Use relative paths for std links in rustc-docs

[arferreira]

Fixes #151496

This adds --extern-html-root-url for each STD_PUBLIC_CRATES entry pointing to ../, so that rustc-docs links to the locally installed rust-docs via relative paths.

r? @GuillaumeGomez @rami3l

[GuillaumeGomez]

Thanks for the work! One thought I had: how do we test that? ^^'

[arferreira]

Thanks for the work! One thought I had: how do we test that? ^^'

Yeahh def! I tested manually, just built the compiler docs and comparing the HTML output before and after :)

[GuillaumeGomez]

I expect as much. :p

That was an open question for other rust contributors: how do we check that automatically in the CI to ensure it doesn't regress? Maybe you have an idea @Kobzol ?

[Kobzol]

What's the exact thing that you want to check? That all links in the docs are relative? Doesn't rustdoc already has some similar tests in one of its test suites?

[GuillaumeGomez]

Nah, just a few cross-crate ones. And we do, but it's unrelated here: we need this fix because std/core are handled differently and point to each others with https:// and not relative paths. What I want to check is that cross-crate links are using relative paths.

[Kobzol]

I guess it would either have to be some rustdoc test that scans the HTML (using some existing machinery), or it would require some large-ish changes. Because the docs that we dist are in the dist components, and we don't really have a notion of testing these today, outside of one hardcoded sanity checks for the PGO-ed rustc toolchain.

[GuillaumeGomez]

Nothing we can check then? Oh well, I guess I can live with that.

@bors r+ rollup

[rust-bors]

📌 Commit dcfc23a has been approved by GuillaumeGomez

It is now in the queue for this repository.