From 14ca0189987f3ca476d6aa4cd10357040c569a04 Mon Sep 17 00:00:00 2001
From: Charles Milette <charles.milette@gmail.com>
Date: Sat, 1 Oct 2022 19:10:14 -0400
Subject: [PATCH 1/2] Fix classic COM errors on non-supported compilers

Also, enable fast path for Clang and give friendlier errors to MSVC
---
 strings/base_meta.h | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/strings/base_meta.h b/strings/base_meta.h
index f19e0513a..1dc257285 100644
--- a/strings/base_meta.h
+++ b/strings/base_meta.h
@@ -117,23 +117,40 @@ namespace winrt::impl
         static constexpr auto data{ category_signature<category_t<T>, T>::data };
     };
 
-#if defined(__clang__)
     template <typename T>
-    struct classic_com_guid
+    struct classic_com_guid_error
     {
-#if __has_declspec_attribute(uuid) && defined(WINRT_IMPL_IUNKNOWN_DEFINED)
-        static constexpr guid value{ __uuidof(T) };
+#ifdef __clang__
+#if !__has_declspec_attribute(uuid)
+        static_assert(std::is_void_v<T> /* dependent_false */, "To use classic COM interfaces, you must compile with -fms-extensions.");
+#endif 
+#endif
+
+#if defined(_MSC_VER) || defined(__clang__)
+#ifndef WINRT_IMPL_IUNKNOWN_DEFINED
+        static_assert(std::is_void_v<T> /* dependent_false */, "To use classic COM interfaces, you must include <unknwn.h> before including C++/WinRT headers.");
+#endif
 #else
-        static_assert(std::is_void_v<T> /* dependent_false */, "To use classic COM interfaces, you must compile with -fms-extensions and include <unknwn.h> before including C++/WinRT headers.");
+        static_assert(std::is_void_v<T> /* dependent_false */, "Classic COM interfaces are not supported with this compiler.");
 #endif
     };
 
     template <typename T>
-    inline constexpr guid guid_v = classic_com_guid<T>::value;
+#ifdef WINRT_IMPL_IUNKNOWN_DEFINED
+#ifdef __clang__
+#if __has_declspec_attribute(uuid)
+    inline constexpr guid guid_v{ __uuidof(T) };
 #else
-    template <typename T>
+    inline constexpr guid guid_v = classic_com_guid_error<T>::value;
+#endif // __has_declspec_attribute(uuid)
+#elif defined(_MSC_VER)
     inline constexpr guid guid_v{ __uuidof(T) };
-#endif
+#else
+    inline constexpr guid guid_v = classic_com_guid_error<T>::value;
+#endif // __clang__
+#else
+    inline constexpr guid guid_v = classic_com_guid_error<T>::value;
+#endif // WINRT_IMPL_IUNKNOWN_DEFINED
 
     template <typename T>
     constexpr auto to_underlying_type(T const value) noexcept

From 16ab08b8761ccd78853dfdf13c8a1de014c43edf Mon Sep 17 00:00:00 2001
From: Charles Milette <charles.milette@gmail.com>
Date: Thu, 6 Oct 2022 19:08:25 -0400
Subject: [PATCH 2/2] Bring back the ability to use guid_v when unknwn.h is
 included after winrt/base.h in MSVC

---
 strings/base_meta.h | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/strings/base_meta.h b/strings/base_meta.h
index 1dc257285..0e800c49f 100644
--- a/strings/base_meta.h
+++ b/strings/base_meta.h
@@ -123,34 +123,28 @@ namespace winrt::impl
 #ifdef __clang__
 #if !__has_declspec_attribute(uuid)
         static_assert(std::is_void_v<T> /* dependent_false */, "To use classic COM interfaces, you must compile with -fms-extensions.");
-#endif 
 #endif
 
-#if defined(_MSC_VER) || defined(__clang__)
 #ifndef WINRT_IMPL_IUNKNOWN_DEFINED
         static_assert(std::is_void_v<T> /* dependent_false */, "To use classic COM interfaces, you must include <unknwn.h> before including C++/WinRT headers.");
 #endif
-#else
+#else // MSVC won't hit this struct, so we can safely assume everything that isn't Clang isn't supported
         static_assert(std::is_void_v<T> /* dependent_false */, "Classic COM interfaces are not supported with this compiler.");
 #endif
     };
 
     template <typename T>
-#ifdef WINRT_IMPL_IUNKNOWN_DEFINED
 #ifdef __clang__
-#if __has_declspec_attribute(uuid)
+#if __has_declspec_attribute(uuid) && defined(WINRT_IMPL_IUNKNOWN_DEFINED)
     inline constexpr guid guid_v{ __uuidof(T) };
 #else
     inline constexpr guid guid_v = classic_com_guid_error<T>::value;
-#endif // __has_declspec_attribute(uuid)
+#endif
 #elif defined(_MSC_VER)
     inline constexpr guid guid_v{ __uuidof(T) };
 #else
     inline constexpr guid guid_v = classic_com_guid_error<T>::value;
-#endif // __clang__
-#else
-    inline constexpr guid guid_v = classic_com_guid_error<T>::value;
-#endif // WINRT_IMPL_IUNKNOWN_DEFINED
+#endif
 
     template <typename T>
     constexpr auto to_underlying_type(T const value) noexcept