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From:   Adam Bratschi-Kaye <ark.email@gmail.com>
Date:   Mon, 22 Mar 2021 09:22:41 +0100
Message-ID: <CAHaybgkt0jy_G8cO88CJ9H2MiiakqfZGjAo3f37056amLPhcEg@mail.gmail.com>
Subject: Re: drivers/char/rust_example fails to load 2021-03-20 builds
To:     Geert Stappers <stappers@stappers.nl>
Cc:     Joshua Abraham <j.abraham1776@gmail.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        rust-for-linux@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
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> How to tell "use older parts in toolchain"?
> Yeah, probably a Rust newbie question, still a sincere question.
> Was a older version installed? How to tell `rustup` to keep old
> versions? Was done with a cargo.toml entry? Or with file
> `rust-toolchain`?  Please tell   (Please spoon feed me ;-)

Using `rust-toolchain.toml` should work.
Another option would be to override the default version for the given
directory with
`rustup override set nightly-2021-02-20`.

You could also set the global default `rustc` to a specific nightly release:
`rustup default nightly-2021-02-20`.

More info here: https://rust-lang.github.io/rustup/overrides.html