Restore proper use of the fork parameter

Previously, disabling forking was not possible if JVM arguments or an
agent are specified, even if the fork attribute is explicitly set to
`false`.

The  fork attribute is now detected as it should and forking is disabled
when the fork attribute is set to false, even if JVM arguments or an
agent is either specified or discovered.

Fixes gh-2220

spring-boot-tools/spring-boot-maven-plugin/src/it/run-disable-fork/pom.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>org.springframework.boot.maven.it</groupId>
+	<artifactId>run-disable-fork</artifactId>
+	<version>0.0.1.BUILD-SNAPSHOT</version>
+	<properties>
+		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+	</properties>
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>@project.groupId@</groupId>
+				<artifactId>@project.artifactId@</artifactId>
+				<version>@project.version@</version>
+				<executions>
+					<execution>
+						<phase>package</phase>
+						<goals>
+							<goal>run</goal>
+						</goals>
+						<configuration>
+							<fork>false</fork>
+							<jvmArguments>-Dfoo=bar</jvmArguments>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
+	</build>
+</project>

spring-boot-tools/spring-boot-maven-plugin/src/it/run-disable-fork/src/main/java/org/test/SampleApplication.java

+/*
+ * Copyright 2012-2014 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 org.test;
+
+public class SampleApplication {
+
+	public static void main(String[] args) {
+		String foo = System.getProperty("foo");
+		if ("bar".equals(foo)) {
+			throw new IllegalStateException("System property foo should not be available. Fork disabled");
+		}
+		System.out.println("I haz been run");
+	}
+
+}

spring-boot-tools/spring-boot-maven-plugin/src/it/run-disable-fork/verify.groovy

+import static org.junit.Assert.assertTrue
+
+def file = new File(basedir, "build.log")
+assertTrue file.text.contains("I haz been run")
+assertTrue file.text.contains("Fork mode disabled, ignoring JVM argument(s) [-Dfoo=bar]")
+

spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/RunMojo.java

@@ -135,8 +135,8 @@ public class RunMojo extends AbstractDependencyFilterMojo {
 	 * is only used if an agent or jvmArguments are specified.
 	 * @since 1.2
 	 */
-	@Parameter(property = "fork", defaultValue = "false")
-	private boolean fork;
+	@Parameter(property = "fork")
+	private Boolean fork;
 
 	@Override
 	public void execute() throws MojoExecutionException, MojoFailureException {
@@ -171,10 +171,17 @@ public class RunMojo extends AbstractDependencyFilterMojo {
 		findAgent();
 		boolean hasAgent = (this.agent != null && this.agent.length > 0);
 		boolean hasJvmArgs = (this.jvmArguments != null && this.jvmArguments.length() > 0);
-		if (this.fork || hasAgent || hasJvmArgs) {
+		boolean hasFork = this.fork != null ? this.fork : (hasAgent || hasJvmArgs);
+		if (hasFork) {
 			runWithForkedJvm(startClassName);
 		}
 		else {
+			if (hasAgent) {
+				getLog().warn("Fork mode disabled, ignoring agent");
+			}
+			if (hasJvmArgs) {
+				getLog().warn("Fork mode disabled, ignoring JVM argument(s) ["+this.jvmArguments+"]");
+			}
 			runWithMavenJvm(startClassName);
 		}
 	}

spring-boot-tools/spring-boot-maven-plugin/src/site/apt/examples/run-debug.apt.vm

@@ -6,9 +6,11 @@
  2014-05-14
  -----
 
-  The <<<run>>> goal forks a process for the boot application. It is possible to specify jvm arguments
-  to that forked process. The following configuration suspend the process until a debugger has joined
-  on port 5005
+  By default, the <<<run>>> goal runs in the same process unless jvm arguments or an agent have been specified. You
+  can enable or disable forking explicitly using the <<<fork>>> attribute.
+
+  If you need to fork the process and debug it you can add the necessary JVM arguments to enable remote debugging. The
+  following configuration suspend the process until a debugger has joined on port 5005:
 
 ---
 <project>
@@ -36,8 +38,8 @@
 </project>
 ---
 
-  These arguments can be specified on the command line as well, make sure to wrap that properly,
-  that is:
+  Note that since you specified some JVM arguments, the process is forked automatically. These arguments can be
+  specified on the command line as well, make sure to wrap that properly, that is:
 
 ---
 mvn spring-boot:run -Drun.jvmArguments="-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005"