From aae025a948f73e428846c7fa60ada5c4d9ef80cc Mon Sep 17 00:00:00 2001
From: Ben Deane <ben@elbeno.com>
Date: Tue, 31 Dec 2024 14:40:33 -0700
Subject: [PATCH] :sparkles: Add `flatten` attribute

---
 include/stdx/compiler.hpp | 12 ++++++++++++
 test/CMakeLists.txt       |  1 +
 test/compiler.cpp         | 15 +++++++++++++++
 3 files changed, 28 insertions(+)
 create mode 100644 test/compiler.cpp

diff --git a/include/stdx/compiler.hpp b/include/stdx/compiler.hpp
index 80760d7..05e723a 100644
--- a/include/stdx/compiler.hpp
+++ b/include/stdx/compiler.hpp
@@ -22,6 +22,14 @@
 #endif
 #endif
 
+#ifndef USING_ATTR_NS
+#if defined(__clang__)
+#define USING_ATTR_NS using clang:
+#else
+#define USING_ATTR_NS using gnu:
+#endif
+#endif
+
 #ifndef ALWAYS_INLINE
 #define ALWAYS_INLINE inline __attribute__((always_inline))
 #endif
@@ -30,6 +38,10 @@
 #define NEVER_INLINE __attribute__((noinline))
 #endif
 
+#ifndef FLATTEN
+#define FLATTEN __attribute__((flatten))
+#endif
+
 #ifndef MUSTTAIL
 #if defined(__clang__)
 #define MUSTTAIL [[clang::musttail]]
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 5d71cc8..6cf74f2 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -31,6 +31,7 @@ add_tests(
     byterator
     cached
     callable
+    compiler
     concepts
     conditional
     ct_conversions
diff --git a/test/compiler.cpp b/test/compiler.cpp
new file mode 100644
index 0000000..1ac18b7
--- /dev/null
+++ b/test/compiler.cpp
@@ -0,0 +1,15 @@
+#include <stdx/compiler.hpp>
+
+#include <catch2/catch_test_macros.hpp>
+
+TEST_CASE("using attribute namespace", "[compiler]") {
+    [[USING_ATTR_NS warn_unused_result]] auto f(int) -> int;
+}
+
+ALWAYS_INLINE auto f1(int) -> void;
+
+TEST_CASE("NEVER_INLINE", "[compiler]") { NEVER_INLINE auto f2(int) -> void; }
+
+TEST_CASE("FLATTEN", "[compiler]") { FLATTEN auto f3(int) -> void; }
+
+ALWAYS_INLINE FLATTEN auto f4(int) -> void;