Reclaim docker disk space on CI during build

Attempt to fix disk space issues by removing large docker images
after they have been used.

This commit backports commits from `3.4.x` that were applied to
test the changes.

Closes gh-42776

.github/scripts/reclaim-docker-diskspace.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+echo "Reclaiming Docker Disk Space"
+echo
+
+docker image ls --format "{{.Size}} {{.ID}} {{.Repository}} {{.Tag}}" | LANG=en_US sort -rh | while read line; do
+	size=$( echo "$line" | cut -d' ' -f1 | sed -e 's/\.[0-9]*//' | sed -e 's/MB/000000/' | sed -e 's/GB/000000000/' )
+	image=$( echo "$line" | cut -d' ' -f2 )
+	repository=$( echo "$line" | cut -d' ' -f3 )
+	tag=$( echo "$line" | cut -d' ' -f4 )
+	echo "Considering $image $repository:$tag $size"
+	if [[ "$tag" =~ ^[a-f0-9]{32}$ ]]; then
+		echo "Ignoring GitHub action image $image $repository:$tag"
+	elif [[ "$tag" == "<none>" ]]; then
+		echo "Ignoring untagged image $image $repository:$tag"
+	elif [[ "$size" -lt 200000000 ]]; then
+		echo "Ignoring small image $image $repository:$tag"
+	else
+		echo "Cleaning $image $repository:$tag"
+		docker image rm $image
+	fi
+done
+
+echo "Finished cleanup, leaving the following containers:"
+echo
+docker image ls --format "{{.Size}} {{.ID}} {{.Repository}}:{{.Tag}}" | LANG=en_US sort -rh
+echo
+df -h
+echo

buildSrc/src/main/java/org/springframework/boot/build/test/DockerTestPlugin.java

@@ -18,10 +18,12 @@ package org.springframework.boot.build.test;
 
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
+import org.gradle.api.Task;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.plugins.JavaPluginExtension;
 import org.gradle.api.provider.Provider;
 import org.gradle.api.services.BuildService;
+import org.gradle.api.tasks.Exec;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.SourceSetContainer;
 import org.gradle.api.tasks.testing.Test;
@@ -43,17 +45,19 @@ public class DockerTestPlugin implements Plugin<Project> {
 	/**
 	 * Name of the {@code dockerTest} task.
 	 */
-	public static String DOCKER_TEST_TASK_NAME = "dockerTest";
+	public static final String DOCKER_TEST_TASK_NAME = "dockerTest";
 
 	/**
 	 * Name of the {@code dockerTest} source set.
 	 */
-	public static String DOCKER_TEST_SOURCE_SET_NAME = "dockerTest";
+	public static final String DOCKER_TEST_SOURCE_SET_NAME = "dockerTest";
 
 	/**
 	 * Name of the {@code dockerTest} shared service.
 	 */
-	public static String DOCKER_TEST_SERVICE_NAME = "dockerTest";
+	public static final String DOCKER_TEST_SERVICE_NAME = "dockerTest";
+
+	private static final String RECLAIM_DOCKER_SPACE_TASK_NAME = "reclaimDockerSpace";
 
 	@Override
 	public void apply(Project project) {
@@ -73,6 +77,8 @@ public class DockerTestPlugin implements Plugin<Project> {
 		});
 		project.getDependencies()
 			.add(dockerTestSourceSet.getRuntimeOnlyConfigurationName(), "org.junit.platform:junit-platform-launcher");
+		Provider<Exec> reclaimDockerSpace = createReclaimDockerSpaceTask(project, buildService);
+		project.getTasks().getByName(LifecycleBasePlugin.CHECK_TASK_NAME).dependsOn(reclaimDockerSpace);
 	}
 
 	private SourceSet createSourceSet(Project project) {
@@ -110,4 +116,28 @@ public class DockerTestPlugin implements Plugin<Project> {
 		});
 	}
 
+	private Provider<Exec> createReclaimDockerSpaceTask(Project project,
+			Provider<DockerTestBuildService> buildService) {
+		return project.getTasks().register(RECLAIM_DOCKER_SPACE_TASK_NAME, Exec.class, (task) -> {
+			task.usesService(buildService);
+			task.setGroup(LifecycleBasePlugin.VERIFICATION_GROUP);
+			task.setDescription("Reclaims Docker space on CI.");
+			task.shouldRunAfter(DOCKER_TEST_TASK_NAME);
+			task.onlyIf(this::shouldReclaimDockerSpace);
+			task.executable("bash");
+			task.args("-c",
+					project.getRootDir()
+						.toPath()
+						.resolve(".github/scripts/reclaim-docker-diskspace.sh")
+						.toAbsolutePath());
+		});
+	}
+
+	private boolean shouldReclaimDockerSpace(Task task) {
+		if (System.getProperty("os.name").startsWith("Windows")) {
+			return false;
+		}
+		return System.getenv("GITHUB_ACTIONS") != null || System.getenv("RECLAIM_DOCKER_SPACE") != null;
+	}
+
 }