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Version: 2.7.x

Aspect's Bazel helpers library

Base Starlark libraries and basic Bazel rules which are useful for constructing rulesets and BUILD files.

This module depends on bazel-skylib. In theory all these utilities could be upstreamed to bazel-skylib, but the declared scope of that project is narrow and it's very difficult to get anyone's attention to review PRs there.

bazel-lib is just a part of what Aspect provides:


Installation instructions are included on each release:

To use a commit rather than a release, you can point at any SHA of the repo.

For example to use commit abc123:

  1. Replace url = "" with a GitHub-provided source archive like url = ""
  2. Replace strip_prefix = "bazel-lib-0.1.0" with strip_prefix = "bazel-lib-abc123"
  3. Update the sha256. The easiest way to do this is to comment out the line, then Bazel will print a message with the correct value.

Note that GitHub source archives don't have a strong guarantee on the sha256 stability, see

Public API

Copying files

  • copy_directory Copies directories to another package.
  • copy_file Copies files to another package.
  • copy_to_bin Copies a source file to output tree at the same workspace-relative path.
  • copy_to_directory Copies and arranges files and directories into a new directory.
  • write_source_files Write to one or more files or folders in the source tree. Stamp out tests that ensure the sources exist and are up to date.

Transforming files

  • jq A toolchain and custom rule for running jq, a tool that is "like sed for json".
  • yq A toolchain and custom rule for running yq, a "YAML, JSON and XML processor".

Manipulating paths

  • directory_path Provide a label to reference some path within a directory, via DirectoryPathInfo.
  • output_files Forwards a subset of the files (via the DefaultInfo provider) from a given target's DefaultInfo or OutputGroupInfo.

Writing rules

  • expand_make_vars Perform make variable and location substitions in strings..
  • expand_template Substitute templates with make variables, location resolves, stamp variables, and arbitrary strings.
  • paths Useful path resolution methods.
  • transitions Transition sources to a provided platform.
  • lists Functional-style helpers for working with list data structures.
  • utils Various utils for labels and globs.
  • params_file Generate encoded params file from a list of arguments.
  • repo_utils Useful methods for repository rule implementations.
  • run_binary Like skylib's run_binary but adds directory output support.
  • stamping Support version stamping in custom rules.
  • base64 Starlark Base64 encoder & decoder.


Generating documentation

  • docs Rules for generating docs and stamping tests to ensure they are up to date.