build(cmake): Add ReactOS ATL and PSEH compatibility layer (TheSuperHackers#2067)

Add ReactOS Active Template Library (ATL) support for MinGW-w64 builds,
enabling ATL/COM functionality without MSVC dependencies. This provides
the ATL headers needed for COM-based browser control integration.

Components:
- ReactOS ATL headers (v0.4.15) fetched from ReactOS project
- ReactOS PSEH (exception handling) in C++-compatible dummy mode
- ATL compatibility header with MinGW-specific macro definitions
- PSEH compatibility header ensuring proper exception handling

The implementation uses ReactOS PSEH in dummy mode (_USE_DUMMY_PSEH)
because MinGW-w64's native PSEH uses GNU C nested functions which are
incompatible with C++. This provides ATL functionality needed for:
- CComPtr and CComBSTR smart pointers
- ATL string conversion macros
- COM interface implementations

Files:
- cmake/reactos-atl.cmake: ReactOS ATL integration
- Dependencies/Utility/Utility/atl_compat.h: ATL compatibility layer
- Dependencies/Utility/Utility/pseh_compat.h: PSEH compatibility layer
- CMakeLists.txt: Include ReactOS ATL configuration

Author: JohnsterID

CMakeLists.txt

@@ -41,6 +41,7 @@ include(FetchContent)
 # MinGW-w64 specific configuration
 if(MINGW)
     include(cmake/mingw.cmake)
+    include(cmake/reactos-atl.cmake)
     include(cmake/widl.cmake)
 endif()
 

Dependencies/Utility/Utility/atl_compat.h

@@ -0,0 +1,72 @@
+// TheSuperHackers @build JohnsterID 05/01/2026 Add ATL compatibility layer for MinGW-w64
+/**
+ * @file atl_compat.h
+ * @brief ATL compatibility layer for MinGW-w64 with ReactOS ATL
+ *
+ * Provides compatibility definitions for using ReactOS ATL headers
+ * with MinGW-w64 GCC compiler. Uses ReactOS PSEH in C++-compatible
+ * dummy mode (_USE_DUMMY_PSEH) because MinGW-w64's PSEH uses GNU C
+ * nested functions which are not valid in C++.
+ */
+
+#pragma once
+
+#ifdef __MINGW32__
+
+// Include Windows types needed for ATL compatibility
+#include <wtypes.h>
+
+// Include PSEH compatibility first (uses ReactOS PSEH in dummy mode)
+#include "pseh_compat.h"
+
+// Define _ATL_IIDOF macro for ReactOS ATL (uses MinGW-w64's __uuidof)
+#ifndef _ATL_IIDOF
+#define _ATL_IIDOF(x) __uuidof(x)
+#endif
+
+// Forward declare _Delegate function for COM aggregation support
+// ReactOS ATL's COM_INTERFACE_ENTRY_AGGREGATE macro uses _Delegate but doesn't define it
+// The actual function pointer will be defined after atlbase.h provides _ATL_CREATORARGFUNC
+extern "C" HRESULT WINAPI _ATL_DelegateQueryInterface(void* pv, REFIID riid, LPVOID* ppv, DWORD_PTR dw);
+
+// Suppress additional warnings from ReactOS ATL headers
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunknown-pragmas"
+#pragma GCC diagnostic ignored "-Wattributes"
+
+// NOTE: ReactOS ATL compile definitions are set in cmake/reactos-atl.cmake:
+//   - _ATL_CSTRING_EXPLICIT_CONSTRUCTORS
+//   - _ATL_NO_DEBUG_CRT
+//   - ATL_NO_ASSERT_ON_DESTROY_NONEXISTENT_WINDOW
+//   - ATL_NO_DEFAULT_LIBS
+// These are applied via target_compile_definitions() on the reactos_atl target.
+// Any target linking to reactos_atl will automatically inherit these definitions.
+//
+// IMPORTANT: _ATL_NO_AUTOMATIC_NAMESPACE is NOT defined because the codebase
+// uses ATL types (CComModule, CComObject, CString, etc.) without namespace
+// qualification and relies on the automatic 'using namespace ATL;' from ATL headers.
+
+// Define _Delegate implementation and macro now that ATL types are available
+inline HRESULT WINAPI _ATL_DelegateQueryInterface(void* pv, REFIID riid, LPVOID* ppv, DWORD_PTR dw)
+{
+    IUnknown** ppunk = reinterpret_cast<IUnknown**>(reinterpret_cast<char*>(pv) + dw);
+    if (*ppunk == NULL)
+        return E_NOINTERFACE;
+    return (*ppunk)->QueryInterface(riid, ppv);
+}
+
+#ifndef _Delegate
+#define _Delegate ((ATL::_ATL_CREATORARGFUNC*)_ATL_DelegateQueryInterface)
+#endif
+
+// Restore compiler warnings after ATL includes
+#define ATL_COMPAT_RESTORE_WARNINGS() \
+    do { \
+        _Pragma("GCC diagnostic pop") \
+        PSEH_COMPAT_RESTORE_WARNINGS() \
+    } while(0)
+
+#else
+// Non-MinGW platforms don't need these workarounds
+#define ATL_COMPAT_RESTORE_WARNINGS()
+#endif // __MINGW32__

Dependencies/Utility/Utility/pseh_compat.h

@@ -0,0 +1,34 @@
+// TheSuperHackers @build JohnsterID 05/01/2026 Add PSEH compatibility for MinGW-w64
+/**
+ * @file pseh_compat.h
+ * @brief PSEH compatibility for MinGW-w64 with ReactOS ATL
+ *
+ * ReactOS ATL headers include <pseh/pseh2.h>. This header ensures
+ * that ReactOS PSEH is used in C++-compatible dummy mode (_USE_DUMMY_PSEH).
+ * The cmake configuration (reactos-atl.cmake) adds ReactOS PSEH headers
+ * to the include path before system headers, and defines _USE_DUMMY_PSEH.
+ */
+
+#pragma once
+
+#ifdef __MINGW32__
+
+// Suppress PSEH-related warnings from ReactOS PSEH headers
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunknown-pragmas"
+#pragma GCC diagnostic ignored "-Wattributes"
+#pragma GCC diagnostic ignored "-Wunused-variable"
+#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
+#pragma GCC diagnostic ignored "-Wunused-label"
+
+// ReactOS PSEH headers will be included by ATL headers
+// No need to include them explicitly here
+
+// Restore compiler warnings after PSEH includes
+#define PSEH_COMPAT_RESTORE_WARNINGS() \
+    _Pragma("GCC diagnostic pop")
+
+#else
+// Non-MinGW platforms use native SEH or don't need PSEH
+#define PSEH_COMPAT_RESTORE_WARNINGS()
+#endif // __MINGW32__

cmake/reactos-atl.cmake

@@ -0,0 +1,63 @@
+# TheSuperHackers @build JohnsterID 05/01/2026 Add ReactOS ATL and PSEH compatibility for MinGW
+# ReactOS ATL headers for MinGW-w64 builds
+# Provides ATL/COM support without MSVC dependencies
+# Uses ReactOS PSEH in C++-compatible dummy mode (_USE_DUMMY_PSEH)
+# because MinGW-w64's PSEH uses GNU C nested functions which don't work in C++
+
+if(MINGW)
+    message(STATUS "Setting up ReactOS ATL for MinGW-w64")
+    
+    FetchContent_Declare(
+        reactos_atl
+        GIT_REPOSITORY https://github.com/reactos/reactos.git
+        GIT_TAG        0.4.15-release
+        GIT_SHALLOW    TRUE
+        GIT_PROGRESS   TRUE
+        SOURCE_SUBDIR  sdk/lib/atl
+    )
+    
+    FetchContent_GetProperties(reactos_atl)
+    if(NOT reactos_atl_POPULATED)
+        FetchContent_Populate(reactos_atl)
+        
+        # Create interface library for ReactOS ATL headers
+        add_library(reactos_atl INTERFACE)
+        
+        # Add ReactOS ATL and PSEH include directories with SYSTEM to suppress warnings
+        # ReactOS PSEH must come BEFORE system includes to override MinGW's pseh2.h
+        # (MinGW's pseh2.h uses GNU C nested functions which don't work in C++)
+        # NOTE: Do NOT include ReactOS CRT headers - use MinGW-w64's CRT instead
+        target_include_directories(reactos_atl SYSTEM INTERFACE 
+            "${reactos_atl_SOURCE_DIR}/sdk/lib/pseh/include"
+            "${reactos_atl_SOURCE_DIR}/sdk/lib/atl"
+        )
+        
+        # COM support (_com_util::ConvertStringToBSTR and ConvertBSTRToString)
+        # is provided by Dependencies/Utility/Utility/comsupp_compat.h as a
+        # header-only implementation. No library needs to be built or linked.
+        
+        # Add required ATL defines for MinGW compatibility
+        # NOTE: Do NOT define _ATL_NO_AUTOMATIC_NAMESPACE
+        # The codebase uses ATL types (CComModule, CComObject, CString, etc.)
+        # without ATL:: qualification and relies on automatic 'using namespace ATL;'
+        #
+        # _USE_DUMMY_PSEH: Use ReactOS PSEH's C++-compatible "dummy" mode
+        # which provides simple macros instead of GNU C nested functions
+        target_compile_definitions(reactos_atl INTERFACE
+            _ATL_CSTRING_EXPLICIT_CONSTRUCTORS
+            _ATL_NO_DEBUG_CRT
+            ATL_NO_ASSERT_ON_DESTROY_NONEXISTENT_WINDOW
+            ATL_NO_DEFAULT_LIBS
+            _USE_DUMMY_PSEH
+        )
+        
+        message(STATUS "ReactOS ATL headers: ${reactos_atl_SOURCE_DIR}/sdk/lib/atl")
+        message(STATUS "ReactOS PSEH headers: ${reactos_atl_SOURCE_DIR}/sdk/lib/pseh/include")
+        message(STATUS "COM support (comsupp): Header-only in Dependencies/Utility/Utility/comsupp_compat.h")
+        message(STATUS "Using ReactOS PSEH in C++-compatible dummy mode (_USE_DUMMY_PSEH)")
+        message(STATUS "Using MinGW-w64 CRT headers (NOT ReactOS CRT)")
+    endif()
+else()
+    # Create dummy target for non-MinGW builds
+    add_library(reactos_atl INTERFACE)
+endif()