rust-releases

Introduction

The Rust programming language uses deterministic versioning for toolchain releases. Stable versions use SemVer, while nightly, beta and historical builds can be accessed by using dated builds (YY-MM-DD).

Unfortunately, a clean index of releases is not available any more. I decided to research which resources where still available and found the following solutions:

1. Use the AWS index (e.g. aws --no-sign-request s3 ls static-rust-lang-org/dist/ > dist.txt)
   • Rate-limited (only obtaining the index took ~40 seconds)
   • source
2. Build from individual release manifests
   • Requires parsing many documents
   • Approx. one week delay after a new release
   • Also has more specific toolchain information
   • Rate-limited
   • source
3. Parse Rust in-repo RELEASES.md
   • Fast
   • Stable channel only

Each of these options requires additional parsing, which is where this crate comes in: the rust-releases crate can obtain, parse and build an index from the above resources.

For each solution, the Strategy trait has been implemented, which provides a build_index method. This method returns a ReleaseIndex, which can be used to iterate over Rust releases. In addition, some implement a FetchResources trait which, through the fetch_channel method, can obtain the resources necessary to build the index of releases.

Implemented options

Technical options (eventually)

• Bring your own download tool (planned, will be a cfg option in the future)
• Optionally, use built in download tool

Applications

cargo-msrv is a tool which can be used to determine the minimal supported Rust version (MSRV). In cargo-msrv I started by parsing the latest channel manifest, and then decreasing the minor semver version.

This is not great for many reasons:

• Except for the latest released version, we are left guessing the decreased version numbers actually exist
• Only stable versions are supported, not nightly, beta, or other channels
• Only 1.x.0 versions are supported

This is not ideal, thus rust-releases was born. Now cargo-msrv can iterate over Rust releases of which we know they exist and are available.