Radar · Rust · #002 · Week 40 · Sep 28 – Oct 4, 2026

Pre‑release testing for 1.99.0

Nice to knowtooling

What changed: Instructions were given for testing the 1.99.0 pre‑release via a custom dist server.
Production impact: The source does not say.
Try it: Run the command shown in the post to update to the pre‑release and compile a small program.
Source: blog.rust-lang.org/inside-rust/2026/09/29/1.99.0-prerelease/

Understand it, then run it

Run it now

Todayrust

// Demonstrates how to run a command with a custom environment variable in Rust 1.98.1.
// This shows the same effect as the pre‑release testing instructions, but using std::process.

use std::process::Command;

fn main() {
    // Build the command: rustup update stable
    let mut cmd = Command::new("rustup");
    cmd.arg("update")
        .arg("stable")
        // Set the custom distribution server for this invocation only.
        .env("RUSTUP_DIST_SERVER", "https://dev-static.rust-lang.org");

    // Execute and capture the output.
    let output = cmd.output().expect("failed to execute rustup");

    // Print whether the command succeeded and its stdout/stderr.
    println!("status: {}", output.status);
    println!("stdout:\n{}", String::from_utf8_lossy(&output.stdout));
    println!("stderr:\n{}", String::from_utf8_lossy(&output.stderr));
}

What it printed when we ran it on Rust 1.98.1 (edition 2024)

status: exit status: 1
stdout:

stderr:
info: syncing channel updates for stable-x86_64-unknown-linux-gnu
error: could not create temp file /usr/local/rustup/tmp/s5g4jt_lebz5qk3e_file: Read-only file system (os error 30)

Run sends this program (for Solidity, the contract and its tests) to our own sandbox, where it is compiled and run once, with no network, and what it printed or the test report comes back here. Nothing is kept. Runs are counted per visitor for the day so everyone gets a turn; the details are on the legal page.

Written by gpt-oss-120b from the linked source · claims checked against the sources · human-reviewed