Add a define (WINRT_NEVER_REG_FREE) that will break the build if linked against something using WINRT_REG_FREE

Author: dmachaj

strings/base_activation.h

@@ -108,8 +108,17 @@ namespace winrt::impl
         return 0U;
     }();
 
+    // This pragma is used to detect if the translation unit containing regfree usage is being linked with another translation
+    // unit that declared WINRT_NEVER_REG_FREE.
+#pragma detect_mismatch("WINRT_REG_FREE", "enabled")
 #endif // WINRT_REG_FREE
 
+#ifdef WINRT_NEVER_REG_FREE
+    // This pragma is used to ensure that a binary will never have winrt regfree logic enabled.  Defining WINRT_NEVER_REG_FREE will
+    // cause this pragma to break linkage if any translation units in the same binary defined WINRT_REG_FREE.
+#pragma detect_mismatch("WINRT_REG_FREE", "never")
+#endif // WINRT_NEVER_REG_FREE
+
     template <typename Interface>
     hresult get_runtime_activation_factory(param::hstring const& name, void** result) noexcept
     {

test/test_cpp20/activation_without_regfree.cpp

@@ -1,10 +1,6 @@
 #include "pch.h"
 #include "winrt/test_component.h"
 
-#ifdef WINRT_REG_FREE
-#error "This test needs WINRT_REG_FREE to be undefined"
-#endif
-
 using namespace winrt;
 using namespace Windows::Foundation;
 using namespace test_component;

test/test_cpp20/pch.h

@@ -3,6 +3,7 @@
 #pragma warning(4: 4458) // ensure we compile clean with this warning enabled
 
 #define WINRT_LEAN_AND_MEAN
+#define WINRT_NEVER_REG_FREE
 #include <unknwn.h>
 #include "winrt/Windows.Data.Json.h"
 #include "winrt/Windows.Foundation.h"