Cloudfoundry buildpack for Rust

This is a fork of https://github.com/emk/heroku-buildpack-rust, tweaked to work on cloudfoundry (or at least, our cloudfoundry deployment).

This is a Heroku buildpack for Rust with support for cargo and rustup. Features include:

• Caching of builds between deployments.
• Automatic updates to the latest stable Rust by default.
• Optional pinning of Rust to a specific version.
• Support for export so that other buildpacks can access the Rust toolchain.
• Support for compiling Rust-based extensions for projects written in other languages.

Using this buildpack

You will first need to set your buildpack in your manifest.yml:

---
applications:
- name: my-project-hello
  memory: 64M
  buildpacks:
  - https://github.com/alphagov/cf-buildpack-rust

You will also need to create a Procfile pointing to the release version of your application, and commit it to git:

web: ./target/release/hello

...where hello is the name of your binary.

Running Diesel migrations during the release phase

This will install the diesel CLI at build time and make it available in your app. Migrations will run whenever a new version of your app is released. Add the following line to your RustConfig

RUST_INSTALL_DIESEL=1

and this one to your Procfile

release: ./target/release/diesel migration run

Specifying which version of Rust to use

By default, your application will be built using the latest stable Rust. Normally, this is pretty safe: New stable Rust releases have excellent backwards compatibility.

But you may wish to use nightly Rust or to lock your Rust version to a known-good configuration for more reproducible builds. To specify a specific version of the toolchain, use a rust-toolchain file in the format rustup uses.

Note: if you previously specified a VERSION variable in RustConfig, that will continue to work, and will override a rust-toolchain file.

Customizing build flags

If you want to change the cargo build command, you can set the RUST_CARGO_BUILD_FLAGS variable inside the RustConfig file.

RUST_CARGO_BUILD_FLAGS="--release -p some_package --bin some_exe --bin some_bin_2"

The default value of RUST_CARGO_BUILD_FLAGS is --release. If the variable is not set in RustConfig, the default value will be used to build the project.

Development notes

If you need to tweak this buildpack, the following information may help.

Testing with Docker

To test changes to the buildpack using the included docker-compose-test.yml, run:

./test_buildpack

Then make sure there are no Rust-related *.so files getting linked:

ldd heroku-rust-cargo-hello/target/release/hello

This uses the Docker image heroku/cedar, which allows us to test in an official Cedar-like environment.