[wpilib] Use reflection to load main class, remove main from templates (#8627)

#8626 needs to switch to using reflection to load the robot class. Do
that with this PR so it's separate.

Also, remove the duplicated main files from the template, and instead
fixup vscode to handle this properly.

Author: ThadHouse

developerRobot/src/main/java/wpilib/robot/Main.java

@@ -15,6 +15,6 @@ private Main() {}
    * <p>If you change your main robot class, change the parameter type.
    */
   public static void main(String... args) {
-    RobotBase.startRobot(Robot::new);
+    RobotBase.startRobot(Robot.class);
   }
 }

shared/examplecheck.gradle

@@ -82,7 +82,7 @@ task checkTemplates(type: Task) {
             assert it.gradlebase != null
             assert it.commandversion != null
             if (it.gradlebase == 'java') {
-                assert it.mainclass != null
+                assert it.robotclass != null
             }
         }
     }
@@ -101,7 +101,7 @@ task checkExamples(type: Task) {
             assert it.gradlebase != null
             assert it.commandversion != null
             if (it.gradlebase == 'java') {
-                assert it.mainclass != null
+                assert it.robotclass != null
             }
         }
     }
@@ -119,7 +119,7 @@ task checkSnippets(type: Task) {
             assert it.foldername != null
             assert it.gradlebase != null
             if (it.gradlebase == 'java') {
-                assert it.mainclass != null
+                assert it.robotclass != null
             }
         }
     }

wpilibcExamples/src/main/cpp/examples/examples.json

@@ -520,7 +520,6 @@
     ],
     "foldername": "Xrptimed",
     "gradlebase": "cppxrp",
-    "mainclass": "Main",
     "commandversion": 2,
     "extravendordeps": [
       "xrp"

wpilibj/src/main/java/org/wpilib/framework/RobotBase.java

@@ -4,8 +4,8 @@
 
 package org.wpilib.framework;
 
+import java.lang.reflect.Constructor;
 import java.util.concurrent.locks.ReentrantLock;
-import java.util.function.Supplier;
 import org.wpilib.driverstation.DriverStation;
 import org.wpilib.hardware.hal.HAL;
 import org.wpilib.hardware.hal.HALUtil;
@@ -285,13 +285,39 @@ public static String getOpMode() {
   private static RobotBase m_robotCopy;
   private static boolean m_suppressExitWarning;
 
+  private static <T extends RobotBase> T constructRobot(Class<T> robotClass) throws Throwable {
+    Constructor<?>[] constructors = robotClass.getConstructors();
+    Constructor<?> defaultConstructor = null;
+    for (Constructor<?> constructor : constructors) {
+      Class<?>[] paramTypes = constructor.getParameterTypes();
+      if (paramTypes.length == 0) {
+        if (defaultConstructor != null) {
+          throw new IllegalArgumentException(
+              "Multiple default constructors found in robot class " + robotClass.getName());
+        }
+        defaultConstructor = constructor;
+      }
+    }
+
+    T robot;
+
+    if (defaultConstructor != null) {
+      robot = robotClass.cast(defaultConstructor.newInstance());
+    } else {
+      throw new IllegalArgumentException(
+          "No valid constructor found in robot class " + robotClass.getName());
+    }
+
+    return robot;
+  }
+
   /** Run the robot main loop. */
-  private static <T extends RobotBase> void runRobot(Supplier<T> robotSupplier) {
+  private static <T extends RobotBase> void runRobot(Class<T> robotClass) {
     System.out.println("********** Robot program starting **********");
 
     T robot;
     try {
-      robot = robotSupplier.get();
+      robot = constructRobot(robotClass);
     } catch (Throwable throwable) {
       Throwable cause = throwable.getCause();
       if (cause != null) {
@@ -366,10 +392,9 @@ public static void suppressExitWarning(boolean value) {
   /**
    * Starting point for the applications.
    *
-   * @param <T> Robot subclass.
-   * @param robotSupplier Function that returns an instance of the robot subclass.
+   * @param robotClass Robot subclass type.
    */
-  public static <T extends RobotBase> void startRobot(Supplier<T> robotSupplier) {
+  public static void startRobot(Class<? extends RobotBase> robotClass) {
     // Check that the MSVC runtime is valid.
     WPIUtilJNI.checkMsvcRuntime();
 
@@ -391,7 +416,7 @@ public static <T extends RobotBase> void startRobot(Supplier<T> robotSupplier) {
       Thread thread =
           new Thread(
               () -> {
-                runRobot(robotSupplier);
+                runRobot(robotClass);
                 HAL.exitMain();
               },
               "robot main");
@@ -411,7 +436,7 @@ public static <T extends RobotBase> void startRobot(Supplier<T> robotSupplier) {
         Thread.currentThread().interrupt();
       }
     } else {
-      runRobot(robotSupplier);
+      runRobot(robotClass);
     }
 
     // On RIO, this will just terminate rather than shutting down cleanly (it's a no-op in sim).

wpilibjExamples/build.gradle

@@ -177,7 +177,10 @@ model {
                             new groovy.json.JsonSlurper().parseText(exampleFile.text).each { entry ->
                                 project.tasks.create("run${entry.foldername}", JavaExec) { run ->
                                     run.group = "run examples"
-                                    run.mainClass = "org.wpilib.examples." + entry.foldername + "." + entry.mainclass
+                                    run.mainClass = "org.wpilib.Executor"
+                                    run.args = [
+                                        "org.wpilib.examples." + entry.foldername + "." + entry.robotclass
+                                    ]
                                     run.classpath = sourceSets.main.runtimeClasspath
                                     run.dependsOn it.tasks.install
                                     run.systemProperty 'java.library.path', filePath
@@ -222,7 +225,10 @@ model {
                             new groovy.json.JsonSlurper().parseText(snippetsFile.text).each { entry ->
                                 project.tasks.create("runSnippet${entry.foldername}", JavaExec) { run ->
                                     run.group = "run snippets"
-                                    run.mainClass = "org.wpilib.snippets." + entry.foldername + "." + entry.mainclass
+                                    run.mainClass = "org.wpilib.Executor"
+                                    run.args = [
+                                        "org.wpilib.snippets." + entry.foldername + "." + entry.robotclass
+                                    ]
                                     run.classpath = sourceSets.main.runtimeClasspath
                                     run.dependsOn it.tasks.install
                                     run.systemProperty 'java.library.path', filePath

wpilibjExamples/publish.gradle

@@ -11,6 +11,8 @@ def commandsZipBaseName = '_GROUP_org_wpilib_wpilibj_ID_commands_CLS'
 
 def outputsFolder = file("$project.buildDir/outputs")
 
+def mainFile = file("$projectDir/src/main/java/org/wpilib/Main.java")
+
 task javaExamplesZip(type: Zip) {
     destinationDirectory = outputsFolder
     archiveBaseName = examplesZipBaseName
@@ -19,6 +21,10 @@ task javaExamplesZip(type: Zip) {
         into '/'
     }
 
+    from(mainFile) {
+        into '/'
+    }
+
     from('src/main/java/org/wpilib/examples') {
         into 'examples'
     }
@@ -36,6 +42,10 @@ task javaTemplatesZip(type: Zip) {
         into '/'
     }
 
+    from(mainFile) {
+        into '/'
+    }
+
     from('src/main/java/org/wpilib/templates') {
         into 'templates'
     }

wpilibjExamples/src/main/java/org/wpilib/Executor.java

@@ -0,0 +1,27 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package org.wpilib;
+
+import org.wpilib.framework.RobotBase;
+
+/** This is the executor to launch template projects. */
+public final class Executor {
+  private Executor() {}
+
+  /** Main initialization function. */
+  public static void main(String... args) throws Throwable {
+    // Load the class file for the robot.
+    String packagePath = args[0];
+    ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+
+    System.out.println("Loading robot class: " + packagePath);
+
+    Class<?> robotClass = classLoader.loadClass(packagePath);
+
+    System.out.println("Starting robot: " + robotClass.getName());
+
+    RobotBase.startRobot(robotClass.asSubclass(RobotBase.class));
+  }
+}

…wpilib/examples/addressableled/Main.java …mples/src/main/java/org/wpilib/Main.javawpilibjExamples/src/main/java/org/wpilib/examples/addressableled/Main.java renamed to wpilibjExamples/src/main/java/org/wpilib/Main.java wpilibjExamples/src/main/java/org/wpilib/examples/addressableled/Main.java renamed to wpilibjExamples/src/main/java/org/wpilib/Main.java

@@ -2,7 +2,7 @@
 // Open Source Software; you can modify and/or share it under the terms of
 // the WPILib BSD license file in the root directory of this project.
 
-package org.wpilib.examples.addressableled;
+package org.wpilib;
 
 import org.wpilib.framework.RobotBase;
 
@@ -20,6 +20,6 @@ private Main() {}
    * <p>If you change your main robot class, change the parameter type.
    */
   public static void main(String... args) {
-    RobotBase.startRobot(Robot::new);
+    RobotBase.startRobot(org.wpilib.templates.timed.Robot.class);
   }
 }