2.8 KiB
2.8 KiB
- Cargo is not a build system. This is even in the Cargo book. But everyone treats it as such (including me).
- Cargo downloads dependencies, compiles packages, makes them distributable packages, and uploads them to crates.io.
- their tests must:
- build a sandbox binary for executing webassembly
- build a webassembly program
- post-process the webassembly program
- build and execute a test binary that launches the sandbox binary, sends the webassembly program to the sandbox, and interacts with the program
- this test flow requires three cargo commands, and thus cannot be represented as a single cargo directive
- they saw no improvement from using sscache
- they tried using Nix
- requires fine-grained derivations: each rust package must be turned into a derivation. They used cargo2nix to get there.
- developers were uncomfortable. Only the experts could modify the build rules.
- they crashed when the deployment team insisted on not using Nix.
- their builds became unbearably slow and flaky
- developers were using the nix shell, which diverged from the CI
- bazel
- easy to define and wire build targets
- adding new build rules requires expertise
- build files are verbose and boring
- gracefully handles linux and macos binaries, webassembly programs, os images, docker containers, etc, etc
- has aggressive caching
- remote caching
- distributed builds
- all tests are bazel tests, and so every developer can run any test locally
- migration took months
- built a prototype. sample repository mimicked the features.
- created a bazel rule called
cargo_build, which continued to treat Cargo as a black box. - Bazel builds binaries from Rust directly and ignores cargo.
- Added the bazel test job as soon as they possibly could
- they then started at the bottom of the stack and swapped the Cargo file out for a BUILD file one crate at a time
- they also used a visualization to show how much progress they were making
- Cargo discovers tests automatically. Bazel has to be told explicitely. They wrote a tool that compared the cargo test output and the bazel test output to ensure that all tests made it through
- remaining problems
- they've never gotten a good replacement for cargo check
- rust-analyzer support is insufficient, so they have to keep cargo files around
- there's no replacement for cargo publish yet
Bazel
I have made several attempts at using Bazel, however the rust toolchain has always failed. I have not recorded the results of the most recent failure, but it is disheartening given that Bazel is Google's tool, and Google definitely has active Rust development happening.