Mention versioned rustup-init binary URLs

[apodolsk]

https://forge.rust-lang.org/infra/other-installation-methods.html#other-ways-to-install-rustup should probably mention that it's possible to download specific versions of rustup-init binaries, via the versioned download links mentioned in the similar docs at https://rust-lang.github.io/rustup/installation/other.html#manual-installation.

I noticed this because I'm trying to set up a reproducible build for a rust toolchain at my company. https://www.rust-lang.org/tools/install links to https://forge.rust-lang.org/infra/other-installation-methods.html, so this seems to be the most authoritative version of the install instructions. And these instructions currently suggest only the unversioned rustup-init URLS, which are presumably not fit for a reproducible build because they're going to get updated over time to point to the latest builds.

[apiraino]

In the documentation page you mention I read:

To get a previous version, use https://static.rust-lang.org/rustup/archive/{rustup-version}/{target-triple}/rustup-init[.exe].

You mean to make it more prominent? Do you want to submit a patch?

[apodolsk]

Well, yes, but I only mentioned the page that you linked as the "good" example. The same information is missing from the "bad version" of the rustup install instructions at https://forge.rust-lang.org/infra/other-installation-methods.html#other-ways-to-install-rustup. And it's the forge page that is linked from https://www.rust-lang.org/tools/install, not the rustup-specific page. It took me quite a few "surely version URLs must exist somewhere"-fueled attempts at googling to find the rustup-specific page.

I'm proposing copying that snippet (and the SHA256sums note) from the rustup-specific page onto the forge page.

If that sounds OK, and no one thinks that e.g. some bigger change is in order (like linking to the rustup-specific page, rather than trying to mirror its content), then I can submit the change.

[ChrisDenton]

The new simpler way to download a specific version will be using the RUSTUP_VERSION environment variable (see rust-lang/rustup#4259). However, this isn't yet released and manual downloads will still be supported when it is.

To be honest though I'm not sure that we should be linking users to the rust forge. These are internal docs meant for rustc devs (or potential contributors). It might be better to reorganise the website(s) to better surface the information for end users.