> ## Documentation Index
> Fetch the complete documentation index at: https://aspect.build/llms.txt
> Use this file to discover all available pages before exploring further.

# BUILD file generation

> Generate C/C++ BUILD files in Bazel with Gazelle, scanning sources and include statements to maintain cc_library srcs and deps non-destructively.

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:

[https://github.com/EngFlow/gazelle\_cc](https://github.com/EngFlow/gazelle_cc)

## Gazelle extension written in Starlark

Aspect CLI includes a bridge that allows writing extensions in Starlark, Bazel’s configuration language. See [Extend Gazelle BUILD file generation](/docs/cli/guides/gazelle) for details.

Here’s an example: [https://github.com/aspect-build/bazel-examples/blob/main/.aspect/gazelle/rules\_cc.axl](https://github.com/aspect-build/bazel-examples/blob/main/.aspect/gazelle/rules_cc.axl)

### Demo

We can modify source files in the bazel-examples repo and regenerate BUILD files with the Aspect CLI's [`gazelle`](/docs/cli/tasks/gazelle) task: `aspect gazelle`. With the [`tools/bazel` wrapper](/docs/cli/install#keep-your-team-typing-bazel-with-the-tools/bazel-wrapper) installed you can also type `bazel gazelle`; without the CLI, run the target directly with `bazel run //tools/gazelle:gazelle`.