- allow loading Zips where all content is in a subdirectory.

The same logic as in GZDoom applies: The root must not have any other content and the subdirectory must contain identifiable game content.
Some handling was also added to strip out macOS resource fork folders because they can contain data that can confuse file detection.

source/common/filesystem/file_zip.cpp

@@ -233,12 +233,14 @@ bool FZipFile::Open(bool quiet, LumpFilterInfo* filter)
 		}
 
 		name.ToLower();
+		if (name.IndexOf("__macosx") == 0) 
+			continue; // skip Apple garbage. At this stage only the root folder matters,
 		if (i == 0)
 		{
 			// check for special names, if one of these gets found this must be treated as a normal zip.
 			bool isspecial = name.IndexOf("/") < 0 || (filter && filter->reservedFolders.Find(name) < filter->reservedFolders.Size());
 			if (isspecial) break;
-			name0 = name;
+			name0 = name.Left(name.LastIndexOf("/")+1);
 		}
 		else
 		{
@@ -252,7 +254,7 @@ bool FZipFile::Open(bool quiet, LumpFilterInfo* filter)
 				// at least one of the more common definition lumps must be present.
 				for (auto &p : filter->requiredPrefixes)
 				{ 
-					if (name.IndexOf(name0 + p) == 0)
+					if (name.IndexOf(name0 + p) == 0 || name.LastIndexOf(p) == name.Len() - strlen(p))
 					{
 						foundspeciallump = true;
 						break;
@@ -272,7 +274,6 @@ bool FZipFile::Open(bool quiet, LumpFilterInfo* filter)
 
 		int len = LittleShort(zip_fh->NameLength);
 		FString name(dirptr + sizeof(FZipCentralDirectoryInfo), len);
-		if (name0.IsNotEmpty()) name = name.Mid(name0.Len());
 		dirptr += sizeof(FZipCentralDirectoryInfo) + 
 				  LittleShort(zip_fh->NameLength) + 
 				  LittleShort(zip_fh->ExtraLength) + 
@@ -284,7 +285,14 @@ bool FZipFile::Open(bool quiet, LumpFilterInfo* filter)
 			if (!quiet) Printf(TEXTCOLOR_RED "\n%s: Central directory corrupted.", FileName.GetChars());
 			return false;
 		}
-		
+
+		if (name.IndexOf("__macosx") == 0 || name.IndexOf("__MACOSX") == 0)
+		{
+			skipped++;
+			continue; // Weed out Apple's resource fork garbage right here because it interferes with safe operation.
+		}
+		if (name0.IsNotEmpty()) name = name.Mid(name0.Len());
+
 		// skip Directories
 		if (name.IsEmpty() || (name.Back() == '/' && LittleLong(zip_fh->UncompressedSize) == 0))
 		{

source/core/initfs.cpp

@@ -274,6 +274,18 @@ static void DeleteStuff(FileSystem &fileSystem, const TArray<FString>& deletelum
 //
 //
 //==========================================================================
+const char* iwad_folders[13] = { "textures/", "hires/", "sounds/", "music/", "maps/" };
+const char* iwad_reserved_duke[12] = { ".map", ".con", "menudef", "gldefs", "zscript", "maps/", nullptr };
+const char* iwad_reserved_blood[12] = { ".map", ".ini", "menudef", "gldefs", "zscript", "maps/", nullptr };
+const char* iwad_reserved_sw[12] = { ".map", "swcustom.txt", "menudef", "gldefs", "zscript", "maps/", nullptr };
+const char* iwad_reserved_ex[12] = { ".map", "menudef", "gldefs", "zscript", "maps/", nullptr };
+
+const char** iwad_reserved()
+{
+	return (g_gameType & GAMEFLAG_PSEXHUMED) ? iwad_reserved_ex :
+		(g_gameType & GAMEFLAG_SW) ? iwad_reserved_sw :
+		(g_gameType & GAMEFLAG_BLOOD) ? iwad_reserved_blood : iwad_reserved_duke;
+}
 
 void InitFileSystem(TArray<GrpEntry>& groups)
 {
@@ -374,6 +386,8 @@ void InitFileSystem(TArray<GrpEntry>& groups)
 	}
 	todelete.Append(userConfig.toBeDeleted);
 	LumpFilterInfo lfi;
+	for (auto p : iwad_folders) lfi.reservedFolders.Push(p);
+	for (auto p = iwad_reserved(); *p; p++) lfi.requiredPrefixes.Push(*p);
 
 	lfi.dotFilter = LumpFilter;