Add explicit support for Spring Cloud and Spring Boot 2

Spring Cloud does not currently work with Spring Boot 2.0.0.M4 and
later. This commit automatically downgrades to a compatible Spring Boot
version when a Spring Cloud artifact is requested.

It doesn't do that for SNAPSHOT to give a chance to Spring Cloud users
to test and validate the latest state of development.

initializr-service/src/main/java/io/spring/initializr/service/extension/SpringCloudCompatibilityRequestPostProcessor.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2012-2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.spring.initializr.service.extension;
+
+import io.spring.initializr.generator.ProjectRequest;
+import io.spring.initializr.generator.ProjectRequestPostProcessor;
+import io.spring.initializr.metadata.InitializrMetadata;
+import io.spring.initializr.util.Version;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * Temporary adapter for Spring Cloud to use a compatible Spring Boot version.
+ * 
+ * @author Stephane Nicoll
+ */
+@Component
+class SpringCloudCompatibilityRequestPostProcessor
+		implements ProjectRequestPostProcessor {
+
+	private static final Version VERSION_2_0_0_M4 = Version.parse("2.0.0.M4");
+
+	@Override
+	public void postProcessAfterResolution(ProjectRequest request, InitializrMetadata metadata) {
+		Version requestVersion = Version.safeParse(request.getBootVersion());
+		if (isIncompatibleMilestone(requestVersion) && hasSpringCloud(request)) {
+			request.setBootVersion("2.0.0.M3");
+		}
+	}
+
+	private boolean isIncompatibleMilestone(Version requestVersion) {
+		return VERSION_2_0_0_M4.compareTo(requestVersion) <= 0
+				&& "M".equals(requestVersion.getQualifier().getQualifier());
+	}
+
+	private boolean hasSpringCloud(ProjectRequest request) {
+		return request.getResolvedDependencies().stream()
+				.anyMatch(d -> d.getId().startsWith("cloud-"));
+	}
+
+}

initializr-service/src/test/java/io/spring/initializr/service/extension/SpringCloudCompatibilityRequestPostProcessorTests.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2012-2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.spring.initializr.service.extension;
+
+import io.spring.initializr.generator.ProjectRequest;
+import org.junit.Test;
+
+/**
+ * Tests for {@link SpringCloudCompatibilityRequestPostProcessor}.
+ *
+ * @author Stephane Nicoll
+ */
+public class SpringCloudCompatibilityRequestPostProcessorTests
+		extends AbstractRequestPostProcessorTests {
+
+	@Test
+	public void springBoot2MilestoneDowngradedWithSpringCloud() {
+		ProjectRequest request = createProjectRequest("cloud-config-server");
+		request.setBootVersion("2.0.0.M7");
+		generateMavenPom(request)
+				.hasSpringBootParent("2.0.0.M3");
+	}
+
+	@Test
+	public void springBoot2SnapshotWithSpringCloudUsesLatest() {
+		ProjectRequest request = createProjectRequest("cloud-config-server");
+		request.setBootVersion("2.0.0.BUILD-SNAPSHOT");
+		generateMavenPom(request)
+				.hasSpringBootParent("2.0.0.BUILD-SNAPSHOT");
+	}
+
+	@Test
+	public void springBoot2MilestoneNotDowngradedWithoutSpringCloud() {
+		ProjectRequest request = createProjectRequest("web");
+		request.setBootVersion("2.0.0.M7");
+		generateMavenPom(request)
+				.hasSpringBootParent("2.0.0.M7");
+	}
+
+	@Test
+	public void onlySpringBoot2MilestoneHandled() {
+		ProjectRequest request = createProjectRequest("cloud-config-server");
+		request.setBootVersion("2.0.0.RC1");
+		generateMavenPom(request)
+				.hasSpringBootParent("2.0.0.RC1");
+	}
+
+	@Test
+	public void onlySpringBoot2Handled() {
+		ProjectRequest request = createProjectRequest("cloud-config-server");
+		request.setBootVersion("1.5.7.RELEASE");
+		generateMavenPom(request)
+				.hasSpringBootParent("1.5.7.RELEASE");
+	}
+
+}