channel-layout.md

The Rust Release Channel Layout

NOTE This document should be considered incomplete and descriptive rather than normative. Do not rely on anything described herein to be fully correct or a definition of how things should be done.

A lot of the content herein is derived from a posting made to the Rust internals forum by Brian Anderson back in 2016.

Rust releases are deployed onto static.rust-lang.org where they are served via https. There are several parts to a release channel (stable, beta, nightly) but they all key off a manifest file and then go from there.

Channel manifests

There is a top level directory /dist/ which contains the channel manifests. The manifests are named channel-rust-[channelname].toml. Each channel manifest is accompanied by a .sha256 file which is a checksum of the manifest file and can be used to check integrity of the downloaded data. In addition each channel's manifest is also accompanied by a .asc file which is a detached GPG signature which can be used to check not only the integrity but also the authenticity of the channel manifest.

In addition to the stable, beta, and nightly channels, there is also a manifest for each release which will be called channel-rust-x.yy.z.toml with its associated .sha256 and .asc files.

To support date-based channels, there is an archive folder for each day (labelled YYYY-MM-DD) which contains copies of the requisite channel files on that day. So, for example, if you installed nightly-2019-02-16 then the channel file would be https://static.rust-lang.org/dist/2019-02-16/channel-rust-nightly.toml.

Content of channel manifests

Channel manifests are toml files. These are known as v2 manifests. The v1 manifests are simply lists of the files associated with a release and are not generated for every channel all of the time. Currently it is recommended to work only with the v2 manifests and these are the topic of this section.

The top level of the .toml file consists of two important key/value pairs. Firstly the manifest-version which is, at this time, "2", and secondly the date of the manifest (date) whose value is of the form "YYYY-MM-DD".

There are then a number of top level sections (tables) which are:

• pkg - This contains the bulk of the manifest and lists the packages which are part of the release. Typically this will be things like rust, rustc, cargo etc. The rust package is semi-special and currently is used to specify the subset of other packages which will be installed by default.

  Within packages are components and extensions. Currently components are installed by default by rustup, extensions are optional components and are available via rustup component add and friends.

• renames - This contains a set of package renames which can be used to determine the correct package to fetch when the user enters an alias for it.

  Typically renames are used when a package leaves its preview state and is considered to be release quality. For example, the actual package for rustfmt is called rustfmt-preview but since its release there has been a renames.rustfmt table whose to field is rustfmt-preview. When the user runs rustup component add rustfmt the name is automatically translated to rustfmt-preview and when the user runs rustup component list then rustfmt-preview is automatically renamed back to rustfmt for display to the user.

• profiles - This is part of the future setup for deciding the default component set to install. Instead of choosing the components of pkg.rust instead rustup will honor one of the entries in the profiles table. Usually this will be the default entry which essentially (though not exactly) boils down to ["rustc", "cargo", "rust-std", "rust-docs", "rustfmt", "clippy"].

  Other profiles include minimal (["rustc", "cargo", "rust-std"]) and complete which adds in additional things such as a copy of the standard library source (rust-src), miri, lldb, llvm-tools, and rust-analysis.

Package entries in the channel manifest

As stated above, packages list their components and extensions (mostly just the rust package) and they can provide per-target tarball and sha256 data.

For example, a package might be:

[pkg.cargo.target.powerpc64-unknown-linux-gnu]
available = true
url = "https://static.rust-lang.org/dist/2019-05-23/cargo-0.36.0-powerpc64-unknown-linux-gnu.tar.gz"
hash = "279f3a84f40e3547a8532c64643f38068accb91c21f04cd16e46579c893f5a06"
xz_url = "https://static.rust-lang.org/dist/2019-05-23/cargo-0.36.0-powerpc64-unknown-linux-gnu.tar.xz"
xz_hash = "cf93b387508f4aea4e64f8b4887d70cc07a00906b981dc0c143e92e918682e4a"

Here you can see that this is for the cargo package, and for the powerpc64-unknown-linux-gnu target. The url/hash combo is for a .tar.gz and the xz_url/xz_hash pair for the same tarball compressed with xz. Either pair of url and hash could be present, both may be present, but it is not useful for neither to be present unless available is set to false to indicate that that particular combination of package and target is unavailable in this channel at this time.

In addition, there will be a single entry providing the version for a package in the form:

[pkg.cargo]
version = "0.36.0 (6f3e9c367 2019-04-04)"

Here version will be effectively the $tool --version output, minus the tool's name.

Targets

Targets are the same triples you might use when building something with cargo build --target=$target and you can add them to your installation using rustup target add $target. When you do that, what rustup actually does is to find the rust-std package for the target in question and installs that. Essentially like an imaginary rustup component add rust-std.$target.

If a rust-std package for a target is not available = true then that target cannot be installed via rustup. This can happen for lower tier targets from time to time.

Since components and extensions are target-specific in the pkg tables, you will be able to see that rust-std for every target is specified in every rust target's extensions. This allows for cross-compilation by installation of any rust-std on any build system.