Needs documention: How to specify a certain version of Rust compiler?

[dnrusakov]

I went through the documentation and have not found:

1. how to specify a certain version of Rust compiler?
2. how to enable Rust nightly compiler?
   Thanks!

[damienmg]

The toolchains is specified using rust_toolchain.

They are defined on standard rust toolchain with: https://github.com/bazelbuild/rules_rust/blob/master/rust/repositories.bzl

So for using a specific version of the compiler you likely want to add a rules in your WORKSPACE file, e.g.:

rust_repository_set(
        name = "rust_linux_x86_64_nightly",
        exec_triple = "x86_64-unknown-linux-gnu",
        extra_target_triples = ["wasm32-unknown-unknown"],
        version = "nightly",
        rustfmt_version = "nightly",
 )

This needs more documentation.

If you do not use "rust_repositories", then it will probably just works with this other repo before the repository set:

load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

    maybe(
        http_archive,
        name = "rules_cc",
        url = "https://github.com/bazelbuild/rules_cc/archive/624b5d59dfb45672d4239422fa1e3de1822ee110.zip",
        sha256 = "8c7e8bf24a2bf515713445199a677ee2336e1c487fa1da41037c6026de04bbc3",
        strip_prefix = "rules_cc-624b5d59dfb45672d4239422fa1e3de1822ee110",
        type = "zip",
    )

If you specify the other, you might need to select the toolchain at the command line but I could not find a good answer on how to do that. Maybe @katre knows?

[DmitryRusakovKodiak]

@damienmg Thanks for the help!
I wonder, why RUST_VERSION is hard-coded inside def rust_repositories()? Shouldn't it be a parameter of the function, like, for example, def rust_repositories(rust_version, rust_fmt_version)?

[damienmg]

@DmitryRusakovKodiak yes I also think that should be parameters of the rust_repositories rule.

[katre]

Since rust_repository_set is calling native.register_toolchains, you shouldn't need any extra flags to make Bazel aware of the new toolchains. You may need to tweak the order of things, however, to ensure your new toolchain is higher priority than the standard toolchains.

[kragniz]

I made a start at this in #307

[nathanielford]

The rust_repositories(version = "nightly", iso_date = "2020-04-19") documentation does not seem to work with the previously mentioned configuration in the README's 'setup' section, due to the cited release not including the more recent version-specifying change. Might be worth updating to match?