The rustup working group is announcing the release of rustup version 1.25.1. Rustup is the recommended tool to install Rust, a programming language that is empowering everyone to build reliable and efficient software.

If you have a previous version of rustup installed, getting rustup 1.25.1 is as easy as stopping any programs which may be using Rustup (e.g. closing your IDE) and running:

rustup self update

Rustup will also automatically update itself at the end of a normal toolchain update:

rustup update

If you don't have it already, you can get rustup from the appropriate page on our website.

What's new in rustup 1.25.1

This version of rustup fixes a regression introduced in the previous release (1.25.0), which caused some workflows to fail.

Regression in nested Cargo invocations with different toolchains

When you invoke Rust or Cargo installed by rustup, you're not running them directly. Instead, you run rustup "proxy" binaries, whose job is to detect the right toolchain (parsing the +channel CLI argument or using one of the defaults) and run it.

Running these proxies is not instantaneous though, and for example a cargo build invocation might execute several of them (the initial cargo invocation plus one rustc for every dependency), slowing down the build.

To improve performance, rustup 1.25.0 changed the proxies code to set the RUSTC and RUSTDOC environment variables when missing, which instructed Cargo to skip the proxies and invoke the binaries defined in those variables directly. This provided a performance gain when building crates with lots of dependencies.

Unfortunately this change broke some users of rustup, who did something like:

• The first Cargo invocation (for example an extension, an alias or an integration test) uses toolchain foo, setting the RUSTC and RUSTDOC environment variables pointing to that toolchain.

• The first invocation calls Cargo again, but this time using toolchain bar (for example cargo +bar build). This does not set the RUSTC and RUSTDOC environment variables pointing to bar, as those variables are already present.

• The second invocation of Cargo then invokes rustc by using the RUSTC environment variable and skipping the proxy, which results in the foo toolchain being invoked. Previous versions of rustup invoked the proxy instead, which would correctly detect and use the bar toolchain.

Rustup 1.25.1 fixes this regression by reverting the change. The rustup working group is discussing in issue #3035 plans to re-introduce the change in a future release while avoiding breakage.

Thanks

Thanks again to all the contributors who made rustup 1.25.1 possible!

• Daniel Silverstone (kinnison)
• Robert Collins (rbtcollins)
• Jynn Nelson (jyn514)
• Pietro Albini (pietroalbini)