[libc++] Make __libcpp_verbose_abort [[noreturn]]

[ldionne]

Summary

This will allow using it in functions that are [[noreturn]] themselves.

[ldionne]

Make backdeployment implementation [[noreturn]]

libcxx/include/__verbose_abort

 // We can't provide a great implementation because it needs to be pretty much
 // dependency-free (this is included everywhere else in the library).
 #if defined(_LIBCPP_HAS_NO_VERBOSE_ABORT_IN_LIBRARY) && !defined(_LIBCPP_AVAILABILITY_CUSTOM_VERBOSE_ABORT_PROVIDED)
 
 extern "C" void abort();
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-_LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) _LIBCPP_HIDE_FROM_ABI inline
+_LIBCPP_NORETURN _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) _LIBCPP_HIDE_FROM_ABI inline
 void __libcpp_verbose_abort(const char *, ...) {
-    ::abort();
+  __builtin_unreachable(); // never reached, but needed to tell the compiler that the function never returns
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
 #else
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-_LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2)
+_LIBCPP_NORETURN _LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2)
 void __libcpp_verbose_abort(const char *__format, ...);
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif
 
 #endif // _LIBCPP___VERBOSE_ABORT

libcxx/test/libcxx/assertions/customize_verbose_abort.backdeployment.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 // Make sure that we can enable assertions when we back-deploy to older platforms
 // if we define _LIBCPP_AVAILABILITY_CUSTOM_VERBOSE_ABORT_PROVIDED.
 //
-// Note that this test isn't really different from customize_handler.pass.cpp when
-// run outside of back-deployment scenarios, but we still run it all the time.
+// Note that this test isn't really different from customize_verbose_abort.pass.cpp when
+// run outside of back-deployment scenarios, but we always want to run this test.
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_ASSERTIONS=1 -D_LIBCPP_AVAILABILITY_CUSTOM_VERBOSE_ABORT_PROVIDED
 
-#include <cassert>
+#include <cstdlib>
 
-bool handler_called = false;
 void std::__libcpp_verbose_abort(char const*, ...) {
-  handler_called = true;
+  std::exit(EXIT_SUCCESS);
 }
 
 int main(int, char**) {
   _LIBCPP_ASSERT(false, "message");
-  assert(handler_called);
-  return 0;
+  return EXIT_FAILURE;
 }

libcxx/test/libcxx/assertions/customize_verbose_abort.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 // Test that we can set a custom verbose termination function.
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_ASSERTIONS=1
 
 // We flag uses of the verbose termination function in older dylibs at compile-time to avoid runtime
 // failures when back-deploying.
 // XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0|12.0}}
 
-#include <cassert>
+#include <cstdlib>
 
-bool handler_called = false;
 void std::__libcpp_verbose_abort(char const*, ...) {
-  handler_called = true;
+  std::exit(EXIT_SUCCESS);
 }
 
 int main(int, char**) {
   _LIBCPP_ASSERT(false, "message");
-  assert(handler_called);
-  return 0;
+  return EXIT_FAILURE;
 }

libcxx/test/libcxx/assertions/debug_mode_compatibility.pass.cpp

 // it to enable assertions previously.
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEBUG=0
 
 // We flag uses of the assertion handler in older dylibs at compile-time to avoid runtime
 // failures when back-deploying.
 // XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0|12.0}}
 
-#include <cassert>
+#include <cstdlib>
 
-bool handler_called = false;
 void std::__libcpp_verbose_abort(char const*, ...) {
-  handler_called = true;
+  std::exit(EXIT_SUCCESS);
 }
 
 int main(int, char**) {
   _LIBCPP_ASSERT(false, "message");
-  assert(handler_called);
-  return 0;
+  return EXIT_FAILURE;
 }