Support for main class detection in installApp

I'm sure someone can do a better job of this, but here's a proposal
that works. It uses our FindMainTask to set the relevant properties
if theu are missing in the application plugin.

Fixes gh-1105

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/repackage/RepackagePluginFeatures.java

@@ -29,7 +29,7 @@ import org.springframework.boot.gradle.PluginFeatures;
  */
 public class RepackagePluginFeatures implements PluginFeatures {
 
-	private static final String REPACKAGE_TASK_NAME = "bootRepackage";
+	public static final String REPACKAGE_TASK_NAME = "bootRepackage";
 
 	@Override
 	public void apply(Project project) {

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/repackage/RepackageTask.java

@@ -55,6 +55,10 @@ public class RepackageTask extends DefaultTask {
 	public void setMainClass(String mainClass) {
 		this.mainClass = mainClass;
 	}
+	
+	public String getMainClass() {
+		return mainClass;
+	}
 
 	@TaskAction
 	public void repackage() {

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

@@ -1,9 +1,12 @@
+
 package org.springframework.boot.gradle.run;
 
 import java.io.IOException;
 
 import org.gradle.api.DefaultTask;
 import org.gradle.api.Project;
+import org.gradle.api.Task;
+import org.gradle.api.plugins.ApplicationPluginConvention;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.TaskAction;
 import org.springframework.boot.gradle.SpringBootPluginExtension;
@@ -29,28 +32,55 @@ public class FindMainClassTask extends DefaultTask {
 	private String findMainClass() {
 		Project project = getProject();
 
+		String mainClass = null;
+
 		// Try the SpringBoot extension setting
 		SpringBootPluginExtension bootExtension = project.getExtensions().getByType(
 				SpringBootPluginExtension.class);
-		if(bootExtension.getMainClass() != null) {
-			return bootExtension.getMainClass();
+		if (bootExtension.getMainClass() != null) {
+			mainClass = bootExtension.getMainClass();
 		}
 
-		// Search
-		SourceSet mainSourceSet = SourceSets.findMainSourceSet(project);
-		if (mainSourceSet == null) {
-			return null;
+		ApplicationPluginConvention application = (ApplicationPluginConvention) project.getConvention().getPlugins().get(
+				"application");
+		// Try the Application extension setting
+		if (mainClass == null && application.getMainClassName() != null) {
+			mainClass = application.getMainClassName();
 		}
-		project.getLogger().debug(
-				"Looking for main in: " + mainSourceSet.getOutput().getClassesDir());
-		try {
-			String mainClass = MainClassFinder.findSingleMainClass(mainSourceSet
-					.getOutput().getClassesDir());
-			project.getLogger().info("Computed main class: " + mainClass);
-			return mainClass;
+
+		Task runTask = getProject().getTasks().getByName("run");
+		if (mainClass == null && runTask.hasProperty("main")) {
+			mainClass = (String) runTask.property("main");
 		}
-		catch (IOException ex) {
-			throw new IllegalStateException("Cannot find main class", ex);
+
+		if (mainClass == null) {
+			// Search
+			SourceSet mainSourceSet = SourceSets.findMainSourceSet(project);
+			if (mainSourceSet != null) {
+				project.getLogger().debug(
+						"Looking for main in: "
+								+ mainSourceSet.getOutput().getClassesDir());
+				try {
+					mainClass = MainClassFinder.findSingleMainClass(mainSourceSet.getOutput().getClassesDir());
+					project.getLogger().info("Computed main class: " + mainClass);
+				} catch (IOException ex) {
+					throw new IllegalStateException("Cannot find main class", ex);
+				}
+			}
 		}
+
+		project.getLogger().info("Found main: " + mainClass);
+
+		if (bootExtension.getMainClass() == null) {
+			bootExtension.setMainClass(mainClass);
+		}
+		if (application.getMainClassName() == null) {
+			application.setMainClassName(mainClass);
+		}
+		if (!runTask.hasProperty("main")) {
+			runTask.setProperty("main", mainClass);
+		}
+
+		return mainClass;
 	}
 }

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

@@ -23,6 +23,7 @@ import org.gradle.api.Project;
 import org.gradle.api.Task;
 import org.gradle.api.plugins.JavaPluginConvention;
 import org.gradle.api.tasks.JavaExec;
+import org.gradle.api.tasks.application.CreateStartScripts;
 import org.springframework.boot.gradle.PluginFeatures;
 
 /**
@@ -47,7 +48,7 @@ public class RunPluginFeatures implements PluginFeatures {
 		project.getTasks().all(new Action<Task>() {
 			@Override
 			public void execute(Task task) {
-				if(task instanceof JavaExec) {
+				if(task instanceof JavaExec || task instanceof CreateStartScripts) {
 					task.dependsOn(FIND_MAIN_CLASS_TASK_NAME);
 				}
 			}