Move Java main function from library to user code (#1148)

It is much more reliable than the old approach, as it no longer depends on a magic string
in a manifest file, and if the user changes their main class, or makes it not import from
something RobotBase, it will fail to compile instead of failing at runtime.

With requiring an importer, we should be able to automate this in the importer.

wpilibj/src/main/java/edu/wpi/first/wpilibj/RobotBase.java

@@ -10,10 +10,8 @@ package edu.wpi.first.wpilibj;
 import java.io.File;
 import java.io.IOException;
 import java.io.OutputStream;
-import java.net.URL;
 import java.nio.file.Files;
-import java.util.Enumeration;
-import java.util.jar.Manifest;
+import java.util.function.Supplier;
 
 import edu.wpi.cscore.CameraServerJNI;
 import edu.wpi.first.networktables.NetworkTableInstance;
@@ -200,7 +198,7 @@ public abstract class RobotBase implements AutoCloseable {
    */
   @SuppressWarnings({"PMD.AvoidInstantiatingObjectsInLoops", "PMD.AvoidCatchingThrowable",
                      "PMD.CyclomaticComplexity", "PMD.NPathComplexity"})
-  public static void main(String... args) {
+  public static <T extends RobotBase> void startRobot(Supplier<T> robotSupplier) {
     if (!HAL.initialize(500, 0)) {
       throw new IllegalStateException("Failed to initialize. Terminating");
     }
@@ -211,39 +209,23 @@ public abstract class RobotBase implements AutoCloseable {
 
     HAL.report(tResourceType.kResourceType_Language, tInstances.kLanguage_Java);
 
-    String robotName = "";
-    if (args.length > 0) {
-      robotName = args[0];
-    } else {
-      Enumeration<URL> resources = null;
-      try {
-        resources = Thread.currentThread()
-            .getContextClassLoader().getResources("META-INF/MANIFEST.MF");
-      } catch (IOException ex) {
-        ex.printStackTrace();
-      }
-      while (resources != null && resources.hasMoreElements()) {
-        try {
-          Manifest manifest = new Manifest(resources.nextElement().openStream());
-          robotName = manifest.getMainAttributes().getValue("Robot-Class");
-        } catch (IOException ex) {
-          ex.printStackTrace();
-        }
-      }
-    }
-
     System.out.println("********** Robot program starting **********");
 
-    RobotBase robot;
+    T robot;
     try {
-      robot = (RobotBase) Class.forName(robotName).newInstance();
+      robot = robotSupplier.get();
     } catch (Throwable throwable) {
       Throwable cause = throwable.getCause();
       if (cause != null) {
         throwable = cause;
       }
+      String robotName = "Unknown";
+      StackTraceElement[] elements = throwable.getStackTrace();
+      if (elements.length > 0) {
+        robotName = elements[0].getClassName();
+      }
       DriverStation.reportError("Unhandled exception instantiating robot " + robotName + " "
-          + throwable.toString(), throwable.getStackTrace());
+          + throwable.toString(), elements);
       DriverStation.reportWarning("Robots should not quit, but yours did!", false);
       DriverStation.reportError("Could not instantiate robot " + robotName + "!", false);
       System.exit(1);