Resolve Event Context Loss in Nested Event Cacnellation (#4529)

* Implement event context management in CEvents and CElement classes

* Refactor CEvents class to use a context stack instead of a single current context pointer

Author: MohabCodeX

Server/mods/deathmatch/logic/CElement.cpp

@@ -438,10 +438,11 @@ bool CElement::CallEvent(const char* szName, const CLuaArguments& Arguments, CPl
     if (!g_pGame->GetDebugHookManager()->OnPreEvent(szName, Arguments, this, pCaller))
         return false;
 
-    CEvents* pEvents = g_pGame->GetEvents();
+    CEvents*      pEvents = g_pGame->GetEvents();
+    CEventContext eventContext;
 
     // Make sure our event-manager knows we're about to call an event
-    pEvents->PreEventPulse();
+    pEvents->PreEventPulse(&eventContext);
 
     // Call the event on our parents/us first
     CallParentEvent(szName, Arguments, this, pCaller);
@@ -450,12 +451,12 @@ bool CElement::CallEvent(const char* szName, const CLuaArguments& Arguments, CPl
     CallEventNoParent(szName, Arguments, this, pCaller);
 
     // Tell the event manager that we're done calling the event
-    pEvents->PostEventPulse();
+    pEvents->PostEventPulse(&eventContext);
 
     g_pGame->GetDebugHookManager()->OnPostEvent(szName, Arguments, this, pCaller);
 
     // Return whether our event was cancelled or not
-    return (!pEvents->WasEventCancelled());
+    return !eventContext.IsCancelled();
 }
 
 bool CElement::DeleteEvent(CLuaMain* pLuaMain, const char* szName, const CLuaFunctionRef& iLuaFunction)

Server/mods/deathmatch/logic/CEvents.cpp

@@ -123,38 +123,68 @@ void CEvents::RemoveAllEvents()
     m_EventHashMap.clear();
 }
 
-void CEvents::PreEventPulse()
+void CEvents::PreEventPulse(CEventContext* pContext)
 {
+    assert(pContext);
+
     m_CancelledList.push_back(m_bEventCancelled);
+    m_ContextStack.push_back(pContext);
+
+    pContext->Reset();
+
     m_bEventCancelled = false;
     m_bWasEventCancelled = false;
     m_strLastError = "";
 }
 
-void CEvents::PostEventPulse()
+void CEvents::PostEventPulse(CEventContext* pContext)
 {
-    m_bWasEventCancelled = m_bEventCancelled;
+    assert(pContext);
+    assert(!m_ContextStack.empty());
+    assert(m_ContextStack.back() == pContext);
+
+    m_bWasEventCancelled = pContext->IsCancelled();
     m_bEventCancelled = m_CancelledList.back() ? true : false;
     m_CancelledList.pop_back();
+    m_ContextStack.pop_back();
 }
 
 void CEvents::CancelEvent(bool bCancelled)
 {
-    m_bEventCancelled = bCancelled;
+    CancelEvent(bCancelled, nullptr);
 }
 
 void CEvents::CancelEvent(bool bCancelled, const char* szReason)
 {
+    // ALWAYS set the old global variable for backward compatibility
     m_bEventCancelled = bCancelled;
-    m_strLastError = SStringX(szReason);
+    
+    // Also update context if it exists
+    if (!m_ContextStack.empty())
+    {
+        CEventContext* pCurrentContext = m_ContextStack.back();
+        if (bCancelled)
+            pCurrentContext->Cancel(szReason);
+        else
+            pCurrentContext->Reset();
+    }
+    
+    if (szReason)
+        m_strLastError = szReason;
 }
 
 bool CEvents::WasEventCancelled()
 {
-    return m_bWasEventCancelled;
+    if (!m_ContextStack.empty())
+        return m_ContextStack.back()->IsCancelled();
+    
+    return m_bEventCancelled || m_bWasEventCancelled;
 }
 
 const char* CEvents::GetLastError()
 {
+    if (!m_ContextStack.empty())
+        return m_ContextStack.back()->GetCancelReason().c_str();
+
     return m_strLastError;
 }

Server/mods/deathmatch/logic/CEvents.h

@@ -14,6 +14,7 @@
 #include <string>
 #include <list>
 #include <vector>
+#include "CEventContext.h"
 
 struct SEvent
 {
@@ -40,8 +41,8 @@ class CEvents
     CFastHashMap<SString, SEvent*>::const_iterator IterBegin() { return m_EventHashMap.begin(); };
     CFastHashMap<SString, SEvent*>::const_iterator IterEnd() { return m_EventHashMap.end(); };
 
-    void PreEventPulse();
-    void PostEventPulse();
+    void PreEventPulse(CEventContext* pContext);
+    void PostEventPulse(CEventContext* pContext);
 
     void        CancelEvent(bool bCancelled = true);
     void        CancelEvent(bool bCancelled, const char* szReason);
@@ -53,9 +54,10 @@ class CEvents
 
     CFastHashMap<SString, SEvent*> m_EventHashMap;
 
-    std::vector<int> m_CancelledList;
-    bool             m_bEventCancelled;
-    bool             m_bWasEventCancelled;
+    std::vector<int>               m_CancelledList;
+    bool                           m_bEventCancelled;
+    bool                           m_bWasEventCancelled;
+    SString                        m_strLastError;
 
-    SString m_strLastError;
+    std::vector<CEventContext*>    m_ContextStack;
 };

Shared/mods/deathmatch/logic/CEventContext.h

@@ -0,0 +1,40 @@
+/*****************************************************************************
+ *
+ *  PROJECT:     Multi Theft Auto
+ *  LICENSE:     See LICENSE in the top level directory
+ *  FILE:        Shared/mods/deathmatch/logic/CEventContext.h
+ *  PURPOSE:     Per-event context for event dispatch and cancellation
+ *
+ *  Multi Theft Auto is available from https://www.multitheftauto.com/
+ *
+ *****************************************************************************/
+
+#pragma once
+
+#include <string>
+
+class CEventContext
+{
+public:
+    CEventContext() noexcept : m_isCancelled(false) {}
+
+    void Cancel(const char* reason = nullptr) noexcept
+    {
+        m_isCancelled = true;
+        if (reason)
+            m_cancelReason = reason;
+    }
+
+    bool               IsCancelled() const noexcept { return m_isCancelled; }
+    const std::string& GetCancelReason() const noexcept { return m_cancelReason; }
+
+    void Reset() noexcept
+    {
+        m_isCancelled = false;
+        m_cancelReason.clear();
+    }
+
+private:
+    bool        m_isCancelled;
+    std::string m_cancelReason;
+};