layout: documentation title: Starlark Build Configurations

Starlark Build Configurations

User-definable configuration is coming to Starlark!

This makes it possible to:

define custom flags for your project, obsoleting the need for [--define][define]
[transition][transitions] deps to different configurations than their parents (e.g.--compilation_mode=opt or --cpu=arm)
bake better defaults into rules (e.g. automatically build //my:android_app with a specified SDK)

and more, all completely from .bzl files (no Bazel release required).

As of Q2'19, this effort is [partially rolled out] (https://github.com/bazelbuild/bazel/issues/5574#issuecomment-458349702) to Bazel and Bazel. Much functionality is guarded while we work out concerns about