BUILD file generation

Gazelle is the tool used across the Bazel ecosystem to create and maintain BUILD files automatically.

It implements a tree walk over the source tree, essentially doing these steps:

1. List the source files, to create or update a cc_library target with those in the srcs
2. Read the source files and find the include statements.
3. Each included symbol comes from a header file. Locate the cc_library target which provides the symbol and add it to deps.
4. Merge the results with the original BUILD file

Thanks to that final step, Gazelle is non-destructive. Sections of the file which Gazelle doesn’t manage are left alone. You can also opt-out of Gazelle management of any syntactic element (a rule declaration, attribute list, or individual attribute) with a # keep comment.

Gazelle extension written in Go

Gazelle has a Language interface allowing extensions to add support for more languages. EngFlow have open-sourced an extension, which expects import statements to be relative to the repository root:

gazelle_cc

EngFlow ⋅ 8 hours ago

Gazelle extension written in Starlark

Aspect CLI includes a bridge that allows writing extensions in Starlark, Bazel’s configuration language. See https://docs.aspect.build/cli/starlark for details.

Here’s an example: Embed GitHub

Demo

We can modify source files in the bazel-examples repo and run bazel configure.