Contributing to rustup

  1. Fork it!
  2. Create your feature branch: git checkout -b my-new-feature
  3. Test it: cargo test --features=test
  4. Lint it!
  5. Commit your changes: git commit -am 'Add some feature'
  6. Push to the branch: git push origin my-new-feature
  7. Submit a pull request :D

For developing on rustup itself, you may want to install into a temporary directory, with a series of commands similar to this:

cargo build
mkdir home
RUSTUP_HOME=home CARGO_HOME=home target/debug/rustup-init --no-modify-path -y

You can then try out rustup with your changes by running home/bin/rustup, without affecting any existing installation. Remember to keep those two environment variables set when running your compiled rustup-init or the toolchains it installs, but unset when rebuilding rustup itself.

If you wish to install your new build to try out longer term in your home directory then you can run cargo dev-install which is an alias in .cargo/config which runs cargo run -- --no-modify-path -y to install your build into your homedir.

We use rustfmt to keep our codebase consistently formatted. Please ensure that you have correctly formatted your code (most editors will do this automatically when saving) or it may not pass the CI tests.

If you are moving, renaming or removing an existing mdBook page, please use mdBook’s output.html.redirect feature to ensure that the old URL gets redirected.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as in the README, without any additional terms or conditions.

Linting

We use cargo clippy to ensure high-quality code and to enforce a set of best practices for Rust programming. However, not all lints provided by cargo clippy are relevant or applicable to our project. We may choose to ignore some lints if they are unstable, experimental, or specific to our project. If you are unsure about a lint, please ask us in the rustup Discord channel.

Manual linting

When checking the codebase with clippy, it is recommended to use the following command:

$ cargo clippy --all --all-targets --all-features -- -D warnings

Please note the --all-features flag: it is used because we need to enable the test feature to make lints fully work, for which --all-features happens to be a convenient shortcut.

The test feature is required because rustup uses cargo features to conditionally compile support code for integration tests, as #[cfg(test)] is only available for unit tests.

If you encounter an issue or wish to speed up the initial analysis, you could also try activating only the test feature by replacing --all-features with --features=test.

Rust-Analyzer

When checking the codebase using rust-analyzer, the first thing to do remains unchanged: enabling the features.

This is done by setting the rust-analyzer.cargo.features property to "all".

For example, if you are using rust-analyzer within VSCode, you would want to add the following to your project’s .vscode/settings.json1:

"rust-analyzer.cargo.features": "all",
1

Alternatively, if you want to apply the configuration to all your Rust projects, you can add it to your global configuration at ~/.config/Code/User/settings.json instead.

Alternatively, if you want to enable the test feature only, you should set the following instead:

"rust-analyzer.cargo.features": ["test"]

Next, as rust-analyzer depends on cargo check by default, it is also recommended to enable the cargo clippy integration by adding the following:

"rust-analyzer.check.command": "clippy",

You might also want to refer to the rust-analyzer manual for more details on properly setting up rust-analyzer in your IDE of choice.

Coding standards

Generally we just follow good sensible Rust practices, clippy and so forth. However there are some practices we’ve agreed on that are not machine-enforced; meeting those requirements in a PR will make it easier to merge.

Atomic commits

We use atomic commits across the repo. Each commit should represent a single unit of change. You can read more about atomic commits here.

Import grouping

In each file the imports should be grouped into at most 4 groups in the following order:

  1. stdlib
  2. non-repository local crates
  3. repository local other crates
  4. this crate

Separate each group with a blank line, and rustfmt will sort into a canonical order. Any file that is not grouped like this can be rearranged whenever the file is touched - we’re not precious about having it done in a separate commit, though that is helpful.

No direct use of process state outside rustup::process

The rustup::process module abstracts the global state that is std::env::args, std::env::vars, std::io::std* and std::env::current_dir permitting threaded tests of the CLI logic; use the relevant methods of the rustup::process::Process type rather than those APIs directly. Usually, a process: &Process variable will be available to you in the current context. For example, it could be in the form of a parameter of the current function, or a field of a Cfg instance, etc.

Clippy lints

We do not enforce lint status in the checks done by GitHub Actions, because clippy is a moving target that can make it hard to merge for little benefit.

We do ask that contributors keep the clippy status clean themselves.

Minimally, run cargo clippy --all --all-targets --features test -- -D warnings before submitting code.

If possible, adding --all-features to the command is useful, but will require additional dependencies like libcurl-dev.

Regular contributors or contributors to particularly OS-specific code should also make sure that their clippy checking is done on at least Linux and Windows, as OS-conditional code is a common source of unused imports and other small lints, which can build up over time.

For developers using BSD/Linux/Mac OS, there are Windows VM’s suitable for such development tasks for use with virtualbox and other hypervisors are downloadable from Microsoft. Similarly, there are many Linux and Unix operating systems images available for developers whose usual operating system is Windows. Currently Rustup has no Mac OS specific code, so there should be no need to worry about Mac VM images.

Clippy is also run in GitHub Actions, in the General Checks / Checks build task, but not currently run per-platform, which means there is no way to find out the status of clippy per platform without running it on that platform as a developer.

Version numbers

If you ever see a released version of rustup which has :: in its version string then something went wrong with the CI and that needs to be addressed.

We use git-testament to construct our version strings. This records, as a struct, details of the git commit, tag description, and also an indication of modifications to the working tree present when the binary was compiled.

During normal development you may get information from invoking rustup --version which looks like rustup-init 1.18.3+15 (a54051502 2019-05-26) or even rustup-init 1.18.3+15 (a54051502 2019-05-26) dirty 1 modification.

The first part is always the binary name as per clap’s normal operation. The version number is a combination of the most recent tag in the git repo, and the number of commits since that tag. The parenthesised information is, naturally, the SHA of the most recent commit and the date of that commit. If the indication of a dirty tree is present, the number of changes is indicated. This combines adds, deletes, modifies, and unknown entries.

You can request further information of a rustup binary with the rustup dump-testament hidden command. It produces output of the form:

$ rustup dump-testament
Rustup version renders as: 1.18.3+15 (a54051502 2019-05-26) dirty 1 modification
Current crate version: 1.18.3
Built from branch: kinnison/version-strings
Commit info: 1.18.3+15 (a54051502 2019-05-26)
Modified: CONTRIBUTING.md

This can be handy when you are testing development versions on your PC and cannot remember exactly which version you had installed, or if you have given a development copy (or instruction to build such) to a user, and wish to have them confirm exactly what they are using.

Finally, we tell git-testament that we trust the stable branch to carry releases. If the build is being performed when not on the stable branch, and the tag and CARGO_PKG_VERSION differ, then the short version string will include both, in the form rustup-init 1.18.3 :: 1.18.2+99 (a54051502 2019-05-26) which indicates the crate version before the rest of the commit. On the other hand, if the build was on the stable branch then regardless of the tag information, providing the commit was clean, the version is always replaced by the crate version. The dump-testament hidden command can reveal the truth however.

Making a release

Before making a release, ensure that rustup-init.sh is behaving correctly, and that you’re satisfied that nothing in the ecosystem is breaking because of the update. A useful set of things to check includes verifying that real-world toolchains install okay, and that rust-analyzer isn’t broken by the release. While it’s not our responsibility if they depend on non-stable APIs, we should behave well if we can.

As a maintainer, you have two options to choose from when cutting a new release: a beta release or an official release. The main difference between the two is that they use different values for the RUSTUP_UPDATE_ROOT environment variable:

  • A beta release is deployed on https://dev-static.rust-lang.org/rustup.
  • An official release is deployed on https://static.rust-lang.org/rustup.

By switching between those two values, Rustup effectively provides two “self update channels”, making beta testing possible with rustup self update.

Producing the final release artifacts is a bit involved because of the way Rustup is distributed. Below is a list of things to be done in order to cut a new [b]eta release or an official [r]elease:

  1. [b/r] In a separate PR:
    1. If the version strings in Cargo.tomls haven’t been updated:
      • Decide what the new version number $VER_NUM should be.

        Note: We always increment the minor number unless:

        • A major incompatibility has been introduced in this release: increment the major number instead.
        • This release is a hotfix because the last one had a defect: increment the patch number instead.
      • Update Cargo.toml and download/Cargo.toml to have that same new version number, then run cargo build and review Cargo.lock changes. If all looks well, make a commit.
    2. Update CHANGELOG.md accordingly if necessary.
  2. [b/r] After merging the PR made in step 1, in a separate PR:
    1. Update the commit shasum in rustup-init.sh to match the latest commit on master.
  3. [b/r] After merging the PR made in step 2, sync master to stable using --ff-only:
    • git fetch origin master:master
    • git checkout stable && git merge --ff-only master
    • git push origin HEAD:stable
  4. [b/r] While you wait for green CI on stable, double-check the functionality of rustup-init.sh and rustup-init just in case.
  5. [b/r] Ensure all of CI is green on the stable branch. Once it is, check through a representative proportion of the builds looking for the reported version statements to ensure that we definitely built something cleanly which reports as the right version number when run --version.
  6. [r] Make a new PR to the Rust Blog adding a new release announcement post.
  7. [b/r] Ping someone in the release team to perform the actual release. They can find instructions in ci/sync-dist.py.

    Note: Some manual testing occurs here, so hopefully they’ll catch anything egregious in which case abort the change and roll back.

  8. [b] Once the beta release has happened, post a new topic named “Seeking beta testers for Rustup $VER_NUM” on the Internals Forum.
  9. [r] Once the official release has happened, prepare and push a tag on the latest stable commit.
    • git tag -as $VER_NUM -m $VER_NUM (optionally without -s if not GPG signing the tag)
    • git push origin $VER_NUM

Developer tips and tricks

RUSTUP_FORCE_ARG0

The environment variable RUSTUP_FORCE_ARG0 can be used to get rustup to think it’s a particular binary, rather than e.g. copying it, symlinking it or other tricks with exec. This is handy when testing particular code paths from cargo run.

RUSTUP_FORCE_ARG0=rustup cargo run -- uninstall nightly

RUSTUP_BACKTRACK_LIMIT

If it’s necessary to alter the backtracking limit from the default of half a release cycle for some reason, you can set the RUSTUP_BACKTRACK_LIMIT environment variable. If this is unparsable as an i32 or if it’s absent then the default of 21 days (half a cycle) is used. If it parses and is less than 1, it is clamped to 1 at minimum.

This is not meant for use by users, but can be suggested in diagnosing an issue should one arise with the backtrack limits.

RUSTUP_MAX_RETRIES

When downloading a file, rustup will retry the download a number of times. The default is 3 times, but if this variable is set to a valid usize then it is the max retry count. A value of 0 means no retries, thus the default of 3 will mean a download is tried a total of four times before failing out.

RUSTUP_BACKTRACE

By default while running tests, we unset some environment variables that will break our testing (like RUSTUP_TOOLCHAIN, SHELL, ZDOTDIR, RUST_BACKTRACE). But if you want to debug locally, you may need backtrace. RUSTUP_BACKTRACE is used like RUST_BACKTRACE to enable backtraces of failed tests.

NOTE: This is a backtrace for the test, not for any subprocess invocation of rustup process running in the test

$ RUSTUP_BACKTRACE=1 cargo test --release --test cli-v1 -- remove_toolchain_then_add_again
    Finished release [optimized] target(s) in 0.38s
     Running target\release\deps\cli_v1-1f29f824792f6dc1.exe

running 1 test
test remove_toolchain_then_add_again ... FAILED

failures:

---- remove_toolchain_then_add_again stdout ----
thread 'remove_toolchain_then_add_again' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 1142, kind: Other, message: "An attempt was made to create more links on a file than the file system supports." }', src\libcore\result.rs:999:5
stack backtrace:
   0: backtrace::backtrace::trace_unsynchronized
             at C:\Users\appveyor\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.29\src\backtrace\mod.rs:66
   1: std::sys_common::backtrace::_print
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\sys_common\backtrace.rs:47
   2: std::sys_common::backtrace::print
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\sys_common\backtrace.rs:36
   3: std::panicking::default_hook::{{closure}}
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:198
   4: std::panicking::default_hook
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:209
   5: std::panicking::rust_panic_with_hook
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:475
   6: std::panicking::continue_panic_fmt
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:382
   7: std::panicking::rust_begin_panic
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libstd\panicking.rs:309
   8: core::panicking::panic_fmt
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libcore\panicking.rs:85
   9: core::result::unwrap_failed
  10: cli_v1::mock::clitools::test
  11: alloc::boxed::{{impl}}::call_once<(),FnOnce<()>>
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\src\liballoc\boxed.rs:746
  12: panic_unwind::__rust_maybe_catch_panic
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libpanic_unwind\lib.rs:82
  13: std::panicking::try
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\src\libstd\panicking.rs:273
  14: std::panic::catch_unwind
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\src\libstd\panic.rs:388
  15: test::run_test::run_test_inner::{{closure}}
             at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libtest\lib.rs:1466
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.


failures:
    remove_toolchain_then_add_again

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 26 filtered out

error: test failed, to rerun pass '--test cli-v1'

Tracing

Similar to other tools in the Rust ecosystem like rustc and cargo, rustup also provides observability/logging features via the tracing crate.

The verbosity of logs is controlled via the RUSTUP_LOG environment variable using tracing_subscriber’s directive syntax.

Console-based tracing

A tracing_subscriber that prints log lines directly to stderr is directly available in the prebuilt version of rustup since v1.28.0.

For historical reasons, if RUSTUP_LOG is not set, this subscriber will print the log lines in a format that mimics the “legacy” stderr output in older versions of rustup:

> rustup default stable
info: using existing install for 'stable-aarch64-apple-darwin'
info: default toolchain set to 'stable-aarch64-apple-darwin'

  stable-aarch64-apple-darwin unchanged - rustc 1.79.0 (129f3b996 2024-06-10)

However, once RUSTUP_LOG is set to any value, rustup’s “custom logging mode” will be activated, and tracing_subscriber’s builtin output format will be used instead:

> RUSTUP_LOG=trace rustup default stable
2024-06-16T12:08:48.732894Z  INFO rustup::cli::common: using existing install for 'stable-aarch64-apple-darwin'
2024-06-16T12:08:48.739232Z  INFO rustup::cli::common: default toolchain set to 'stable-aarch64-apple-darwin'

  stable-aarch64-apple-darwin unchanged - rustc 1.79.0 (129f3b996 2024-06-10)

Please note that since RUSTUP_LOG=trace essentially accepts log lines from all possible sources, you might sometimes see log lines coming from rustup’s dependencies, such as hyper_util in the following example:

> RUSTUP_LOG=trace rustup update
[..]
2024-06-16T12:12:45.569428Z TRACE hyper_util::client::legacy::client: http1 handshake complete, spawning background dispatcher task
2024-06-16T12:12:45.648682Z TRACE hyper_util::client::legacy::pool: pool dropped, dropping pooled (("https", static.rust-lang.org))

   stable-aarch64-apple-darwin unchanged - rustc 1.79.0 (129f3b996 2024-06-10)
  nightly-aarch64-apple-darwin unchanged - rustc 1.81.0-nightly (3cf924b93 2024-06-15)

2024-06-16T12:12:45.693350Z  INFO rustup::cli::rustup_mode: cleaning up downloads & tmp directories

It is also possible to limit the sources of the log lines and the desired max level for each source. For example, set RUSTUP_LOG=rustup=DEBUG to receive log lines only from rustup itself with a max verbosity of DEBUG.

Opentelemetry tracing

Prerequisites: Before following the instructions in this section, protoc must be installed, which can be downloaded from GitHub or installed via a package manager.

The feature otel can be used when building rustup to turn on Opentelemetry tracing with an OLTP GRPC exporter.

This can be very useful for diagnosing performance or correctness issues in more complicated scenarios.

The normal OTLP environment variables can be used to customise its behaviour, but often the simplest thing is to just run a Jaeger docker container on the same host:

docker run -d --name jaeger   -e COLLECTOR_ZIPKIN_HOST_PORT=:9411   -e COLLECTOR_OTLP_ENABLED=true   -p 6831:6831/udp   -p 6832:6832/udp   -p 5778:5778   -p 16686:16686   -p 4317:4317   -p 4318:4318   -p 14250:14250   -p 14268:14268   -p 14269:14269   -p 9411:9411   jaegertracing/all-in-one:latest

Then build rustup-init with tracing:

cargo build --features=otel

Run the operation you want to analyze. For example, we can now run rustup show with tracing:

RUSTUP_FORCE_ARG0="rustup" ./target/debug/rustup-init show

And look in Jaeger for a trace.

Tracing can also be used in tests to get a trace of the operations taken during the test. To use this feature, build the project with --features=otel,test.

Adding instrumentation

The otel feature uses conditional compilation to only add function instrument when enabled. Instrumenting a currently uninstrumented function is mostly simply done like so:

#![allow(unused)]
fn main() {
#[tracing::instrument(level = "trace", err(level = "trace"), skip_all)]
}

skip_all is not required, but some core structs don’t implement Debug yet, and others have a lot of output in Debug : tracing adds some overheads, so keeping spans lightweight can help avoid frequency bias in the results - where parameters with large debug in frequently called functions show up as much slower than they are.

Some good general heuristics:

  • Do instrument slow blocking functions
  • Do instrument functions with many callers or that call many different things, as these tend to help figure the puzzle of what-is-happening
  • Default to not instrumenting thin shim functions (or at least, only instrument them temporarily while figuring out the shape of a problem)
  • Be way of debug build timing - release optimisations make a huge difference, though debug is a lot faster to iterate on. If something isn’t a problem in release don’t pay it too much heed in debug.