[commands] Fix C++ iterator invalidation bug (#7554)

Co-authored-by: Joseph Eng <91924258+KangarooKoala@users.noreply.github.com>
Co-authored-by: Ryan Blue <13878527+rzblue@users.noreply.github.com>

wpilibNewCommands/src/test/native/cpp/frc2/command/CommandScheduleTest.cpp

@@ -6,6 +6,9 @@
 #include <networktables/NetworkTableInstance.h>
 
 #include "CommandTestBase.h"
+#include "frc2/command/FunctionalCommand.h"
+#include "frc2/command/InstantCommand.h"
+#include "frc2/command/RunCommand.h"
 
 using namespace frc2;
 class CommandScheduleTest : public CommandTestBase {};
@@ -95,6 +98,51 @@ TEST_F(CommandScheduleTest, SchedulerCancel) {
   EXPECT_FALSE(scheduler.IsScheduled(&command));
 }
 
+TEST_F(CommandScheduleTest, CommandKnowsWhenItEnded) {
+  CommandScheduler scheduler = GetScheduler();
+
+  frc2::FunctionalCommand* commandPtr = nullptr;
+  auto command = frc2::FunctionalCommand(
+      [] {}, [] {},
+      [&](auto isForced) {
+        EXPECT_FALSE(scheduler.IsScheduled(commandPtr))
+            << "Command shouldn't be scheduled when its end is called";
+      },
+      [] { return true; });
+  commandPtr = &command;
+
+  scheduler.Schedule(commandPtr);
+  scheduler.Run();
+  EXPECT_FALSE(scheduler.IsScheduled(commandPtr))
+      << "Command should be removed from scheduler when its isFinished() "
+         "returns true";
+}
+
+TEST_F(CommandScheduleTest, ScheduleCommandInCommand) {
+  CommandScheduler scheduler = GetScheduler();
+  int counter = 0;
+  frc2::InstantCommand commandToGetScheduled{[&counter] { counter++; }};
+
+  auto command =
+      frc2::RunCommand([&counter, &scheduler, &commandToGetScheduled] {
+        scheduler.Schedule(&commandToGetScheduled);
+        EXPECT_EQ(counter, 1)
+            << "Scheduled command's init was not run immediately "
+               "after getting scheduled";
+      });
+
+  scheduler.Schedule(&command);
+  scheduler.Run();
+  EXPECT_EQ(counter, 1) << "Command 2 was not run when it should have been";
+  EXPECT_TRUE(scheduler.IsScheduled(&commandToGetScheduled))
+      << "Command 2 was not added to scheduler";
+
+  scheduler.Run();
+  EXPECT_EQ(counter, 1) << "Command 2 was run when it shouldn't have been";
+  EXPECT_FALSE(scheduler.IsScheduled(&commandToGetScheduled))
+      << "Command 2 did not end when it should have";
+}
+
 TEST_F(CommandScheduleTest, NotScheduledCancel) {
   CommandScheduler scheduler = GetScheduler();
   MockCommand command;

wpilibNewCommands/src/test/native/cpp/frc2/command/SchedulingRecursionTest.cpp

@@ -339,6 +339,45 @@ TEST_F(SchedulingRecursionTest, CancelDefaultCommandFromEnd) {
   EXPECT_TRUE(scheduler.IsScheduled(&other));
 }
 
+TEST_F(SchedulingRecursionTest, CancelNextCommandFromCommand) {
+  CommandScheduler scheduler = GetScheduler();
+
+  frc2::RunCommand* command1Ptr = nullptr;
+  frc2::RunCommand* command2Ptr = nullptr;
+  int counter = 0;
+
+  auto command1 = frc2::RunCommand([&counter, &command2Ptr, &scheduler] {
+    scheduler.Cancel(command2Ptr);
+    counter++;
+  });
+  auto command2 = frc2::RunCommand([&counter, &command1Ptr, &scheduler] {
+    scheduler.Cancel(command1Ptr);
+    counter++;
+  });
+
+  command1Ptr = &command1;
+  command2Ptr = &command2;
+
+  scheduler.Schedule(&command1);
+  scheduler.Schedule(&command2);
+  scheduler.Run();
+
+  EXPECT_EQ(counter, 1) << "Second command was run when it shouldn't have been";
+
+  // only one of the commands should be canceled.
+  EXPECT_FALSE(scheduler.IsScheduled(&command1) &&
+               scheduler.IsScheduled(&command2))
+      << "Both commands are running when only one should be";
+  // one of the commands shouldn't be canceled because the other one is canceled
+  // first
+  EXPECT_TRUE(scheduler.IsScheduled(&command1) ||
+              scheduler.IsScheduled(&command2))
+      << "Both commands are canceled when only one should be";
+
+  scheduler.Run();
+  EXPECT_EQ(counter, 2);
+}
+
 INSTANTIATE_TEST_SUITE_P(
     SchedulingRecursionTests, SchedulingRecursionTest,
     testing::Values(Command::InterruptionBehavior::kCancelSelf,