Build PRs on CI

Closes spring-projectsgh-26882

Author: snicoll

ci/pipeline.yml

@@ -54,6 +54,11 @@ resource_types:
   source:
     repository: dpb587/github-status-resource
     tag: master
+- name: pull-request
+  type: registry-image
+  source:
+    repository: teliaoss/github-pr-resource
+    tag: v0.23.0
 - name: slack-notification
   type: registry-image
   source:
@@ -93,6 +98,14 @@ resources:
     username: ((artifactory-username))
     password: ((artifactory-password))
     build_name: ((build-name))
+- name: git-pull-request
+  type: pull-request
+  icon: source-pull
+  source:
+    access_token: ((github-ci-pull-request-token))
+    repository: ((github-repo-name))
+    base_branch: ((branch))
+    ignore_paths: ["ci/*"]
 - name: repo-status-build
   type: github-status-resource
   icon: eye-check-outline
@@ -257,6 +270,34 @@ jobs:
               <<: *slack-fail-params
     - put: repo-status-jdk15-build
       params: { state: "success", commit: "git-repo" }
+- name: build-pull-requests
+  serial: true
+  public: true
+  plan:
+    - get: ci-image
+    - get: git-repo
+      resource: git-pull-request
+      trigger: true
+      version: every
+    - do:
+      - put: git-pull-request
+        params:
+          path: git-repo
+          status: pending
+      - task: build-pr
+        image: ci-image
+        file: git-repo/ci/tasks/build-pr.yml
+        <<: *build-project-task-params
+      on_success:
+        put: git-pull-request
+        params:
+          path: git-repo
+          status: success
+      on_failure:
+        put: git-pull-request
+        params:
+          path: git-repo
+          status: failure
 - name: stage-milestone
   serial: true
   plan:
@@ -412,3 +453,5 @@ groups:
   jobs: ["stage-milestone", "stage-rc", "stage-release", "promote-milestone", "promote-rc", "promote-release", "create-github-release"]
 - name: "ci-images"
   jobs: ["build-ci-images"]
+- name: "pull-requests"
+  jobs: [ "build-pull-requests" ]

ci/tasks/build-pr.yml

@@ -0,0 +1,19 @@
+---
+platform: linux
+inputs:
+- name: git-repo
+caches:
+- path: gradle
+params:
+  BRANCH:
+  CI: true
+  GRADLE_ENTERPRISE_ACCESS_KEY:
+  GRADLE_ENTERPRISE_CACHE_USERNAME:
+  GRADLE_ENTERPRISE_CACHE_PASSWORD:
+  GRADLE_ENTERPRISE_URL: https://ge.spring.io
+run:
+  path: bash
+  args:
+    - -ec
+    - |
+      ${PWD}/git-repo/ci/scripts/build-project.sh