[commands] Enhance Command Sendable implementations (#4822)

wpilibNewCommands/src/main/native/include/frc2/command/SelectCommand.h

@@ -10,11 +10,14 @@
 #endif
 
 #include <memory>
+#include <string>
 #include <type_traits>
 #include <unordered_map>
 #include <utility>
 #include <vector>
 
+#include <wpi/sendable/SendableBuilder.h>
+
 #include "frc2/command/CommandBase.h"
 #include "frc2/command/PrintCommand.h"
 
@@ -122,6 +125,21 @@ class SelectCommand : public CommandHelper<CommandBase, SelectCommand<Key>> {
     return m_interruptBehavior;
   }
 
+  void InitSendable(wpi::SendableBuilder& builder) override {
+    CommandBase::InitSendable(builder);
+
+    builder.AddStringProperty(
+        "selected",
+        [this] {
+          if (m_selectedCommand) {
+            return m_selectedCommand->GetName();
+          } else {
+            return std::string{"null"};
+          }
+        },
+        nullptr);
+  }
+
  protected:
   std::unique_ptr<Command> TransferOwnership() && override {
     return std::make_unique<SelectCommand>(std::move(*this));