it seems fine to just error out)

[Nemo157]

I think with no-deps I'd expect 2. to be the default with a fallback to 1. if rust-src isn't installed.

I assume this was meant to be rust-docs not rust-src.