bazel-skylib/README.md

Skylib

Skylib is a standard library that provides functions useful for manipulating collections, file paths, and other features that are useful when writing custom build rules in Bazel.

This library is currently under early development. Be aware that the APIs in these modules may change during this time.

Each of the .bzl files in the lib directory defines a "module"—a struct that contains a set of related functions and/or other symbols that can be loaded as a single unit, for convenience. The top-level file lib.bzl acts as an index from which the other modules can be imported.

To use the functionality here, import the modules you need from lib.bzl and access the symbols by dotting into those structs:

load("@bazel_skylib//:lib.bzl", "paths", "shell")

p = paths.basename("foo.bar")
s = shell.quote(p)

List of modules

• collections
• dicts
• paths
• selects
• sets
• shell
• unittest

Writing a new module

Steps to add a module to Skylib:

1. Create a new .bzl file in the lib directory.

2. Write the functions or other symbols (such as constants) in that file, defining them privately (prefixed by an underscore).

3. Create the exported module struct, mapping the public names of the symbols to their implementations. For example, if your module was named things and had a function named manipulate, your things.bzl file would look like this:

   def _manipulate():
     ...
   
   things = struct(
       manipulate=_manipulate,
   )
   

4. Add a line to lib.bzl to make the new module accessible from the index:

   load("@bazel_skylib//lib:things.bzl", "things")
   

5. Clients can then use the module by loading it from lib.bzl:

   load("@bazel_skylib//:lib.bzl", "things")
   
   things.manipulate()
   

6. Add unit tests for your module in the tests directory.

skylark_library

The skylark_library.bzl rule can be used to aggregate a set of Skylark files and its dependencies for use in test targets and documentation generation.