Starlark is a dialect of Python intended for use as a configuration language. The language is developed by Google for the Bazel build tool.

Today we are pleased to announce support for Starlark scripting as an alternative to configuring your continuous integration pipelines with YAML. Complex pipelines can be difficult to create and maintain and YAML files can become unwieldy. Starlark brings the full power of a scripting language to help teams create complex pipelines with less hassle.

Example Pipeline using Starlark:

def main(ctx):
  return {
    "kind": "pipeline",
    "name": "build",
    "steps": [
      {
        "name": "build"
        "image": "alpine"
        "commands": [
            "echo hello world"
        ]
      }
    ]
  }

Starlark scripts can use functions to create complex pipelines while reducing repetition and boilerplate. This is especially useful to projects that test multiple operating systems, architectures or software versions:

def main(ctx):
  reutrn [
    pipeline("1.13"),
    pipeline("1.12"),
    pipeline("1.11"),
  ]

def pipeline(version):
  return {
    "kind": "pipeline",
    "name": "go-%s" % version,
    "steps": [
      {
        "name": "build",
        "image": "golang:%s" % version,
        "commands": [
          "go build",
          "go test -v",
        ]
      }
    ]
  }

Starlark scripts can also use repository and build details in if statements to dynamically create pipelines:

def main(ctx):
  pipeline = {
    "kind": "pipeline",
    "name": "default",
    "steps": {
      [
        "name: "test",
        "image": "node",
        "commands": [
          "npm install",
          "npm test",
        ]
      ]
    }
  }

  if (ctx.build.source.startswith("feature/") and
      ctx.build.event == "pull_request"):

    pipeline.steps.append({
      "name: "integration",
      "image": "node",
      "commands": [
        "npm run integration",
      ]
    })

  return pipeline

Try It Today

If you would like to try out Starlark scripting please download and install the Starlark extension. If you need any help, or if you have any feedback or suggestions for improvement please let us know.

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