[libc++] Fix std::make_exception_ptr interaction with ObjC (llvm#135386)

Clang treats throwing/catching ObjC types differently from C++ types,
and omitting the `throw` in `std::make_exception_ptr` breaks ObjC
invariants about how types are thrown/caught.

Fixes llvm#135089

Co-authored-by: Louis Dionne <[email protected]>

Author: itrofimow

libcxx/include/__exception/exception_ptr.h

@@ -15,6 +15,7 @@
 #include <__memory/addressof.h>
 #include <__memory/construct_at.h>
 #include <__type_traits/decay.h>
+#include <__type_traits/is_pointer.h>
 #include <cstdlib>
 #include <typeinfo>
 
@@ -62,7 +63,7 @@ class _LIBCPP_EXPORTED_FROM_ABI exception_ptr {
   static exception_ptr __from_native_exception_pointer(void*) _NOEXCEPT;
 
   template <class _Ep>
-  friend _LIBCPP_HIDE_FROM_ABI exception_ptr make_exception_ptr(_Ep) _NOEXCEPT;
+  friend _LIBCPP_HIDE_FROM_ABI exception_ptr __make_exception_ptr_explicit(_Ep&) _NOEXCEPT;
 
 public:
   // exception_ptr is basically a COW string so it is trivially relocatable.
@@ -91,25 +92,21 @@ class _LIBCPP_EXPORTED_FROM_ABI exception_ptr {
   friend _LIBCPP_EXPORTED_FROM_ABI void rethrow_exception(exception_ptr);
 };
 
-template <class _Ep>
-_LIBCPP_HIDE_FROM_ABI exception_ptr make_exception_ptr(_Ep __e) _NOEXCEPT {
 #  if _LIBCPP_HAS_EXCEPTIONS
-#    if _LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPTION && __cplusplus >= 201103L
+#    if _LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPTION
+template <class _Ep>
+_LIBCPP_HIDE_FROM_ABI exception_ptr __make_exception_ptr_explicit(_Ep& __e) _NOEXCEPT {
   using _Ep2 = __decay_t<_Ep>;
-
   void* __ex = __cxxabiv1::__cxa_allocate_exception(sizeof(_Ep));
 #      ifdef __wasm__
-  // In Wasm, a destructor returns its argument
-  (void)__cxxabiv1::__cxa_init_primary_exception(
-      __ex, const_cast<std::type_info*>(&typeid(_Ep)), [](void* __p) -> void* {
+  auto __cleanup = [](void* __p) -> void* {
+    std::__destroy_at(static_cast<_Ep2*>(__p));
+    return __p;
+  };
 #      else
-  (void)__cxxabiv1::__cxa_init_primary_exception(__ex, const_cast<std::type_info*>(&typeid(_Ep)), [](void* __p) {
-#      endif
-        std::__destroy_at(static_cast<_Ep2*>(__p));
-#      ifdef __wasm__
-        return __p;
+  auto __cleanup = [](void* __p) { std::__destroy_at(static_cast<_Ep2*>(__p)); };
 #      endif
-      });
+  (void)__cxxabiv1::__cxa_init_primary_exception(__ex, const_cast<std::type_info*>(&typeid(_Ep)), __cleanup);
 
   try {
     ::new (__ex) _Ep2(__e);
@@ -118,18 +115,47 @@ _LIBCPP_HIDE_FROM_ABI exception_ptr make_exception_ptr(_Ep __e) _NOEXCEPT {
     __cxxabiv1::__cxa_free_exception(__ex);
     return current_exception();
   }
-#    else
+}
+#    endif
+
+template <class _Ep>
+_LIBCPP_HIDE_FROM_ABI exception_ptr __make_exception_ptr_via_throw(_Ep& __e) _NOEXCEPT {
   try {
     throw __e;
   } catch (...) {
     return current_exception();
   }
+}
+
+template <class _Ep>
+_LIBCPP_HIDE_FROM_ABI exception_ptr make_exception_ptr(_Ep __e) _NOEXCEPT {
+  // Objective-C exceptions are thrown via pointer. When throwing an Objective-C exception,
+  // Clang generates a call to `objc_exception_throw` instead of the usual `__cxa_throw`.
+  // That function creates an exception with a special Objective-C typeinfo instead of
+  // the usual C++ typeinfo, since that is needed to implement the behavior documented
+  // at [1]).
+  //
+  // Because of this special behavior, we can't create an exception via `__cxa_init_primary_exception`
+  // for Objective-C exceptions, otherwise we'd bypass `objc_exception_throw`. See https://llvm.org/PR135089.
+  //
+  // [1]:
+  // https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Exceptions/Articles/Exceptions64Bit.html
+  if _LIBCPP_CONSTEXPR (is_pointer<_Ep>::value) {
+    return std::__make_exception_ptr_via_throw(__e);
+  }
+
+#    if _LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPTION && !defined(_LIBCPP_CXX03_LANG)
+  return std::__make_exception_ptr_explicit(__e);
+#    else
+  return std::__make_exception_ptr_via_throw(__e);
 #    endif
-#  else
-  ((void)__e);
+}
+#  else  // !_LIBCPP_HAS_EXCEPTIONS
+template <class _Ep>
+_LIBCPP_HIDE_FROM_ABI exception_ptr make_exception_ptr(_Ep) _NOEXCEPT {
   std::abort();
-#  endif
 }
+#  endif // _LIBCPP_HAS_EXCEPTIONS
 
 #else // _LIBCPP_ABI_MICROSOFT
 

libcxx/test/std/language.support/support.exception/propagation/make_exception_ptr.objc.pass.mm

@@ -0,0 +1,44 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// This test ensures that we can catch an Objective-C++ exception by type when
+// throwing an exception created via `std::make_exception_ptr`.
+// See http://llvm.org/PR135089.
+
+// UNSUPPORTED: no-exceptions
+// UNSUPPORTED: c++03
+
+// This test requires the Objective-C ARC, which is (only?) available on Darwin
+// out-of-the-box.
+// REQUIRES: has-fobjc-arc && darwin
+
+// ADDITIONAL_COMPILE_FLAGS: -fobjc-arc
+
+#include <cassert>
+#include <exception>
+
+#import <Foundation/Foundation.h>
+
+NSError* RecoverException(const std::exception_ptr& exc) {
+  try {
+    std::rethrow_exception(exc);
+  } catch (NSError* error) {
+    return error;
+  } catch (...) {
+  }
+  return nullptr;
+}
+
+int main(int, char**) {
+  NSError* error         = [NSError errorWithDomain:NSPOSIXErrorDomain code:EPERM userInfo:nil];
+  std::exception_ptr exc = std::make_exception_ptr(error);
+  NSError* recov         = RecoverException(exc);
+  assert(recov != nullptr);
+
+  return 0;
+}