Loops with Slices

tip

We recommend reviewing Starlark Spec before attempting to create a template.

Overview

From Starlark for loops:

for i in [1, 2, 3]:
  print(i) # prints "1", "2", "3"

Sample

Let's take a look at ranging over a slice for a template:

def main(ctx):
  ruleset = {
    "event": [
      "push",
      "pull_request"
    ]
  }

  steps = [
    {
      "name": "install",
      "image": "golang:latest",
      "commands": [
        "go get ./..."
      ],
      "pull": ctx["vars"]["pull_policy"],
      "ruleset": ruleset,
    }
  ]

  for image in ctx["vars"]["images"]:
    steps.append(
      {
        "name": "test_%s" % image,
        "image": image,
        "commands": [
          "go test ./..."
        ],
        "pull": ctx["vars"]["pull_policy"],
        "ruleset": ruleset,
      }
    )

  steps.append(
    {
      "name": "build",
      "image": "golang:latest",
      "commands": [
        "go build"
      ],
      "environment": {
        "CGO_ENABLED": "0",
        "GOOS": "linux",
      },
      "pull": ctx["vars"]["pull_policy"],
      "ruleset": ruleset,
    }
  )

  pipeline = {
    'version': '1',
    'steps': steps,
  }

  return pipeline

The caller of this template could look like:

version: "1"
templates:
  - name: sample
    source: github.com/<org>/<repo>/path/to/file/<template>.star
    format: starlark
    type: github

steps:
  - name: sample
    template:
      name: golang
      vars:
        pull_policy: "always"
        images: [ golang:latest, golang:1.13, golang:1.12 ]

Which means the compiled pipeline for execution on a worker is:

version: "1"
steps:
  - name: sample_test_latest
    commands:
      - go test ./...
    image: golang:latest
    pull: always
    ruleset:
      event: [ push, pull_request ]

  - name: sample_test_golang:1.13
    commands:
      - go test ./...
    image: golang:1.13
    pull: always
    ruleset:
      event: [ push, pull_request ]

  - name: sample_test_golang:1.12
    commands:
      - go test ./...
    image: golang:1.12
    pull: always
    ruleset:
      event: [ push, pull_request ]

  - name: sample_build
    commands:
      - go build
    environment:
      CGO_ENABLED: '0'
      GOOS: linux
    image: golang:latest
    pull: always
    ruleset:
      event: [ push, pull_request ]