Add JDK18 variant to CI pipeline

This commit adds a new JDK 18 variant to the CI build image and
configures a JDK18 build (sources compiled with JDK17, tests compiled
and run with JDK18) to the CI pipeline.

Closes gh-27607

ci/images/ci-image/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:focal-20210827
+FROM ubuntu:focal-20211006
 
 ADD setup.sh /setup.sh
 ADD get-jdk-url.sh /get-jdk-url.sh
@@ -6,5 +6,6 @@ RUN ./setup.sh
 
 ENV JAVA_HOME /opt/openjdk/java17
 ENV JDK17 /opt/openjdk/java17
+ENV JDK18 /opt/openjdk/java18
 
 ENV PATH $JAVA_HOME/bin:$PATH

ci/images/get-jdk-url.sh

@@ -2,10 +2,13 @@
 set -e
 
 case "$1" in
-	java17)
-		 echo "https://github.com/adoptium/temurin17-binaries/releases/download/jdk-17%2B35/OpenJDK17-jdk_x64_linux_hotspot_17_35.tar.gz"
-	;;
+  java17)
+    echo "https://github.com/adoptium/temurin17-binaries/releases/download/jdk-17%2B35/OpenJDK17-jdk_x64_linux_hotspot_17_35.tar.gz"
+  ;;
+  java18)
+    echo "https://github.com/adoptium/temurin18-binaries/releases/download/jdk-2021-10-22-05-05-beta/OpenJDK-jdk_x64_linux_hotspot_2021-10-21-23-30.tar.gz"
+  ;;
   *)
-		echo $"Unknown java version"
-		exit 1
+    echo $"Unknown java version"
+    exit 1
 esac

ci/pipeline.yml

@@ -85,6 +85,13 @@ resources:
   source:
     <<: *docker-resource-source
     repository: ((docker-hub-organization))/spring-framework-ci-jdk17
+- name: every-morning
+  type: time
+  icon: alarm
+  source:
+    start: 8:00 AM
+    stop: 9:00 AM
+    location: Europe/Vienna
 - name: artifactory-repo
   type: artifactory-resource
   icon: package-variant
@@ -109,6 +116,14 @@ resources:
     access_token: ((github-ci-status-token))
     branch: ((branch))
     context: build
+- name: repo-status-jdk18-build
+  type: github-status-resource
+  icon: eye-check-outline
+  source:
+    repository: ((github-repo-name))
+    access_token: ((github-ci-status-token))
+    branch: ((branch))
+    context: jdk18-build
 - name: slack-alert
   type: slack-notification
   icon: slack
@@ -198,6 +213,34 @@ jobs:
           "zip.type": "schema"
     get_params:
       threads: 8
+- name: jdk18-build
+  serial: true
+  public: true
+  plan:
+    - get: ci-image
+    - get: git-repo
+    - get: every-morning
+      trigger: true
+    - put: repo-status-jdk18-build
+      params: { state: "pending", commit: "git-repo" }
+    - do:
+        - task: check-project
+          image: ci-image
+          file: git-repo/ci/tasks/check-project.yml
+          privileged: true
+          timeout: ((task-timeout))
+          params:
+            TEST_TOOLCHAIN: 18
+            <<: *build-project-task-params
+      on_failure:
+        do:
+          - put: repo-status-jdk18-build
+            params: { state: "failure", commit: "git-repo" }
+          - put: slack-alert
+            params:
+              <<: *slack-fail-params
+    - put: repo-status-jdk18-build
+      params: { state: "success", commit: "git-repo" }
 - name: build-pull-requests
   serial: true
   public: true
@@ -379,7 +422,7 @@ jobs:
 
 groups:
 - name: "builds"
-  jobs: ["build"]
+  jobs: ["build", "jdk18-build"]
 - name: "releases"
   jobs: ["stage-milestone", "stage-rc", "stage-release", "promote-milestone", "promote-rc", "promote-release", "create-github-release"]
 - name: "ci-images"