[wpilibc] Remove Alert magic static with map lookup

The magic static adds yet another thing that needs to be reset if you
want to run a unit test with a completely reset wpilib state. Use the
existing Sendable static map to store the data instead.

This leaks memory if ResetSmartDashboardInstance is called.

wpilibc/src/main/native/cpp/Alert.cpp

@@ -82,17 +82,18 @@ class Alert::SendableAlerts : public nt::NTSendable,
    * @return the SendableAlerts for the group
    */
   static SendableAlerts& ForGroup(std::string_view group) {
-    // Force initialization of SendableRegistry before our magic static to
-    // prevent incorrect destruction order.
-    wpi::SendableRegistry::EnsureInitialized();
-    static wpi::StringMap<Alert::SendableAlerts> groups;
-
-    auto [iter, exists] = groups.try_emplace(group);
-    SendableAlerts& sendable = iter->second;
-    if (!exists) {
-      frc::SmartDashboard::PutData(group, &iter->second);
+    SendableAlerts* salert = nullptr;
+    try {
+      auto* sendable = frc::SmartDashboard::GetData(group);
+      salert = dynamic_cast<SendableAlerts*>(sendable);
+    } catch (frc::RuntimeError&) {
     }
-    return sendable;
+    if (!salert) {
+      // this leaks if ResetSmartDashboardInstance is called, but that's fine
+      salert = new Alert::SendableAlerts;
+      frc::SmartDashboard::PutData(group, salert);
+    }
+    return *salert;
   }
 
  private:

wpilibc/src/test/native/cpp/AlertTest.cpp

@@ -33,8 +33,7 @@ class AlertsTest : public ::testing::Test {
   std::string GetGroupName() {
     const ::testing::TestInfo* testInfo =
         ::testing::UnitTest::GetInstance()->current_test_info();
-    return fmt::format("{}_{}", testInfo->test_suite_name(),
-                       testInfo->test_case_name());
+    return fmt::format("{}_{}", testInfo->test_suite_name(), testInfo->name());
   }
 
   template <typename... Args>
@@ -80,7 +79,16 @@ class AlertsTest : public ::testing::Test {
 #define EXPECT_STATE(type, ...) \
   EXPECT_EQ(GetActiveAlerts(type), (std::vector<std::string>{__VA_ARGS__}))
 
-TEST_F(AlertsTest, SetUnset) {
+TEST_F(AlertsTest, SetUnsetSingle) {
+  auto one = MakeAlert("one", kInfo);
+  EXPECT_FALSE(IsAlertActive("one", kInfo));
+  one.Set(true);
+  EXPECT_TRUE(IsAlertActive("one", kInfo));
+  one.Set(false);
+  EXPECT_FALSE(IsAlertActive("one", kInfo));
+}
+
+TEST_F(AlertsTest, SetUnsetMultiple) {
   auto one = MakeAlert("one", kError);
   auto two = MakeAlert("two", kInfo);
   EXPECT_FALSE(IsAlertActive("one", kError));