Namespace modules now check version against imported winrt_base

Co-authored-by: Copilot <copilot@github.com>

Author: DefaultRyan

cppwinrt/file_writers.h

@@ -418,7 +418,7 @@ namespace cppwinrt
     {
         writer w;
         write_preamble(w);
-        w.write(strings::base_macros);
+        w.write(strings::base_macros, CPPWINRT_VERSION_STRING);
         w.flush_to_file(settings.output_folder + "winrt/base_macros.h");
     }
 
@@ -486,7 +486,11 @@ namespace cppwinrt
             w.write("import winrt.%;\n", dep);
         }
 
-        w.write("\n");
+        // Version mismatch check: ensure this namespace module was generated by the
+        // same version of cppwinrt.exe as the winrt_base module it imports.
+        // winrt::cppwinrt_version is exported from winrt_base; CPPWINRT_VERSION is
+        // the macro from this module's own base_macros.h in the global module fragment.
+        w.write("\nstatic_assert(winrt::check_version(winrt::cppwinrt_version, CPPWINRT_VERSION), \"Mismatched C++/WinRT headers.\");\n\n");
 
         // Include namespace headers in module purview
         w.write("#include \"winrt/impl/%.0.h\"\n", ns);
@@ -542,7 +546,11 @@ namespace cppwinrt
             w.write("import winrt.%;\n", dep);
         }
 
-        w.write("\n");
+        // Version mismatch check: ensure this namespace module was generated by the
+        // same version of cppwinrt.exe as the winrt_base module it imports.
+        // winrt::cppwinrt_version is exported from winrt_base; CPPWINRT_VERSION is
+        // the macro from this module's own base_macros.h in the global module fragment.
+        w.write("\nstatic_assert(winrt::check_version(winrt::cppwinrt_version, CPPWINRT_VERSION), \"Mismatched C++/WinRT headers.\");\n");
 
         // Forward declarations for all projected types in this SCC.
         // This is required because SCC members have cyclic type references,

strings/base_macros.h

@@ -123,4 +123,11 @@ typedef struct _GUID GUID;
 #define WINRT_IMPL_CONSTEVAL constexpr
 #endif
 
+// CPPWINRT_VERSION is defined here so it is available in module global fragments.
+// In header builds, base_version_odr.h defines it first (before base_macros.h is included),
+// so the #ifndef guard prevents redefinition.
+#ifndef CPPWINRT_VERSION
+#define CPPWINRT_VERSION "%"
+#endif
+
 #endif // WINRT_BASE_MACROS_H

strings/base_module_numerics_ixx.h

@@ -3,6 +3,10 @@
 
 export module winrt_numerics;
 
+#if defined(_MSC_VER)
+#pragma detect_mismatch("C++/WinRT version", CPPWINRT_VERSION)
+#endif
+
 #if __has_include(<windowsnumerics.impl.h>)
 #ifdef _MSC_VER
 #pragma warning(push)

strings/base_version.h

@@ -16,6 +16,8 @@ char const * const WINRT_version = "C++/WinRT version:" CPPWINRT_VERSION;
 
 WINRT_EXPORT namespace winrt
 {
+    inline constexpr char cppwinrt_version[] = CPPWINRT_VERSION;
+
     template <std::size_t BaseSize, std::size_t ComponentSize>
     constexpr bool check_version(char const(&base)[BaseSize], char const(&component)[ComponentSize]) noexcept
     {