Link no-deps documentation with no html_root_url to docs.rs by default

[dtolnay]

As of Rust 1.19.0-nightly, documenting a crate with cargo doc --no-deps will link to the html_root_url of any dependencies that have one set, and other dependencies will not be linked.

In the screenshot, the crate providing HasHtmlRootUrl has an html_root_url so the type is linked. The crate providing NoHtmlRootUrl does not have an html_root_url so the type is not linked.

Linking NoHtmlRootUrl to docs.rs would be a reasonable fallback.

[lnicola]

rustdoc can't check (presumably) that the crate really exists on docs.rs. Would it be reasonable to simply link to a page that might 404?

[lnicola]

I tried to look into this, but I couldn't figure out how to get the crate versions. The best I managed to do was linking to https://docs.rs/crate/*/crate, which loads the latest version (I assume). Of course, it won't work if the crate is not published, or if the versions are different.

Any other ideas?

[lily-mara]

It seems like possibly, rustdoc could get the version information from the Cargo.toml of the package, and make a request to https://docs.rs/crate/version/crate, and if it comes back with a 200, include a docs.rs link.

[anp]

It looks like rustdoc gained the ability to receive the flag from cargo: #51384, which I think would be the API to use. There's been some recent progress by @ehuss on letting cargo configure rustdoc more granularly, perhaps there's a solution in that direction?

[jyn514]

I tried to look into this, but I couldn't figure out how to get the crate versions. The best I managed to do was linking to https://docs.rs/crate/*/crate, which loads the latest version (I assume). Of course, it won't work if the crate is not published, or if the versions are different.

Any other ideas?

Rustdoc does not have access to the version of the crate, only the crate name. 'versions' are a cargo concept and the rust compiler/rustdoc don't know about them.

It seems like possibly, rustdoc could get the version information from the Cargo.toml of the package, and make a request to https://docs.rs/crate/version/crate, and if it comes back with a 200, include a docs.rs link.

I don't like rustdoc making network requests or having knowledge of cargo. You should be able to use rustdoc standalone, without internet access or a Cargo.toml.

With both of those things in mind, I think it makes more sense to delegate this to rust-lang/cargo#8296 instead.