Split the two command implementations into separate libraries (#2012)

This will allow us at the user code side to determine to include old commands, new commands or both.

wpilibOldCommands/src/main/native/include/frc/commands/ConditionalCommand.h

@@ -0,0 +1,84 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017-2019 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <wpi/Twine.h>
+
+#include "frc/commands/Command.h"
+
+namespace frc {
+
+/**
+ * A ConditionalCommand is a Command that starts one of two commands.
+ *
+ * A ConditionalCommand uses the Condition method to determine whether it should
+ * run onTrue or onFalse.
+ *
+ * A ConditionalCommand adds the proper Command to the Scheduler during
+ * Initialize() and then IsFinished() will return true once that Command has
+ * finished executing.
+ *
+ * If no Command is specified for onFalse, the occurrence of that condition
+ * will be a no-op.
+ *
+ * A ConditionalCommand will require the superset of subsystems of the onTrue
+ * and onFalse commands.
+ *
+ * @see Command
+ * @see Scheduler
+ */
+class ConditionalCommand : public Command {
+ public:
+  /**
+   * Creates a new ConditionalCommand with given onTrue and onFalse Commands.
+   *
+   * @param onTrue  The Command to execute if Condition() returns true
+   * @param onFalse The Command to execute if Condition() returns false
+   */
+  explicit ConditionalCommand(Command* onTrue, Command* onFalse = nullptr);
+
+  /**
+   * Creates a new ConditionalCommand with given onTrue and onFalse Commands.
+   *
+   * @param name    The name for this command group
+   * @param onTrue  The Command to execute if Condition() returns true
+   * @param onFalse The Command to execute if Condition() returns false
+   */
+  ConditionalCommand(const wpi::Twine& name, Command* onTrue,
+                     Command* onFalse = nullptr);
+
+  virtual ~ConditionalCommand() = default;
+
+  ConditionalCommand(ConditionalCommand&&) = default;
+  ConditionalCommand& operator=(ConditionalCommand&&) = default;
+
+ protected:
+  /**
+   * The Condition to test to determine which Command to run.
+   *
+   * @return true if m_onTrue should be run or false if m_onFalse should be run.
+   */
+  virtual bool Condition() = 0;
+
+  void _Initialize() override;
+  void _Cancel() override;
+  bool IsFinished() override;
+  void _Interrupted() override;
+
+ private:
+  // The Command to execute if Condition() returns true
+  Command* m_onTrue;
+
+  // The Command to execute if Condition() returns false
+  Command* m_onFalse;
+
+  // Stores command chosen by condition
+  Command* m_chosenCommand = nullptr;
+};
+
+}  // namespace frc