update-rust-toolchain

You can update the pinned Rust nightly by fetching yesterday's date by default or a user-provided date, retrieving new hashes for rustc, rust-std, and clippy, and updating the sha256 entries and version comments in toolchains/BUCK.

Validating Rust nightly hashes involves retrieving the sha256 values for all components across targets, confirming their availability, updating the toolchains/BUCK file, and performing a build check to verify the toolchain's consistency.

Yes, you can specify a custom date when upgrading the Rust nightly version in Buck2. If no date is provided, the update defaults to yesterday's date to fetch the corresponding component hashes and update the configuration.

Yes, the Rust nightly toolchain update process obtains the new version string, performs a build check to confirm a successful build, and reports the before and after versions to the user to ensure the updated configuration works.

When fetching new nightly hashes for the Rust toolchain, the process covers retrieving and validating sha256 values for rustc, rust-std, and clippy across targets before preparing the toolchains/BUCK file for update.