|0.1.0||Oct 18, 2019|
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cargo-xtask is way to add free-form automation to a Rust project, a-la
npm run or bespoke bash scripts.
The two distinguishing features of xtask are:
- It doesn't require any other binaries besides
rustc, it fully bootstraps from them
- Unlike bash, it can more easily be cross platform, as it doesn't use the shell.
cargo-xtask is neither an officially recommended workflow, nor a de-facto standard (yet?). It might or might not work for your use case.
How Does It Work?
cargo-xtask is a polyfill for cargo workflows feature.
It is a way to extend stock, stable cargo with custom commands (
xtasks), written in Rust.
This polyfill doesn't need any code, just a particular configuration of a cargo project. This repository serves as a specification of such configuration.
The best way to create an xtask is to do so inside of a Cargo workspace. If you don't have a workspace already, you can create one inside your package by moving the contents into a new directory. Let's say that our package is named "testing." We first move everything into a sub-directory:
$ mkdir testing # then move all of the stuff except your .git directory into the new testing directory: $ mv src testing $ mv Cargo.toml testing $ mv .gitignore testing $ mv README.md testing # Don't forget anything else your package may have.
Then, add a new package named
$ cargo new --bin xtask
Then, we need to create a
Cargo.toml for our workspace:
[workspace] members = [ "testing", "xtask", ]
If you had a workspace previously, you'd add
xtask to your existing workspace
Then, the alias. This is where the magic happens. Create a
$ mkdir .cargo
and create a file in it named
config with these contents:
[alias] xtask = "run --package xtask --"
Example directory layout:
/testing .git .cargo/ config Cargo.toml testing/ Cargo.toml .gitignore src/ lib.rs xtask/ Cargo.toml src/ main.rs
xtask directory and the
.cargo/config should be committed to the version control system.
If you don't want to use a workspace, you can use
run --manifest-path ./xtask/Cargo.toml -- for the alias, but this is not recommended.
xtask binary should expect at least one positional argument, which is a name of the task to be executed.
Tasks are implemented in Rust, and can use arbitrary crates from crates.io.
Tasks can execute
cargo (it is advisable to use
CARGO environmental variable to get the right
xtask crate may or may not be a part of the main workspace. Usually, but not always, the workspace setup is better.
xtask is a part of the workspace, you can share dependencies between
xtask and main crates, and dependencies update process is easier.
Additionally, you will be able to use
xtask = "run --package xtask --" as an alias, which works regardless of Cargo's working directory
xtask is not a part of the workspace, you can use different feature sets for shared dependencies, and you can cache
xtask/target more easily on CI.
It is advisable to commit
xtask lockfile to the repository.
It is advisable to minimize the compile time of xtasks.
You can find some examples of xtasks in the
./examples directory in this repository.
The current recommendation is to define various task as subcommands of the single
An alternative is to use a separate binary and a separate entry in
.cargo/config for each task.
xtasks do not integrate with Cargo lifecycle.
If you need to do custom post-processing after
cargo build, you'll need to define and call
cargo xtask build task, which calls
cargo build internally.
There's no way to intercept stock
cargo build command.
It's impossible to use xtasks from dependencies, xtasks are project-local. However, it is possible to share logic for implementing common xtasks as crates.io packages.
xtask is not a workspace member,
cargo xtask will work only from the project's root directory.
cargo xtask task-name command to run the task.
cargo xtask deploy
Note that this doesn't require any additional setup besides cloning the repository, and will automatically build the
xtask binary on the first run.
Not Using xtasks
xtasks are entirely optional, and you don't have to use them!
In particular, if, for your purposes,
cargo build and
cargo test are enough, don't use xtasks.
If you prefer to write a short bash script, and don't need to support windows, there's no need to use xtasks either.
The following specifies the names and behaviors of some common xtasks, to help establish common conventions. If you want to tweak behavior of a standard task for your project, you can add custom flags to it. If you feel an important common task is missing, feel free to submit a PR!
cargo xtask --help
When run without argument or with the
xtask should print a help message which lists available tasks.
cargo xtask dist
This should package the software and produce a set of distributable artifacts.
Artifacts should be placed into
The precise meaning of artifacts is not defined, but, for a CLI tool, you can expect the binary itself (build in release mode and stripped), man pages and shell completion files.
dist command should clean the
./target/dist directory before populating it with artifacts.
It is expected that the
dist command calls
cargo build --release internally.
See #3 for additional discussion.
cargo xtask codegen
This command should run code generation, which happens outside of
For example, if you are writing a gPRC server, and would like to commit the generated code into the repository (so that the clients don't have to have
protoc installed), you can implement code generation as
cargo xtask codegen.
cargo xtask ci
This task should run
cargo test and any additional checks that are required on CI, like checking formatting, running
miri test, checking links in the documentation.
The CI configuration should generally look like this:
script: - cargo xtask ci
The expectation is that, if
cargo xtask ci passes locally, the CI will be green as well.
You don't need this task if
cargo test is enough for your purposes.
Moreover, there are certain tradeoffs associated with using xtasks instead of CI provider's built-in ways to specify CI process.
So, we do not recommend to blindly use
xtask ci over
.travis.yml, but, if you want to use xtasks for CI, use
ci as the name of the task.
See #1 for discussion.
- devx: collection of useful utilities (spawning processes, git pre-commit hooks, etc.)
- xshell: ergonomic "bash" scripting in Rust
- duct: a library for running child processes with support for pipelines and IO redirection
If you write tools or libraries for xtasks, send a PR to this document. Some possible ideas:
- cargo subcomand to generate
- implementations of common xtasks, like "check that code is formatted with rustfmt" or "build completions for a clap app", as libraries.
To my knowledge, the idea of xtasks was first introduced in this post. In some sense, the present document just specifies some conventions around original idea.
xtask is chosen so as not to conflict with potential future built-in cargo feature for tasks.