Fix autosave build for DVL_NO_FILESYSTEM targets

Fall back to the regular save flow when UNPACKED_SAVES builds have no filesystem support, compile backup-copy restore paths only when filesystem support is available, and keep demo helpers as documented stubs in that configuration.

Source/loadsave.cpp

@@ -2929,6 +2929,11 @@ void SaveGameData(SaveWriter &saveWriter)
 void SaveGame()
 {
 	gbValidSaveFile = true;
+
+#if defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM)
+	pfile_write_hero(/*writeGameData=*/true);
+	sfile_write_stash();
+#else
 	const bool heroSaved = pfile_write_hero_with_backup(/*writeGameData=*/true);
 	if (!heroSaved) {
 		gbValidSaveFile = false;
@@ -2939,6 +2944,7 @@ void SaveGame()
 		gbValidSaveFile = false;
 		return;
 	}
+#endif
 }
 
 void SaveLevel(SaveWriter &saveWriter)

Source/pfile.cpp

@@ -165,17 +165,15 @@ SaveWriter GetSaveWriter(uint32_t saveNum)
 	return SaveWriter(GetSavePath(saveNum));
 }
 
-SaveWriter GetStashWriter()
-{
-	return SaveWriter(GetStashSavePath());
-}
-
+SaveWriter GetStashWriter()
+{
+	return SaveWriter(GetStashSavePath());
+}
+
+#if !(defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM))
 void CopySaveLocation(const std::string &sourceLocation, const std::string &targetLocation)
 {
 #if defined(UNPACKED_SAVES)
-#ifdef DVL_NO_FILESYSTEM
-#error "UNPACKED_SAVES requires either DISABLE_DEMOMODE or C++17 <filesystem>"
-#endif
 	if (!targetLocation.empty()) {
 		CreateDir(targetLocation.c_str());
 	}
@@ -191,9 +189,6 @@ void CopySaveLocation(const std::string &sourceLocation, const std::string &targ
 void RestoreSaveLocation(const std::string &targetLocation, const std::string &backupLocation)
 {
 #if defined(UNPACKED_SAVES)
-#ifdef DVL_NO_FILESYSTEM
-#error "UNPACKED_SAVES requires either DISABLE_DEMOMODE or C++17 <filesystem>"
-#endif
 	if (DirectoryExists(targetLocation.c_str())) {
 		for (const std::filesystem::directory_entry &entry : std::filesystem::directory_iterator(targetLocation))
 			RemoveFile(entry.path().string().c_str());
@@ -207,6 +202,7 @@ void RestoreSaveLocation(const std::string &targetLocation, const std::string &b
 	CopyFileOverwrite(backupLocation.c_str(), targetLocation.c_str());
 #endif
 }
+#endif
 
 void Game2UiPlayer(const Player &player, _uiheroinfo *heroinfo, bool bHasSaveFile)
 {
@@ -641,12 +637,13 @@ const char *pfile_get_password()
 	return gbIsMultiplayer ? PASSWORD_MULTI : PASSWORD_SINGLE;
 }
 
-void pfile_write_hero(bool writeGameData)
-{
-	SaveWriter saveWriter = GetSaveWriter(gSaveNumber);
-	pfile_write_hero(saveWriter, writeGameData);
-}
-
+void pfile_write_hero(bool writeGameData)
+{
+	SaveWriter saveWriter = GetSaveWriter(gSaveNumber);
+	pfile_write_hero(saveWriter, writeGameData);
+}
+
+#if !(defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM))
 bool pfile_write_hero_with_backup(bool writeGameData)
 {
 	const std::string backupPrefix = "backup_";
@@ -696,8 +693,10 @@ bool pfile_write_stash_with_backup()
 
 	return false;
 }
-
-#ifndef DISABLE_DEMOMODE
+#endif
+
+#ifndef DISABLE_DEMOMODE
+#if !(defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM))
 void pfile_write_hero_demo(int demo)
 {
 	const std::string saveLocation = GetSavePath(gSaveNumber, StrCat("demo_", demo, "_reference_"));
@@ -719,13 +718,27 @@ HeroCompareResult pfile_compare_hero_demo(int demo, bool logDetails)
 		SaveWriter saveWriter(actualSavePath.c_str());
 		pfile_write_hero(saveWriter, true);
 	}
-
-	return CompareSaves(actualSavePath, referenceSavePath, logDetails);
-}
-#endif
-
-void sfile_write_stash()
-{
+
+	return CompareSaves(actualSavePath, referenceSavePath, logDetails);
+}
+#else
+// Demo save comparison is unavailable on UNPACKED_SAVES targets without filesystem support.
+void pfile_write_hero_demo(int demo)
+{
+	(void)demo;
+}
+
+HeroCompareResult pfile_compare_hero_demo(int demo, bool logDetails)
+{
+	(void)demo;
+	(void)logDetails;
+	return { HeroCompareResult::ReferenceNotFound, {} };
+}
+#endif
+#endif
+
+void sfile_write_stash()
+{
 	if (!Stash.dirty)
 		return;