[wpilib] Add IsJoystickConnected method (#2847)

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

@@ -594,6 +594,21 @@ public class DriverStation {
     return HAL.getJoystickAxisType((byte) stick, (byte) axis);
   }
 
+  /**
+   * Returns if a joystick is connected to the Driver Station.
+   *
+   * <p>This makes a best effort guess by looking at the reported number of axis,
+   * buttons, and POVs attached.
+   *
+   * @param stick The joystick port number
+   * @return true if a joystick is connected
+   */
+  public boolean isJoystickConnected(int stick) {
+    return getStickAxisCount(stick) > 0
+      || getStickButtonCount(stick) > 0
+      || getStickPOVCount(stick) > 0;
+  }
+
   /**
    * Gets a value indicating whether the Driver Station requires the robot to be enabled.
    *

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

@@ -217,6 +217,15 @@ public abstract class GenericHID {
     return m_ds.getStickButtonCount(m_port);
   }
 
+  /**
+   * Get if the HID is connected.
+   *
+   * @return true if the HID is connected
+   */
+  public boolean isConnected() {
+    return m_ds.isJoystickConnected(m_port);
+  }
+
   /**
    * Get the type of the HID.
    *

wpilibj/src/test/java/edu/wpi/first/wpilibj/DriverStationTest.java

@@ -0,0 +1,44 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+package edu.wpi.first.wpilibj;
+
+import java.util.stream.Stream;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import edu.wpi.first.wpilibj.simulation.DriverStationSim;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
+
+class DriverStationTest {
+  @ParameterizedTest
+  @MethodSource("isConnectedProvider")
+  void testIsConnected(int axisCount, int buttonCount, int povCount, boolean expected) {
+    DriverStationSim.setJoystickAxisCount(1, axisCount);
+    DriverStationSim.setJoystickButtonCount(1, buttonCount);
+    DriverStationSim.setJoystickPOVCount(1, povCount);
+
+    DriverStationSim.notifyNewData();
+
+    assertEquals(expected, DriverStation.getInstance().isJoystickConnected(1));
+  }
+
+  static Stream<Arguments> isConnectedProvider() {
+    return Stream.of(
+      arguments(0, 0, 0, false),
+      arguments(1, 0, 0, true),
+      arguments(0, 1, 0, true),
+      arguments(0, 0, 1, true),
+      arguments(1, 1, 1, true),
+      arguments(4, 10, 1, true)
+    );
+  }
+}