BazelCon 2024

Creating Bazel definitions which allow to build the same targets in multiple configurations at once (i.e. different target platforms) is possibly one of the most convoluted parts of any larger project. Bazel has rich and powerful tooling that supports such an approach, yet it is not yet exposed in an approachable way. Frequently, it leads to opaque macros and custom rules whose sole purpose is to apply some transitions, naming conventions, and more, all of which contributes to Build definitions that are not developer friendly and require a higher level of Bazel familiarity to work with. `rules_variant` is a new meta-ruleset (based on `with_cfg.bzl`) designed to address that particular issue. Desired variants (essentially Bazel configurations) are stored in a JSON file and any Bazel rule may decide to be “pinned” to a certain set of said variants, simply by referencing it via an additional attribute. From the developer’s perspective it is as simple as referencing additional names, if the Bazel target has to be built in an additional “flavor” (with specific settings). This talk showcases the incredible flexibility and readability that comes from the aforementioned approach.