Fix src/lib/support/StateMachine pattern matching

The Enter method can rewrite the state objects during pattern matching
traversal.  We need a one-shot bool to ensure we only execute
Enter once.  And although state changes from Exit, LogTransition and
GetName aren't expected, we should check in these too.  In all cases,
the pattern match should only execute once.

src/lib/support/StateMachine.h

@@ -48,37 +48,40 @@ struct VariantState : Variant<Ts...>
 
 private:
     template <typename T>
-    void Enter()
+    void Enter(bool & ever)
     {
-        if (chip::Variant<Ts...>::template Is<T>())
+        if (!ever && chip::Variant<Ts...>::template Is<T>())
         {
+            ever = true;
             chip::Variant<Ts...>::template Get<T>().Enter();
         }
     }
 
     template <typename T>
-    void Exit()
+    void Exit(bool & ever)
     {
-        if (chip::Variant<Ts...>::template Is<T>())
+        if (!ever && chip::Variant<Ts...>::template Is<T>())
         {
+            ever = true;
             chip::Variant<Ts...>::template Get<T>().Exit();
         }
     }
 
     template <typename T>
     void GetName(const char ** name)
     {
-        if (name && chip::Variant<Ts...>::template Is<T>())
+        if (name && !*name && chip::Variant<Ts...>::template Is<T>())
         {
             *name = chip::Variant<Ts...>::template Get<T>().GetName();
         }
     }
 
     template <typename T>
-    void LogTransition(const char * previous)
+    void LogTransition(bool & ever, const char * previous)
     {
-        if (chip::Variant<Ts...>::template Is<T>())
+        if (!ever && chip::Variant<Ts...>::template Is<T>())
         {
+            ever = true;
             chip::Variant<Ts...>::template Get<T>().LogTransition(previous);
         }
     }
@@ -94,12 +97,14 @@ struct VariantState : Variant<Ts...>
 
     void Enter()
     {
-        [](...) {}((this->template Enter<Ts>(), 0)...);
+        bool ever = false;
+        [](...) {}((this->template Enter<Ts>(ever), 0)...);
     }
 
     void Exit()
     {
-        [](...) {}((this->template Exit<Ts>(), 0)...);
+        bool ever = false;
+        [](...) {}((this->template Exit<Ts>(ever), 0)...);
     }
 
     const char * GetName()
@@ -111,7 +116,8 @@ struct VariantState : Variant<Ts...>
 
     void LogTransition(const char * previous)
     {
-        [](...) {}((this->template LogTransition<Ts>(previous), 0)...);
+        bool ever = false;
+        [](...) {}((this->template LogTransition<Ts>(ever, previous), 0)...);
     }
 };
 
@@ -215,10 +221,10 @@ class StateMachine : public Context<TEvent>
         auto newState = mTransitions(mCurrentState, evt);
         if (newState.HasValue())
         {
-            auto oldState = mCurrentState;
-            oldState.Exit();
+            auto oldState = mCurrentState.GetName();
+            mCurrentState.Exit();
             mCurrentState = newState.Value();
-            mCurrentState.LogTransition(oldState.GetName());
+            mCurrentState.LogTransition(oldState);
             // It is impermissible to dispatch events from Exit() or
             // LogTransition(), or from the transitions table when a transition
             // has also been returned.  Verify that this hasn't occurred.