WinAdapter does not enable UUID emulation on clang when C++ extensions are disabled

[Devaniti]

Description
When using DXC headers with clang compiler, headers fail to compile if C++ extensions were explicitly disabled.

Steps to Reproduce

1. In CMake project, set CMAKE_CXX_EXTENSIONS to OFF
2. Include WinAdapter.h in that same CMake project
3. Try to build the project and observe compile error

Not tested on Linux, but same bug likely exists there as well.
Workaround is to add #define __EMULATE_UUID 1 before including any DXC headers.

Actual Behavior
When including WinAdapter.h, line CROSS_PLATFORM_UUIDOF(IUnknown, "00000000-0000-0000-C000-000000000046") produces following errors:

error: expected parameter declarator
  572 | CROSS_PLATFORM_UUIDOF(IUnknown, "00000000-0000-0000-C000-000000000046")

REDACTED/DXC/inc/WinAdapter.h:572:33: error: expected ')'
REDACTED/DXC/inc/WinAdapter.h:572:1: note: to match this '('
  572 | CROSS_PLATFORM_UUIDOF(IUnknown, "00000000-0000-0000-C000-000000000046")

REDACTED/DXC/inc/WinAdapter.h:552:25: note: expanded from macro 'CROSS_PLATFORM_UUIDOF'
  552 |   struct __declspec(uuid(spec)) interface;
      |                         ^
REDACTED/DXC/inc/WinAdapter.h:572:23: error: expected function body after function declarator
  572 | CROSS_PLATFORM_UUIDOF(IUnknown, "00000000-0000-0000-C000-000000000046")

Environment

• DXC version - v1.8.2502
• Host Operating System - macOS 15.4
• Compiler - AppleClang 17.0.0.17000013

[damyanp]

WinAdapter.h is not intended to be a general purpose, reusable, header file so we don't plan to do specific work to make it more robust when used in different scenarios than building dxc.

[Devaniti]

It is included from dxcapi.h on non Windows platforms though -

DirectXShaderCompiler/include/dxc/dxcapi.h

Line 36 in 52c7c33

#include "WinAdapter.h"

To use DXC as a library on non Windows platforms, WinAdapter.h has to compile and implement relevant functionality properly

[damyanp]

Ah, thanks for the extra info. I'll reopen this.

If you've already figured out a work around for this, we'd welcome a PR!