Merge pull request #11 from seek-oss/explicit-merge

Explicitly merge PRs rather than relying on GitHub refs

README.md

@@ -1,6 +1,6 @@
 # GitHub Pull Request Plugin
 
-A [Buildkite plugin](https://buildkite.com/docs/agent/v3/plugins) to build the merged state of GitHub pull requests.
+A [Buildkite plugin](https://buildkite.com/docs/agent/v3/plugins) to build the merged state of pull requests.
 
 Why would I want this?
  1. Parity with other CI setups. Including [TeamCity](https://blog.jetbrains.com/teamcity/2013/02/automatically-building-pull-requests-from-github-with-teamcity/), Travis, and [Jenkins](https://wiki.jenkins.io/display/JENKINS/GitHub+pull+request+builder+plugin).
@@ -13,7 +13,7 @@ While this approach doesn't mitigate breaking changes made to the target branch
 
 The plugin has two modes:
   - `mode: trigger` to async trigger another build (of the current pipeline); and
-  - `mode: checkout` to checkout the PR merged ref (`refs/pull/123/merge`) rather than the head (`refs/pull/123/head`)
+  - `mode: checkout` to merge the PR after checking out source
 
 # Example
 

hooks/post-checkout

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+function trigger() {
+  local pr="$1"
+  local branch="$2"
+  local slug="${BUILDKITE_PIPELINE_SLUG}"
+  echo "Triggering merged build of ${slug} for PR ${pr}"
+  cat <<EOL | buildkite-agent pipeline upload 
+  steps:
+    - label: "Merge build"
+      trigger: "${slug}"
+      async: true
+      build:
+        message: "Merge build for Pull Request ${pr}"
+        branch: "${BUILDKITE_BRANCH}"
+        env:
+          GITHUB_MERGED_PR_FORCE_BRANCH: "${2}"
+EOL
+}
+
+function merge() {
+  local target_branch="$1"
+  if [[ -z "${target_branch}" ]] ; then
+    echo "No pull request target branch"
+    exit 1
+  fi
+
+  git fetch -v origin "${target_branch}"
+  git checkout FETCH_HEAD
+  GIT_COMMITTER_NAME="github-merged-pr-buildkite-plugin" git merge "${BUILDKITE_COMMIT}"
+}
+
+force_merge="${GITHUB_MERGED_PR_FORCE_BRANCH:-}"
+if [[ -n "$force_merge" ]]; then
+  echo "Forcing merge into ${force_merge}"
+  merge "${force_merge}"
+  exit $?
+fi
+
+# this is a pull request build
+pull_request="${BUILDKITE_PULL_REQUEST:-false}"
+if [[ "${pull_request}" == "false" ]] ; then
+  echo "Not a pull request, skipping"
+  exit 0
+fi
+
+mode="${BUILDKITE_PLUGIN_GITHUB_MERGED_PR_MODE:-checkout}"
+if [[ "${mode}" == "checkout" ]]; then
+  merge "${BUILDKITE_PULL_REQUEST_BASE_BRANCH:-master}"
+  exit $?
+elif [[ "${mode}" == "trigger" ]]; then
+  trigger "${pull_request}" "${BUILDKITE_PULL_REQUEST_BASE_BRANCH:-}"
+else
+  echo "Invalid mode: ${mode}"
+  exit 1
+fi
+

tests/post-checkout.bats

@@ -0,0 +1,78 @@
+#!/usr/bin/env bats
+
+load '/usr/local/lib/bats/load.bash'
+
+post_checkout_hook="$PWD/hooks/post-checkout"
+
+@test "Triggers a build if PR number set and mode is trigger" {
+  export BUILDKITE_PULL_REQUEST=123
+  export BUILDKITE_PLUGIN_GITHUB_MERGED_PR_MODE="trigger"
+  export BUILDKITE_PIPELINE_SLUG="my-pipeline"
+  export BUILDKITE_BRANCH="dev"
+
+  stub buildkite-agent \
+    "pipeline upload : echo UPLOADED_PIPELINE"
+
+  run "$post_checkout_hook"
+
+  assert_success
+  assert_output --partial "Triggering merged build of my-pipeline for PR 123"
+  assert_output --partial "UPLOADED_PIPELINE"
+  unstub buildkite-agent
+}
+
+@test "Merges with target PR branch" {
+  export BUILDKITE_PULL_REQUEST=123
+  export BUILDKITE_PLUGIN_GITHUB_MERGED_PR_MODE="checkout"
+  export BUILDKITE_PULL_REQUEST_BASE_BRANCH="dev"
+  export BUILDKITE_COMMIT="deadbeef"
+
+  stub git \
+    "fetch -v origin dev : echo FETCHED" \
+    "checkout FETCH_HEAD : echo CHECKED_OUT" \
+    "merge deadbeef : echo MERGED"
+
+  run "$post_checkout_hook"
+
+  assert_success
+  assert_output --partial "FETCHED"
+  assert_output --partial "CHECKED_OUT"
+  assert_output --partial "MERGED"
+  unstub git
+}
+
+@test "Forces merges when GITHUB_MERGED_PR_FORCE_BRANCH is set" {
+  export BUILDKITE_COMMIT="deadbeef"
+  export GITHUB_MERGED_PR_FORCE_BRANCH="master"
+
+  stub git \
+    "fetch -v origin master : echo FETCHED" \
+    "checkout FETCH_HEAD : echo CHECKED_OUT" \
+    "merge deadbeef : echo MERGED"
+
+  run "$post_checkout_hook"
+
+  assert_success
+  assert_output --partial "FETCHED"
+  assert_output --partial "CHECKED_OUT"
+  assert_output --partial "MERGED"
+  unstub git
+}
+
+@test "Does nothing if no PR number set" {
+  export BUILDKITE_PULL_REQUEST=""
+
+  run "$post_checkout_hook"
+
+  assert_success
+  assert_output --partial "Not a pull request"
+}
+
+@test "Does nothing if PR is false" {
+  export BUILDKITE_PULL_REQUEST="false"
+
+  run "$post_checkout_hook"
+
+  assert_success
+  assert_output --partial "Not a pull request"
+}