Compiling Qt 5 with MinGW 11.2 on Windows

Prerequisites:

• Visual Studio, with fxc.exe from Windows Kits
• MinGW 11.2 from Qt official installer

1. Checkout the kde/5.15 branch from invent.kde.org
2. In a x64 Visual Studio dev prompt: where fxc.exe. Then add that directory to the PATH.
3. Add the MinGW bin/ folder to PATH (typically C:\Qt\Tools\mingw1120_64 for the official Qt installer).
4. Apply this diff to qtdeclarative to fix D3D12 FTBFS issues [1]:

diff --git a/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp b/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp
index 75bde2c66b..3594878eca 100644
--- a/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp
+++ b/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp
@@ -221,7 +221,7 @@ static void getHardwareAdapter(IDXGIFactory1 *factory, IDXGIAdapter1 **outAdapte
         if (SUCCEEDED(factory->EnumAdapters1(adapterIndex, &adapter))) {
             adapter->GetDesc1(&desc);
             const QString name = QString::fromUtf16((char16_t *) desc.Description);
-            HRESULT hr = D3D12CreateDevice(adapter.Get(), fl, _uuidof(ID3D12Device), nullptr);
+            HRESULT hr = D3D12CreateDevice(adapter.Get(), fl, __uuidof(ID3D12Device), nullptr);
             if (SUCCEEDED(hr)) {
                 qCDebug(QSG_LOG_INFO_GENERAL, "Using requested adapter '%s'", qPrintable(name));
                 *outAdapter = adapter.Detach();
@@ -238,7 +238,7 @@ static void getHardwareAdapter(IDXGIFactory1 *factory, IDXGIAdapter1 **outAdapte
         if (desc.Flags & DXGI_ADAPTER_FLAG_SOFTWARE)
             continue;

-        if (SUCCEEDED(D3D12CreateDevice(adapter.Get(), fl, _uuidof(ID3D12Device), nullptr))) {
+        if (SUCCEEDED(D3D12CreateDevice(adapter.Get(), fl, __uuidof(ID3D12Device), nullptr))) {
             const QString name = QString::fromUtf16((char16_t *) desc.Description);
             qCDebug(QSG_LOG_INFO_GENERAL, "Using adapter '%s'", qPrintable(name));
             break;
diff --git a/src/plugins/scenegraph/d3d12/qsgd3d12engine_p_p.h b/src/plugins/scenegraph/d3d12/qsgd3d12engine_p_p.h
index a95cbb1cbb..54a2c4dc8f 100644
--- a/src/plugins/scenegraph/d3d12/qsgd3d12engine_p_p.h
+++ b/src/plugins/scenegraph/d3d12/qsgd3d12engine_p_p.h
@@ -55,6 +55,7 @@
 #include <QCache>

 #include <d3d12.h>
+#include <d3d12sdklayers.h>
 #include <dxgi1_4.h>
 #include <dcomp.h>
 #include <wrl/client.h>
@@ -263,8 +264,8 @@ private:
     void beginFrameDraw();
     void endDrawCalls(bool lastInFrame = false);

-    static const int MAX_SWAP_CHAIN_BUFFER_COUNT = 4;
-    static const int MAX_FRAME_IN_FLIGHT_COUNT = 4;
+    static inline const int MAX_SWAP_CHAIN_BUFFER_COUNT = 4;
+    static inline const int MAX_FRAME_IN_FLIGHT_COUNT = 4;

     bool initialized = false;
     bool inFrame = false;

5. Then apply this diff to qtbase to compile qmake faster:

diff --git a/configure.bat b/configure.bat
index b34e146f5f..2ba220ee32 100644
--- a/configure.bat
+++ b/configure.bat
@@ -182,7 +182,7 @@ if "%PLATFORM:g++=%" == "%PLATFORM%" (
     set tmpl=win32
 ) else (
     if "%MAKE%" == "" (
-        set MAKE=mingw32-make
+        set MAKE=mingw32-make -j%NUMBER_OF_PROCESSORS%
     )
     set tmpl=unix
 )

6. The compile will fail with either gl/gl.h not found or a debug postfix issue for one of the examples, so be sure to add -opengl desktop -nomake examples to the configure command.

[1]. https://forum.qt.io/topic/128587/build-failure-_uuidof-was-not-declared-in-this-scope