have different docs for nightly/beta/stable channels

[matthiaskrgr]

Currently clippy suggestion urls point to mostly the same page regardless of rustc release channel

stable:

    = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#unreadable_literal

beta:

    = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/master/index.html#unnecessary_mut_passed

nightly:

    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unreadable_literal

If a lint gets removed/downgraded in the current master branch and the docs get updates, the clippy version used on stable might not reflect this but still points to the master docs.
I think we need separate docs for nightly/stable/beta branches of the compiler.
Perhaps we can use separate branches for each release (like 1.30) or channel?

[matthiaskrgr]

Perhaps we could solve this by universally baking the current commit hash into the url used by the docs, but then again I think docs are not regenerated on every commit?

[matthiaskrgr]

Or we could probably fix this by sort of pinning the clippy version to the one of rustc so that version-specific docs are released for every rustc channel.
clippy 0.0.212-1.30

[oli-obk]

Or we could probably fix this by sort of pinning the clippy version to the one of rustc so that version-specific docs are released for every rustc channel.

That's what I implemented, but it's not working

[matthiaskrgr]

fn docs_link(diag: &mut DiagnosticBuilder<'_>, lint: &'static Lint) {
    if env::var("CLIPPY_DISABLE_DOCS_LINKS").is_err() {
        if let Some(lint) = lint.name_lower().strip_prefix("clippy::") {
            diag.help(&format!(
                "for further information visit https://rust-lang.github.io/rust-clippy/{}/index.html#{}",
                &option_env!("RUST_RELEASE_NUM").map_or("master".to_string(), |n| {
                    // extract just major + minor version and ignore patch versions
                    format!("rust-{}", n.rsplitn(2, '.').nth(1).unwrap())
                }),
                lint
            ));
        }
    }
}

No idea where RUST_RELEASE_NUM is coming from, it does not seem to be documented anywhere 😆
Is there a replacement for that?