Scaling Rust builds with Bazel
As of March 2023, the Internet Computer repository contains about six hundred thousand lines of Rust code. Last year, we started using Bazel as our primary build system, and we couldn't have been happier with the switch. This article explains the motivation behind this move and the migration process details.
Many Rust newcomers, especially those with a C++ background, swear by cargo. Rust tooling is fantastic for beginners, but we became dissatisfied with cargo as the project size increased. Most of our complaints fall into two categories.
Cargo is the Rust package manager. Cargo downloads your Rust package's dependencies, compiles your packages, makes distributable packages, and uploads them to crates.io.
Let's acknowledge the elephant in the room: cargo is not a build system; it's a tool for building and distributing Rust packages. It can build Rust code for a specific platform with a given set of features in a single invocation. Cargo chose simplicity and ease of use over generality and scalability; it does not track dependencies well or support arbitrary build graphs.
These trade-offs make cargo easy to pick up but impose severe limitations in a complex project. There are workarounds, such as xtask, but they will only get you so far. Let's consider an example of what many of our tests must do:
