[libc++] Use availability to rely on key functions for bad_expected_access and bad_function_call (#87390)

This patch uses our availability machinery to allow defining a key
function for bad_function_call and bad_expected_access at all times but
only rely on it when we can. This prevents compilers from complaining
about weak vtables and reduces code bloat and the amount of work done by
the dynamic linker.

rdar://111917845

3 files changed, 14 insertions, 2 deletions

diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
index 208500e..a4a3fee 100644
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -10,6 +10,7 @@ set(LIBCXX_SOURCES
   chrono.cpp
   error_category.cpp
   exception.cpp
+  expected.cpp
   filesystem/filesystem_clock.cpp
   filesystem/filesystem_error.cpp
   filesystem/path_parser.h
diff --git a/libcxx/src/expected.cpp b/libcxx/src/expected.cpp
new file mode 100644
index 0000000..f30efb5
--- /dev/null
+++ b/libcxx/src/expected.cpp
@@ -0,0 +1,13 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <expected>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+const char* bad_expected_access<void>::what() const noexcept { return "bad access to std::expected"; }
+_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/src/functional.cpp b/libcxx/src/functional.cpp
index 570bb78..ef53e3e 100644
--- a/libcxx/src/functional.cpp
+++ b/libcxx/src/functional.cpp
@@ -10,9 +10,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifdef _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
 bad_function_call::~bad_function_call() noexcept {}
-#endif
 
 #ifdef _LIBCPP_ABI_BAD_FUNCTION_CALL_GOOD_WHAT_MESSAGE
 const char* bad_function_call::what() const noexcept { return "std::bad_function_call"; }