Website does not show if a crate has been yanked

[jyn514]

e.g. https://docs.rs/actix-web/0.7.10 looks like a normal release while https://crates.io/crates/actix-web/0.7.10 shows that it's been yanked.

[jyn514]

I think the proper thing to do here is to treat is like a failed build: redirect to /crate/:crate/:version and put a big warning that says it's been yanked, along with a link to the most recent successful version.

[jyn514]

Fixed by #739