Ignore non-JavaExec run task when finding application's main class

Previously, FindMainClassTask would look for a property named main
on any class named run. This was based on the assumption that the
run task would be a JavaExec task (typically provided by the
application plugin). If the run task was not a JavaExec task (more
accurately, if it did not have a main property) this would result in
a build failure due to trying to read a non-existent property.

This commit updates FindMainClassTask to only use the main property
of the run task if the task is a JavaExec task. This guarantees that
the property will exist on the task, and unlike using any property
named main on a task named run, also guarantee that its value will
refer to a Java class with a main method.

Closes gh-5501

spring-boot-integration-tests/spring-boot-gradle-tests/src/test/java/org/springframework/boot/gradle/MainClassTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -18,30 +18,57 @@ package org.springframework.boot.gradle;
 
 import java.io.IOException;
 
+import org.gradle.tooling.BuildException;
 import org.gradle.tooling.ProjectConnection;
 import org.junit.BeforeClass;
 import org.junit.Test;
 
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.assertThat;
+
 /**
  * Tests for configuring a project's main class
  *
  * @author Dave Syer
+ * @author Andy Wilkinson
  */
 public class MainClassTests {
 
-	private static ProjectConnection project;
-
 	private static final String BOOT_VERSION = Versions.getBootVersion();
 
+	private static ProjectConnection project;
+
 	@BeforeClass
 	public static void createProject() throws IOException {
-		project = new ProjectCreator().createProject("main-in-boot-run");
+		project = new ProjectCreator().createProject("main-class");
 	}
 
 	@Test
 	public void mainFromBootRun() {
 		project.newBuild().forTasks("build")
-				.withArguments("-PbootVersion=" + BOOT_VERSION, "--info").run();
+				.withArguments("-PbootVersion=" + BOOT_VERSION, "-PbootRunMain=true")
+				.run();
+	}
+
+	@Test
+	public void nonJavaExecRunTaskIsIgnored() {
+		try {
+			project.newBuild().forTasks("build").withArguments(
+					"-PbootVersion=" + BOOT_VERSION, "-PnonJavaExecRun=true").run();
+		}
+		catch (BuildException ex) {
+			Throwable rootCause = getRootCause(ex);
+			assertThat(rootCause.getMessage(), is(equalTo("Unable to find main class")));
+		}
+	}
+
+	private Throwable getRootCause(Throwable ex) {
+		Throwable candidate = ex;
+		while (candidate.getCause() != null) {
+			candidate = candidate.getCause();
+		}
+		return candidate;
 	}
 
 }

spring-boot-integration-tests/spring-boot-gradle-tests/src/test/resources/main-class.gradle

@@ -14,10 +14,17 @@ apply plugin: 'spring-boot'
 group = 'installer'
 version = '0.0.0'
 
-bootRun {
+if (project.hasProperty('bootRunMain')) {
+	bootRun {
   		main = 'org.springframework.boot.SpringApplication'
+	}
+}
+
+if (project.hasProperty('nonJavaExecRun')) {
+	task run { }
 }
 
+
 jar {
 	baseName =  'installer'
 }

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/run/FindMainClassTask.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -24,6 +24,7 @@ import org.gradle.api.Task;
 import org.gradle.api.plugins.ApplicationPluginConvention;
 import org.gradle.api.plugins.ExtraPropertiesExtension;
 import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.JavaExec;
 import org.gradle.api.tasks.SourceSetOutput;
 import org.gradle.api.tasks.TaskAction;
 
@@ -85,9 +86,9 @@ public class FindMainClassTask extends DefaultTask {
 			mainClass = application.getMainClassName();
 		}
 
-		Task runTask = project.getTasks().findByName("run");
+		JavaExec runTask = findRunTask(project);
 		if (mainClass == null && runTask != null) {
-			mainClass = (String) runTask.property("main");
+			mainClass = runTask.getMain();
 		}
 
 		if (mainClass == null) {
@@ -122,9 +123,17 @@ public class FindMainClassTask extends DefaultTask {
 			application.setMainClassName(mainClass);
 		}
 		if (runTask != null && !runTask.hasProperty("main")) {
-			runTask.setProperty("main", mainClass);
+			runTask.setMain(mainClass);
 		}
 
 		return mainClass;
 	}
+
+	private JavaExec findRunTask(Project project) {
+		Task runTask = project.getTasks().findByName("run");
+		if (runTask instanceof JavaExec) {
+			return (JavaExec) runTask;
+		}
+		return null;
+	}
 }