WINRT_SOURCE_LOCATION has ODR checks that prevent mixing cpp17 and cpp20 static libraries

strings/base_macros.h

@@ -77,14 +77,53 @@ struct IUnknown;
 typedef struct _GUID GUID;
 #endif
 
-// std::source_location is a C++20 feature, which is above the C++17 feature floor for cppwinrt.  The source location needs
-// to be the calling code, not cppwinrt itself, so that it is useful to developers building on top of this library.  As a
-// result any public-facing method that can result in an error needs a default-constructed source_location argument.  Because
-// this type does not exist in C++17 we need to use a macro to optionally add parameters and forwarding wherever appropriate.
+#if defined(__cpp_consteval)
+#define WINRT_IMPL_CONSTEVAL consteval
+#else
+#define WINRT_IMPL_CONSTEVAL constexpr
+#endif
+
+// The intrinsics (such as __builtin_FILE()) that power std::source_location are also used to power winrt:impl::slim_source_location.
+// The source location needs to be for the calling code, not cppwinrt itself, so that it is useful to developers building on top of
+// this library.  As a result any public-facing method that can result in an error needs a default-constructed slim_source_location
+// argument so that it will collect source information from the application code that is calling into cppwinrt.
 //
-// Some projects may decide to disable std::source_location support to prevent source code information from ending up in their
-// release binaries, or to reduce binary size.  Defining WINRT_NO_SOURCE_LOCATION will prevent this feature from activating.
-#if defined(__cpp_lib_source_location) && !defined(WINRT_NO_SOURCE_LOCATION)
+// We do not directly use std::source_location for two reasons:
+//  1) std::source_location::function_name() is unavoidable.  These strings end up in the final binary, bloating their size.  This
+//     is particularly impactful for code bases that use templates heavily.  Cases of 50% binary size growth have been observed.
+//  2) std::source_location is a cpp20 feature, which is above the cpp17 feature floor for cppwinrt.  By defining our own version
+//     we can avoid ODR violations in mixed cpp17/cpp20 builds.  cpp17 callers will have an ABI that matches cpp20 callers (they
+//     will just not have useful file/line/function information).
+//
+// Some projects may decide that the source information binary size impact is not worth the benefit.  Defining WINRT_NO_SOURCE_LOCATION
+// will prevent this feature from activating.  The slim_source_location type will be forwarded around but it will not include any
+// nonzero data.  That eliminates the biggest source of binary size overhead.
+//
+// To help with debugging the __builtin_FUNCTION() intrinsic will be used in _DEBUG builds.  This will provide a bit more diagnostic
+// value at the cost of binary size.  The assumption is that binary size is considered less important in debug builds so this tradeoff
+// is acceptable.
+
+#if !defined(__cpp_lib_source_location)
+// cpp17 mode.  The source_location intrinsics are not available.
+#define WINRT_IMPL_BUILTIN_LINE 0
+#define WINRT_IMPL_BUILTIN_FILE nullptr
+#define WINRT_IMPL_BUILTIN_FUNCTION nullptr
+#elif defined(WINRT_NO_SOURCE_LOCATION)
+// The caller has disabled source_location support.  Ensure that there is no binary size overhead for line/file/function.
+#define WINRT_IMPL_BUILTIN_LINE 0
+#define WINRT_IMPL_BUILTIN_FILE nullptr
+#define WINRT_IMPL_BUILTIN_FUNCTION nullptr
+#elif _DEBUG
+// Debug builds include FUNCTION information, which has a heavy binary size impact.
+#define WINRT_IMPL_BUILTIN_LINE __builtin_LINE()
+#define WINRT_IMPL_BUILTIN_FILE __builtin_FILE()
+#define WINRT_IMPL_BUILTIN_FUNCTION __builtin_FUNCTION()
+#else
+// Release builds in cpp20 mode get file and line information.
+#define WINRT_IMPL_BUILTIN_LINE __builtin_LINE()
+#define WINRT_IMPL_BUILTIN_FILE __builtin_FILE()
+#define WINRT_IMPL_BUILTIN_FUNCTION nullptr
+#endif
 
 namespace winrt::impl
 {
@@ -93,19 +132,23 @@ namespace winrt::impl
     // have heavy binary size overhead when templates cause many permutations to exist.
     struct slim_source_location
     {
-        [[nodiscard]] static consteval slim_source_location current(
-            const std::uint_least32_t line = __builtin_LINE(),
-            const char* const file = __builtin_FILE()) noexcept
+        [[nodiscard]] static WINRT_IMPL_CONSTEVAL slim_source_location current(
+            const std::uint_least32_t line = WINRT_IMPL_BUILTIN_LINE,
+            const char* const file = WINRT_IMPL_BUILTIN_FILE,
+            const char* const function = WINRT_IMPL_BUILTIN_FUNCTION) noexcept
         {
-            return slim_source_location{ line, file };
+            return slim_source_location{ line, file, function };
         }
 
         [[nodiscard]] constexpr slim_source_location() noexcept = default;
 
-        [[nodiscard]] constexpr slim_source_location(const std::uint_least32_t line,
-            const char* const file) noexcept :
+        [[nodiscard]] constexpr slim_source_location(
+            const std::uint_least32_t line,
+            const char* const file,
+            const char* const function) noexcept :
             m_line(line),
-            m_file(file)
+            m_file(file),
+            m_function(function)
         {}
 
         [[nodiscard]] constexpr std::uint_least32_t line() const noexcept
@@ -118,39 +161,18 @@ namespace winrt::impl
             return m_file;
         }
 
-        constexpr const char* function_name() const noexcept
+        [[nodiscard]] constexpr const char* function_name() const noexcept
         {
-            // This is intentionally not included.  See comment above.
-            return nullptr;
+            return m_function;
         }
 
     private:
         const std::uint_least32_t m_line{};
         const char* const m_file{};
+        const char* const m_function{};
     };
 }
 
-// std::source_location includes function_name which can be helpful but creates a lot of binary size impact.  Many consumers
-// have defined WINRT_NO_SOURCE_LOCATION to prevent this impact, losing the value of source_location.  We have defined a
-// slim_source_location struct that is equivalent but excludes function_name.  This should have the vast majority of the
-// usefulness of source_location while having a much smaller binary impact.
-//
-// When building _DEBUG binary size is not usually much of a concern, so we can use the full source_location type.
-#ifdef _DEBUG
-#define WINRT_IMPL_SOURCE_LOCATION_ARGS_NO_DEFAULT , std::source_location const& sourceInformation
-#define WINRT_IMPL_SOURCE_LOCATION_ARGS , std::source_location const& sourceInformation = std::source_location::current()
-#define WINRT_IMPL_SOURCE_LOCATION_ARGS_SINGLE_PARAM std::source_location const& sourceInformation = std::source_location::current()
-
-#define WINRT_IMPL_SOURCE_LOCATION_FORWARD , sourceInformation
-#define WINRT_IMPL_SOURCE_LOCATION_FORWARD_SINGLE_PARAM sourceInformation
-
-#define WINRT_SOURCE_LOCATION_ACTIVE
-
-#ifdef _MSC_VER
-#pragma detect_mismatch("WINRT_SOURCE_LOCATION", "true")
-#endif // _MSC_VER
-
-#else // !_DEBUG
 #define WINRT_IMPL_SOURCE_LOCATION_ARGS_NO_DEFAULT , winrt::impl::slim_source_location const& sourceInformation
 #define WINRT_IMPL_SOURCE_LOCATION_ARGS , winrt::impl::slim_source_location const& sourceInformation = winrt::impl::slim_source_location::current()
 #define WINRT_IMPL_SOURCE_LOCATION_ARGS_SINGLE_PARAM winrt::impl::slim_source_location const& sourceInformation = winrt::impl::slim_source_location::current()
@@ -163,18 +185,3 @@ namespace winrt::impl
 #ifdef _MSC_VER
 #pragma detect_mismatch("WINRT_SOURCE_LOCATION", "slim")
 #endif // _MSC_VER
-
-#endif // _DEBUG
-
-#else
-#define WINRT_IMPL_SOURCE_LOCATION_ARGS_NO_DEFAULT
-#define WINRT_IMPL_SOURCE_LOCATION_ARGS
-#define WINRT_IMPL_SOURCE_LOCATION_ARGS_SINGLE_PARAM
-
-#define WINRT_IMPL_SOURCE_LOCATION_FORWARD
-#define WINRT_IMPL_SOURCE_LOCATION_FORWARD_SINGLE_PARAM
-
-#ifdef _MSC_VER
-#pragma detect_mismatch("WINRT_SOURCE_LOCATION", "false")
-#endif //  _MSC_VER
-#endif // defined(__cpp_lib_source_location) && !defined(WINRT_NO_SOURCE_LOCATION)