[libcxx-commits] [libcxx] [libc++] Introduce ABI sensitive areas to avoid requiring _LIBCPP_HIDE_FROM_ABI everywhere (PR #131156)

[Louis Dionne via libcxx-commits]

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@@ -577,12 +577,25 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_POP_EXTENSION_DIAGNOSTICS
 #  endif
 
-// Inline namespaces are available in Clang/GCC/MSVC regardless of C++ dialect.
 // clang-format off
-#  define _LIBCPP_BEGIN_NAMESPACE_STD _LIBCPP_PUSH_EXTENSION_DIAGNOSTICS                                               \
-                                      namespace _LIBCPP_TYPE_VISIBILITY_DEFAULT std {                                  \
+#  define _LIBCPP_BEGIN_HIDE_FROM_ABI                                                                                  \
+    _LIBCPP_DIAGNOSTIC_PUSH                                                                                            \
+    _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wpragma-clang-attribute")                                                       \
+    _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wignored-attributes")                                                           \
+    _Pragma(_LIBCPP_TOSTRING(clang attribute _LibcxxHideFromABI.push(__attribute__((                                   \
+                __exclude_from_explicit_instantiation__, __abi_tag__(_LIBCPP_TOSTRING(_LIBCPP_ODR_SIGNATURE)))),       \
+            apply_to = function)))                                                                                     \
+    _LIBCPP_DIAGNOSTIC_POP
+#  define _LIBCPP_END_HIDE_FROM_ABI _Pragma("clang attribute _LibcxxHideFromABI.pop")
+
+#  define _LIBCPP_BEGIN_ABI_SENSITIVE _LIBCPP_END_HIDE_FROM_ABI
+#  define _LIBCPP_END_ABI_SENSITIVE _LIBCPP_BEGIN_HIDE_FROM_ABI
+
+// Inline namespaces are available in Clang/GCC/MSVC regardless of C++ dialect.
+#  define _LIBCPP_BEGIN_NAMESPACE_STD _LIBCPP_PUSH_EXTENSION_DIAGNOSTICS _LIBCPP_BEGIN_HIDE_FROM_ABI                   \
+                                      namespace _LIBCPP_TYPE_VISIBILITY_DEFAULT _LIBCPP_HIDDEN std {                   \
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ldionne wrote:

Why is `_LIBCPP_HIDDEN` required here? That seems surprising.

Answer: that's because we can't apply visibility attributes with the pragma push/pop, so we need to do it by applying the visibility attribute on the namespace.

https://github.com/llvm/llvm-project/pull/131156