[src] links in rustdoc do not honor --extern-html-root-url

[QuietMisdreavus]

Originally reported at rust-lang/docs.rs#298

The crate mentioned in that issue has a #![doc(html_root_url)] attribute set, and the [src] link that points to that crate is using that to base its url. However, the --extern-html-root-url that docs.rs passes to rustdoc should be overriding that setting. We should investigate how rustdoc generates [src] links, and see whether it needs to be modified to account for --extern-html-root-url, like how other cross-crate links are made.

[GuillaumeGomez]

The whole thing happens in here and it seems the --extern-html-root-url option has priority over #![doc(html_root_url)]. Now my guess is: it's not given to sub-crates for some reason. Investigations continue!

[ollie27]

The build log shows rustdoc was passed --extern-html-root-url 'futures_util_preview=https://docs.rs/futures-util-preview/0.3.0-alpha.12' but the crate name is futures_util not futures_util_preview. It looks like docs.rs needs to use the actual crate name not the package name.

[QuietMisdreavus]

@ollie27 That makes sense! I'll reopen the issue on docs.rs and close this one (and @GuillaumeGomez's PR).