common: fix: export CodeFragment/SharedDataManager with INET_API (Windows link error)

On Windows/MinGW, linking a project against INET's shared library failed to
resolve symbols defined in Compat.h -- e.g. CodeFragment's constructor, which
backs Register_Serializer and the other EXECUTE_* / Define_InitStage macros --
because the OMNETPP_BUILDNUM<2000 compat classes CodeFragment and
SharedDataManager were declared without INET_API and so were never dllexported.

Simply adding INET_API to the two classes does not compile, because INETDefs.h
included Compat.h before defining INET_API (the macro was an undefined token at
the declarations). Fix the ordering: move the Compat.h/ParsimPacking.h includes
below the INET_API definition in INETDefs.h, and make the two files that
included Compat.h directly (Compat.cc, QueueVisualizerBase.h) include INETDefs.h
instead. Add a guard to Compat.h that rejects direct inclusion with a clear
error, since it uses INET_API but does not define it.

No effect on non-Windows builds (INET_API is empty there). Verified by a full
release build.

Fixes #1108.

Author: avarga

src/inet/common/Compat.cc

@@ -5,7 +5,7 @@
 //
 
 
-#include "inet/common/Compat.h"
+#include "inet/common/INETDefs.h" // pulls in Compat.h after INET_API is defined
 
 namespace inet {
 

src/inet/common/Compat.h

@@ -8,6 +8,13 @@
 #ifndef __INET_COMPAT_H
 #define __INET_COMPAT_H
 
+// This is an internal compatibility shim: it declares INET_API-exported classes
+// but relies on INETDefs.h to define INET_API beforehand. It must therefore be
+// reached only through inet/common/INETDefs.h, never included directly.
+#ifndef __INET_INETDEFS_H
+#error "Do not include inet/common/Compat.h directly; include inet/common/INETDefs.h instead."
+#endif
+
 #include <omnetpp.h>
 
 #include <functional>
@@ -39,7 +46,7 @@ typedef int sharedcounterhandle_t;
  * This class encapsulates the "simulation-global variables" functionality which became
  * part of the cSimulation class in OMNeT++ 7.0.
  */
-class SharedDataManager : public omnetpp::cISimulationLifecycleListener
+class INET_API SharedDataManager : public omnetpp::cISimulationLifecycleListener
 {
   private:
     struct SharedDataHandles {
@@ -186,7 +193,7 @@ T& SharedDataManager::getSharedVariable(int handle, Args&&... args)
  * Supporting class for EXECUTE_PRE_NETWORK_SETUP() / EXECUTE_POST_NETWORK_DELETE(),
  * which didn't exist prior to OMNeT++ 7.0.
  */
-class CodeFragment
+class INET_API CodeFragment
 {
   private:
     omnetpp::SimulationLifecycleEventType lifecycleEvent;

src/inet/common/INETDefs.h

@@ -25,9 +25,6 @@
 // General definitions.
 //
 
-#include "inet/common/Compat.h"
-#include "inet/common/ParsimPacking.h"
-
 namespace inet {
 using namespace omnetpp;
 using omnetpp::operator<<;
@@ -48,6 +45,12 @@ using omnetpp::operator<<;
 #define INET_API
 #endif // if defined(INET_EXPORT)
 
+// Compat.h declares exported classes (e.g. CodeFragment) using INET_API, so it
+// must be included only after INET_API is defined above. ParsimPacking.h is
+// kept alongside it.
+#include "inet/common/Compat.h"
+#include "inet/common/ParsimPacking.h"
+
 #include "inet/common/InitStages.h"
 
 #ifndef SIMTIME_RAW_T_DEFINED

src/inet/visualizer/base/QueueVisualizerBase.h

@@ -8,7 +8,7 @@
 #ifndef __INET_QUEUEVISUALIZERBASE_H
 #define __INET_QUEUEVISUALIZERBASE_H
 
-#include "inet/common/Compat.h"
+#include "inet/common/INETDefs.h"
 #include "inet/queueing/contract/IPacketQueue.h"
 #include "inet/visualizer/base/VisualizerBase.h"
 #include "inet/visualizer/util/Placement.h"