[wpilib] DriverStation: Change alliance station to use optional (#5229)

Many teams have issues trying to read the DS too early. By switching to an optional, we cause teams to check 2 things. Either 1) they explicitly check, and their code is correct, or 2) they just read .value() and their code reboots in a loop. However, because the DS will eventually connect, this 2nd case is ok, and should theoretically be undetectable on the field.

wpilibc/src/main/native/cpp/DriverStation.cpp

@@ -533,7 +533,7 @@ int DriverStation::GetReplayNumber() {
   return info.replayNumber;
 }
 
-DriverStation::Alliance DriverStation::GetAlliance() {
+std::optional<DriverStation::Alliance> DriverStation::GetAlliance() {
   int32_t status = 0;
   auto allianceStationID = HAL_GetAllianceStation(&status);
   switch (allianceStationID) {
@@ -546,11 +546,11 @@ DriverStation::Alliance DriverStation::GetAlliance() {
     case HAL_AllianceStationID_kBlue3:
       return kBlue;
     default:
-      return kInvalid;
+      return {};
   }
 }
 
-int DriverStation::GetLocation() {
+std::optional<int> DriverStation::GetLocation() {
   int32_t status = 0;
   auto allianceStationID = HAL_GetAllianceStation(&status);
   switch (allianceStationID) {
@@ -564,7 +564,7 @@ int DriverStation::GetLocation() {
     case HAL_AllianceStationID_kBlue3:
       return 3;
     default:
-      return 0;
+      return {};
   }
 }
 

wpilibc/src/main/native/include/frc/DriverStation.h

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <optional>
 #include <string>
 
 #include <units/time.h>
@@ -21,7 +22,7 @@ namespace frc {
  */
 class DriverStation final {
  public:
-  enum Alliance { kRed, kBlue, kInvalid };
+  enum Alliance { kRed, kBlue };
   enum MatchType { kNone, kPractice, kQualification, kElimination };
 
   static constexpr int kJoystickPorts = 6;
@@ -282,7 +283,7 @@ class DriverStation final {
    *
    * @return The Alliance enum (kRed, kBlue or kInvalid)
    */
-  static Alliance GetAlliance();
+  static std::optional<Alliance> GetAlliance();
 
   /**
    * Return the driver station location from the FMS.
@@ -294,7 +295,7 @@ class DriverStation final {
    *
    * @return The location of the driver station (1-3, 0 for invalid)
    */
-  static int GetLocation();
+  static std::optional<int> GetLocation();
 
   /**
    * Wait for a DS connection.