[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.
2026-06-19 00:41:43 +00:00 · 2023-07-22 15:19:28 -07:00
parent ef155438bd
commit fc56f8049a
17 changed files with 179 additions and 86 deletions
--- a/hal/src/main/java/edu/wpi/first/hal/AllianceStationID.java
+++ b/hal/src/main/java/edu/wpi/first/hal/AllianceStationID.java
@@ -5,6 +5,7 @@
 package edu.wpi.first.hal;

 public enum AllianceStationID {
+  Unknown,
  Red1,
  Red2,
  Red3,
--- a/hal/src/main/java/edu/wpi/first/hal/DriverStationJNI.java
+++ b/hal/src/main/java/edu/wpi/first/hal/DriverStationJNI.java
@@ -147,12 +147,13 @@ public class DriverStationJNI extends JNIWrapper {
   */
  private static native int nativeGetAllianceStation();

-  public static final int kRed1AllianceStation = 0;
-  public static final int kRed2AllianceStation = 1;
-  public static final int kRed3AllianceStation = 2;
-  public static final int kBlue1AllianceStation = 3;
-  public static final int kBlue2AllianceStation = 4;
-  public static final int kBlue3AllianceStation = 5;
+  public static final int kUnknownAllianceStation = 0;
+  public static final int kRed1AllianceStation = 1;
+  public static final int kRed2AllianceStation = 2;
+  public static final int kRed3AllianceStation = 3;
+  public static final int kBlue1AllianceStation = 4;
+  public static final int kBlue2AllianceStation = 5;
+  public static final int kBlue3AllianceStation = 6;

  /**
   * Gets the current alliance station ID.
@@ -162,6 +163,8 @@ public class DriverStationJNI extends JNIWrapper {
   */
  public static AllianceStationID getAllianceStation() {
    switch (nativeGetAllianceStation()) {
+      case kUnknownAllianceStation:
+        return AllianceStationID.Unknown;
      case kRed1AllianceStation:
        return AllianceStationID.Red1;
      case kRed2AllianceStation:
--- a/hal/src/main/native/cpp/jni/DriverStationJNI.cpp
+++ b/hal/src/main/native/cpp/jni/DriverStationJNI.cpp
@@ -15,7 +15,27 @@
 #include "hal/FRCUsageReporting.h"
 #include "hal/HALBase.h"

-// TODO Static asserts
+static_assert(edu_wpi_first_hal_DriverStationJNI_kUnknownAllianceStation ==
+              HAL_AllianceStationID_kUnknown);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kRed1AllianceStation ==
+              HAL_AllianceStationID_kRed1);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kRed2AllianceStation ==
+              HAL_AllianceStationID_kRed2);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kRed3AllianceStation ==
+              HAL_AllianceStationID_kRed3);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kBlue1AllianceStation ==
+              HAL_AllianceStationID_kBlue1);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kBlue2AllianceStation ==
+              HAL_AllianceStationID_kBlue2);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kBlue3AllianceStation ==
+              HAL_AllianceStationID_kBlue3);
+
+static_assert(edu_wpi_first_hal_DriverStationJNI_kMaxJoystickAxes ==
+              HAL_kMaxJoystickAxes);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kMaxJoystickPOVs ==
+              HAL_kMaxJoystickPOVs);
+static_assert(edu_wpi_first_hal_DriverStationJNI_kMaxJoysticks ==
+              HAL_kMaxJoysticks);

 using namespace hal;
 using namespace wpi::java;
--- a/hal/src/main/native/include/hal/DriverStationTypes.h
+++ b/hal/src/main/native/include/hal/DriverStationTypes.h
@@ -42,6 +42,7 @@ typedef struct HAL_ControlWord HAL_ControlWord;

 // clang-format off
 HAL_ENUM(HAL_AllianceStationID) {
+  HAL_AllianceStationID_kUnknown = 0,
  HAL_AllianceStationID_kRed1,
  HAL_AllianceStationID_kRed2,
  HAL_AllianceStationID_kRed3,
@@ -51,7 +52,7 @@ HAL_ENUM(HAL_AllianceStationID) {
 };

 HAL_ENUM(HAL_MatchType) {
-  HAL_kMatchType_none,
+  HAL_kMatchType_none = 0,
  HAL_kMatchType_practice,
  HAL_kMatchType_qualification,
  HAL_kMatchType_elimination,
--- a/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DriverStation.cpp
+++ b/simulation/halsim_ws_core/src/main/native/cpp/WSProvider_DriverStation.cpp
@@ -84,6 +84,9 @@ void HALSimWSProviderDriverStation::RegisterCallbacks() {
          case HAL_AllianceStationID_kBlue3:
            station = "blue3";
            break;
+          case HAL_AllianceStationID_kUnknown:
+            station = "unknown";
+            break;
        }
        static_cast<HALSimWSProviderDriverStation*>(param)->ProcessHalCallback(
            {{">station", station}});
--- a/wpilibc/src/main/native/cpp/DriverStation.cpp
+++ b/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 {};
  }
 }

--- a/wpilibc/src/main/native/include/frc/DriverStation.h
+++ b/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.
--- a/wpilibc/src/test/native/cpp/simulation/DriverStationSimTest.cpp
+++ b/wpilibc/src/test/native/cpp/simulation/DriverStationSimTest.cpp
@@ -129,6 +129,17 @@ TEST(DriverStationTest, AllianceStationId) {

  auto cb = DriverStationSim::RegisterAllianceStationIdCallback(
      callback.GetCallback(), false);
+
+  // Unknown
+  allianceStation = HAL_AllianceStationID_kUnknown;
+  DriverStationSim::SetAllianceStationId(allianceStation);
+  frc::sim::DriverStationSim::NotifyNewData();
+  EXPECT_EQ(allianceStation, DriverStationSim::GetAllianceStationId());
+  EXPECT_FALSE(DriverStation::GetAlliance().has_value());
+  EXPECT_FALSE(DriverStation::GetLocation().has_value());
+  EXPECT_TRUE(callback.WasTriggered());
+  EXPECT_EQ(allianceStation, callback.GetLastValue());
+
  // B1
  allianceStation = HAL_AllianceStationID_kBlue1;
  DriverStationSim::SetAllianceStationId(allianceStation);
--- a/wpilibcExamples/src/main/cpp/examples/I2CCommunication/cpp/Robot.cpp
+++ b/wpilibcExamples/src/main/cpp/examples/I2CCommunication/cpp/Robot.cpp
@@ -18,14 +18,18 @@ void Robot::RobotPeriodic() {
  //
  // For example, "RET043" would indicate that the robot is on the red
  // alliance, enabled in teleop mode, with 43 seconds left in the match.
-  auto string = fmt::format(
-      "{}{}{}{:03}",
-      frc::DriverStation::GetAlliance() == frc::DriverStation::Alliance::kRed
-          ? "R"
-          : "B",
-      frc::DriverStation::IsEnabled() ? "E" : "D",
-      frc::DriverStation::IsAutonomous() ? "A" : "T",
-      static_cast<int>(frc::Timer::GetMatchTime().value()));
+
+  std::string allianceString = "U";
+  auto alliance = frc::DriverStation::GetAlliance();
+  if (alliance.has_value()) {
+    allianceString = alliance == frc::DriverStation::Alliance::kRed ? "R" : "B";
+  }
+
+  auto string =
+      fmt::format("{}{}{}{:03}", allianceString,
+                  frc::DriverStation::IsEnabled() ? "E" : "D",
+                  frc::DriverStation::IsAutonomous() ? "A" : "T",
+                  static_cast<int>(frc::Timer::GetMatchTime().value()));

  arduino.WriteBulk(reinterpret_cast<uint8_t*>(string.data()), string.size());
 }
--- a/wpilibcExamples/src/test/cpp/examples/DigitalCommunication/cpp/DigitalCommunicationTest.cpp
+++ b/wpilibcExamples/src/test/cpp/examples/DigitalCommunication/cpp/DigitalCommunicationTest.cpp
@@ -60,6 +60,7 @@ TEST_P(AllianceTest, Alliance) {
    case HAL_AllianceStationID_kBlue1:
    case HAL_AllianceStationID_kBlue2:
    case HAL_AllianceStationID_kBlue3:
+    case HAL_AllianceStationID_kUnknown:
      isRed = false;
      break;
    case HAL_AllianceStationID_kRed1:
@@ -76,7 +77,8 @@ INSTANTIATE_TEST_SUITE_P(
    testing::Values<HAL_AllianceStationID>(
        HAL_AllianceStationID_kRed1, HAL_AllianceStationID_kRed2,
        HAL_AllianceStationID_kRed3, HAL_AllianceStationID_kBlue1,
-        HAL_AllianceStationID_kBlue2, HAL_AllianceStationID_kBlue3),
+        HAL_AllianceStationID_kBlue2, HAL_AllianceStationID_kBlue3,
+        HAL_AllianceStationID_kUnknown),
    [](const testing::TestParamInfo<AllianceTest::ParamType>& info) {
      switch (info.param) {
        case HAL_AllianceStationID_kBlue1:
@@ -91,6 +93,8 @@ INSTANTIATE_TEST_SUITE_P(
          return std::string{"Red2"};
        case HAL_AllianceStationID_kRed3:
          return std::string{"Red3"};
+        case HAL_AllianceStationID_kUnknown:
+          return std::string{"Unknown"};
      }
      return std::string{"Error"};
    });
--- a/wpilibcExamples/src/test/cpp/examples/I2CCommunication/cpp/I2CCommunicationTest.cpp
+++ b/wpilibcExamples/src/test/cpp/examples/I2CCommunication/cpp/I2CCommunicationTest.cpp
@@ -74,6 +74,9 @@ TEST_P(AllianceTest, Alliance) {
    case HAL_AllianceStationID_kRed3:
      expected = 'R';
      break;
+    case HAL_AllianceStationID_kUnknown:
+      expected = 'U';
+      break;
  }
  EXPECT_EQ(expected, gString.at(0));
 }
@@ -83,7 +86,8 @@ INSTANTIATE_TEST_SUITE_P(
    testing::Values<HAL_AllianceStationID>(
        HAL_AllianceStationID_kRed1, HAL_AllianceStationID_kRed2,
        HAL_AllianceStationID_kRed3, HAL_AllianceStationID_kBlue1,
-        HAL_AllianceStationID_kBlue2, HAL_AllianceStationID_kBlue3),
+        HAL_AllianceStationID_kBlue2, HAL_AllianceStationID_kBlue3,
+        HAL_AllianceStationID_kUnknown),
    [](const testing::TestParamInfo<AllianceTest::ParamType>& info) {
      switch (info.param) {
        case HAL_AllianceStationID_kBlue1:
@@ -98,6 +102,8 @@ INSTANTIATE_TEST_SUITE_P(
          return std::string{"Red2"};
        case HAL_AllianceStationID_kRed3:
          return std::string{"Red3"};
+        case HAL_AllianceStationID_kUnknown:
+          return std::string{"Unknown"};
      }
      return std::string{"Error"};
    });
--- a/wpilibj/src/main/java/edu/wpi/first/wpilibj/DriverStation.java
+++ b/wpilibj/src/main/java/edu/wpi/first/wpilibj/DriverStation.java
@@ -22,6 +22,9 @@ import edu.wpi.first.util.datalog.DataLog;
 import edu.wpi.first.util.datalog.FloatArrayLogEntry;
 import edu.wpi.first.util.datalog.IntegerArrayLogEntry;
 import java.nio.ByteBuffer;
+import java.util.Map;
+import java.util.Optional;
+import java.util.OptionalInt;
 import java.util.concurrent.locks.ReentrantLock;

 /** Provide access to the network communication data to / from the Driver Station. */
@@ -67,8 +70,7 @@ public final class DriverStation {
  /** The robot alliance that the robot is a part of. */
  public enum Alliance {
    Red,
-    Blue,
-    Invalid
+    Blue
  }

  public enum MatchType {
@@ -1086,6 +1088,26 @@ public final class DriverStation {
    }
  }

+  private static Map<AllianceStationID, Optional<Alliance>> m_allianceMap =
+      Map.of(
+          AllianceStationID.Unknown, Optional.empty(),
+          AllianceStationID.Red1, Optional.of(Alliance.Red),
+          AllianceStationID.Red2, Optional.of(Alliance.Red),
+          AllianceStationID.Red3, Optional.of(Alliance.Red),
+          AllianceStationID.Blue1, Optional.of(Alliance.Blue),
+          AllianceStationID.Blue2, Optional.of(Alliance.Blue),
+          AllianceStationID.Blue3, Optional.of(Alliance.Blue));
+
+  private static Map<AllianceStationID, OptionalInt> m_stationMap =
+      Map.of(
+          AllianceStationID.Unknown, OptionalInt.empty(),
+          AllianceStationID.Red1, OptionalInt.of(1),
+          AllianceStationID.Red2, OptionalInt.of(2),
+          AllianceStationID.Red3, OptionalInt.of(3),
+          AllianceStationID.Blue1, OptionalInt.of(1),
+          AllianceStationID.Blue2, OptionalInt.of(2),
+          AllianceStationID.Blue3, OptionalInt.of(3));
+
  /**
   * Get the current alliance from the FMS.
   *
@@ -1093,26 +1115,13 @@ public final class DriverStation {
   *
   * @return the current alliance
   */
-  public static Alliance getAlliance() {
+  public static Optional<Alliance> getAlliance() {
    AllianceStationID allianceStationID = DriverStationJNI.getAllianceStation();
    if (allianceStationID == null) {
-      return Alliance.Invalid;
+      allianceStationID = AllianceStationID.Unknown;
    }

-    switch (allianceStationID) {
-      case Red1:
-      case Red2:
-      case Red3:
-        return Alliance.Red;
-
-      case Blue1:
-      case Blue2:
-      case Blue3:
-        return Alliance.Blue;
-
-      default:
-        return Alliance.Invalid;
-    }
+    return m_allianceMap.get(allianceStationID);
  }

  /**
@@ -1122,27 +1131,25 @@ public final class DriverStation {
   *
   * @return the location of the team's driver station controls: 1, 2, or 3
   */
-  public static int getLocation() {
+  public static OptionalInt getLocation() {
    AllianceStationID allianceStationID = DriverStationJNI.getAllianceStation();
    if (allianceStationID == null) {
-      return 0;
+      allianceStationID = AllianceStationID.Unknown;
    }
-    switch (allianceStationID) {
-      case Red1:
-      case Blue1:
-        return 1;

-      case Red2:
-      case Blue2:
-        return 2;
+    return m_stationMap.get(allianceStationID);
+  }

-      case Blue3:
-      case Red3:
-        return 3;
-
-      default:
-        return 0;
-    }
+  /**
+   * Gets the raw alliance station of the teams driver station.
+   *
+   * <p>This returns the raw low level value. Prefer getLocation or getAlliance unless necessary for
+   * performance.
+   *
+   * @return The raw alliance station id.
+   */
+  public static AllianceStationID getRawAllianceStation() {
+    return DriverStationJNI.getAllianceStation();
  }

  /**
--- a/wpilibj/src/main/java/edu/wpi/first/wpilibj/simulation/DriverStationSim.java
+++ b/wpilibj/src/main/java/edu/wpi/first/wpilibj/simulation/DriverStationSim.java
@@ -229,20 +229,22 @@ public final class DriverStationSim {
   */
  public static AllianceStationID getAllianceStationId() {
    switch (DriverStationDataJNI.getAllianceStationId()) {
-      case 0:
+      case DriverStationJNI.kUnknownAllianceStation:
+        return AllianceStationID.Unknown;
+      case DriverStationJNI.kRed1AllianceStation:
        return AllianceStationID.Red1;
-      case 1:
+      case DriverStationJNI.kRed2AllianceStation:
        return AllianceStationID.Red2;
-      case 2:
+      case DriverStationJNI.kRed3AllianceStation:
        return AllianceStationID.Red3;
-      case 3:
+      case DriverStationJNI.kBlue1AllianceStation:
        return AllianceStationID.Blue1;
-      case 4:
+      case DriverStationJNI.kBlue2AllianceStation:
        return AllianceStationID.Blue2;
-      case 5:
+      case DriverStationJNI.kBlue3AllianceStation:
        return AllianceStationID.Blue3;
      default:
-        return null;
+        return AllianceStationID.Unknown;
    }
  }

@@ -254,23 +256,26 @@ public final class DriverStationSim {
  public static void setAllianceStationId(AllianceStationID allianceStationId) {
    int allianceStation;
    switch (allianceStationId) {
+      case Unknown:
+        allianceStation = DriverStationJNI.kUnknownAllianceStation;
+        break;
      case Red1:
-        allianceStation = 0;
+        allianceStation = DriverStationJNI.kRed1AllianceStation;
        break;
      case Red2:
-        allianceStation = 1;
+        allianceStation = DriverStationJNI.kRed2AllianceStation;
        break;
      case Red3:
-        allianceStation = 2;
+        allianceStation = DriverStationJNI.kRed3AllianceStation;
        break;
      case Blue1:
-        allianceStation = 3;
+        allianceStation = DriverStationJNI.kBlue1AllianceStation;
        break;
      case Blue2:
-        allianceStation = 4;
+        allianceStation = DriverStationJNI.kBlue2AllianceStation;
        break;
      case Blue3:
-        allianceStation = 5;
+        allianceStation = DriverStationJNI.kBlue3AllianceStation;
        break;
      default:
        return;
--- a/wpilibj/src/test/java/edu/wpi/first/wpilibj/simulation/DriverStationSimTest.java
+++ b/wpilibj/src/test/java/edu/wpi/first/wpilibj/simulation/DriverStationSimTest.java
@@ -134,13 +134,23 @@ class DriverStationSimTest {
    DriverStationSim.setAllianceStationId(allianceStation);

    try (CallbackStore cb = DriverStationSim.registerAllianceStationIdCallback(callback, false)) {
+      // Unknown
+      allianceStation = AllianceStationID.Unknown;
+      DriverStationSim.setAllianceStationId(allianceStation);
+      DriverStationSim.notifyNewData();
+      assertEquals(allianceStation, DriverStationSim.getAllianceStationId());
+      assertFalse(DriverStation.getAlliance().isPresent());
+      assertFalse(DriverStation.getLocation().isPresent());
+      assertTrue(callback.wasTriggered());
+      assertEquals(allianceStation.ordinal(), callback.getSetValue());
+
      // B1
      allianceStation = AllianceStationID.Blue1;
      DriverStationSim.setAllianceStationId(allianceStation);
      DriverStationSim.notifyNewData();
      assertEquals(allianceStation, DriverStationSim.getAllianceStationId());
-      assertEquals(DriverStation.Alliance.Blue, DriverStation.getAlliance());
-      assertEquals(1, DriverStation.getLocation());
+      assertEquals(DriverStation.Alliance.Blue, DriverStation.getAlliance().get());
+      assertEquals(1, DriverStation.getLocation().getAsInt());
      assertTrue(callback.wasTriggered());
      assertEquals(allianceStation.ordinal(), callback.getSetValue());

@@ -149,8 +159,8 @@ class DriverStationSimTest {
      DriverStationSim.setAllianceStationId(allianceStation);
      DriverStationSim.notifyNewData();
      assertEquals(allianceStation, DriverStationSim.getAllianceStationId());
-      assertEquals(DriverStation.Alliance.Blue, DriverStation.getAlliance());
-      assertEquals(2, DriverStation.getLocation());
+      assertEquals(DriverStation.Alliance.Blue, DriverStation.getAlliance().get());
+      assertEquals(2, DriverStation.getLocation().getAsInt());
      assertTrue(callback.wasTriggered());
      assertEquals(allianceStation.ordinal(), callback.getSetValue());

@@ -159,8 +169,8 @@ class DriverStationSimTest {
      DriverStationSim.setAllianceStationId(allianceStation);
      DriverStationSim.notifyNewData();
      assertEquals(allianceStation, DriverStationSim.getAllianceStationId());
-      assertEquals(DriverStation.Alliance.Blue, DriverStation.getAlliance());
-      assertEquals(3, DriverStation.getLocation());
+      assertEquals(DriverStation.Alliance.Blue, DriverStation.getAlliance().get());
+      assertEquals(3, DriverStation.getLocation().getAsInt());
      assertTrue(callback.wasTriggered());
      assertEquals(allianceStation.ordinal(), callback.getSetValue());

@@ -169,8 +179,8 @@ class DriverStationSimTest {
      DriverStationSim.setAllianceStationId(allianceStation);
      DriverStationSim.notifyNewData();
      assertEquals(allianceStation, DriverStationSim.getAllianceStationId());
-      assertEquals(DriverStation.Alliance.Red, DriverStation.getAlliance());
-      assertEquals(1, DriverStation.getLocation());
+      assertEquals(DriverStation.Alliance.Red, DriverStation.getAlliance().get());
+      assertEquals(1, DriverStation.getLocation().getAsInt());
      assertTrue(callback.wasTriggered());
      assertEquals(allianceStation.ordinal(), callback.getSetValue());

@@ -179,8 +189,8 @@ class DriverStationSimTest {
      DriverStationSim.setAllianceStationId(allianceStation);
      DriverStationSim.notifyNewData();
      assertEquals(allianceStation, DriverStationSim.getAllianceStationId());
-      assertEquals(DriverStation.Alliance.Red, DriverStation.getAlliance());
-      assertEquals(2, DriverStation.getLocation());
+      assertEquals(DriverStation.Alliance.Red, DriverStation.getAlliance().get());
+      assertEquals(2, DriverStation.getLocation().getAsInt());
      assertTrue(callback.wasTriggered());
      assertEquals(allianceStation.ordinal(), callback.getSetValue());

@@ -189,8 +199,8 @@ class DriverStationSimTest {
      DriverStationSim.setAllianceStationId(allianceStation);
      DriverStationSim.notifyNewData();
      assertEquals(allianceStation, DriverStationSim.getAllianceStationId());
-      assertEquals(DriverStation.Alliance.Red, DriverStation.getAlliance());
-      assertEquals(3, DriverStation.getLocation());
+      assertEquals(DriverStation.Alliance.Red, DriverStation.getAlliance().get());
+      assertEquals(3, DriverStation.getLocation().getAsInt());
      assertTrue(callback.wasTriggered());
      assertEquals(allianceStation.ordinal(), callback.getSetValue());
    }
--- a/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/digitalcommunication/Robot.java
+++ b/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/digitalcommunication/Robot.java
@@ -7,6 +7,7 @@ package edu.wpi.first.wpilibj.examples.digitalcommunication;
 import edu.wpi.first.wpilibj.DigitalOutput;
 import edu.wpi.first.wpilibj.DriverStation;
 import edu.wpi.first.wpilibj.TimedRobot;
+import java.util.Optional;

 /**
 * This is a sample program demonstrating how to communicate to a light controller from the robot
@@ -26,8 +27,14 @@ public class Robot extends TimedRobot {

  @Override
  public void robotPeriodic() {
+    boolean setAlliance = false;
+    Optional<DriverStation.Alliance> alliance = DriverStation.getAlliance();
+    if (alliance.isPresent()) {
+      setAlliance = alliance.get() == DriverStation.Alliance.Red;
+    }
+
    // pull alliance port high if on red alliance, pull low if on blue alliance
-    m_allianceOutput.set(DriverStation.getAlliance() == DriverStation.Alliance.Red);
+    m_allianceOutput.set(setAlliance);

    // pull enabled port high if enabled, low if disabled
    m_enabledOutput.set(DriverStation.isEnabled());
--- a/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/i2ccommunication/Robot.java
+++ b/wpilibjExamples/src/main/java/edu/wpi/first/wpilibj/examples/i2ccommunication/Robot.java
@@ -8,6 +8,7 @@ import edu.wpi.first.wpilibj.DriverStation;
 import edu.wpi.first.wpilibj.I2C;
 import edu.wpi.first.wpilibj.I2C.Port;
 import edu.wpi.first.wpilibj.TimedRobot;
+import java.util.Optional;

 /**
 * This is a sample program demonstrating how to communicate to a light controller from the robot
@@ -48,8 +49,14 @@ public class Robot extends TimedRobot {
    // alliance, enabled in teleop mode, with 43 seconds left in the match.
    StringBuilder stateMessage = new StringBuilder(6);

+    String allianceString = "U";
+    Optional<DriverStation.Alliance> alliance = DriverStation.getAlliance();
+    if (alliance.isPresent()) {
+      allianceString = alliance.get() == DriverStation.Alliance.Red ? "R" : "B";
+    }
+
    stateMessage
-        .append(DriverStation.getAlliance() == DriverStation.Alliance.Red ? "R" : "B")
+        .append(allianceString)
        .append(DriverStation.isEnabled() ? "E" : "D")
        .append(DriverStation.isAutonomous() ? "A" : "T")
        .append(String.format("%03d", (int) DriverStation.getMatchTime()));
--- a/wpilibjExamples/src/test/java/edu/wpi/first/wpilibj/examples/i2ccommunication/I2CCommunicationTest.java
+++ b/wpilibjExamples/src/test/java/edu/wpi/first/wpilibj/examples/i2ccommunication/I2CCommunicationTest.java
@@ -73,6 +73,9 @@ class I2CCommunicationTest {

    String str = assertTimeoutPreemptively(Duration.ofMillis(20L), () -> m_future.get());
    char expected = alliance.name().startsWith("Red") ? 'R' : 'B';
+    if (alliance.name().startsWith("Unknown")) {
+      expected = 'U';
+    }

    assertEquals(expected, str.charAt(0));
  }