From 193f458c30106b114b81cb7b2d21de41099f5191 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2@gmail.com>
Date: Fri, 13 May 2022 16:13:54 -0400
Subject: [PATCH] [libc++] Remove overly conservative error in <stdatomic.h>

As mentionned in D97044, it is fine if users include <atomic> and then
include <stdatomic.h> -- we don't need to error out for that case.

Differential Revision: https://reviews.llvm.org/D125579
---
 libcxx/include/stdatomic.h                         |  7 -------
 .../incompatible_with_stdatomic.verify.cpp         |  6 +++---
 .../incompatible_with_atomic.verify.cpp            | 22 ----------------------
 3 files changed, 3 insertions(+), 32 deletions(-)
 delete mode 100644 libcxx/test/libcxx/atomics/stdatomic.h.syn/incompatible_with_atomic.verify.cpp

diff --git a/libcxx/include/stdatomic.h b/libcxx/include/stdatomic.h
index 8495504..d9550c4 100644
--- a/libcxx/include/stdatomic.h
+++ b/libcxx/include/stdatomic.h
@@ -226,14 +226,7 @@ using std::atomic_thread_fence _LIBCPP_USING_IF_EXISTS;
 // the header. We do this because Clang has historically shipped a <stdatomic.h>
 // header that would be available in all Standard modes, and we don't want to
 // break that use case.
-//
-// However, if the user has already used <atomic> before, the two headers are
-// incompatible before C++23, so we issue a clear error here to avoid obscure
-// issues down the line.
 # if __has_include_next(<stdatomic.h>)
-#   ifdef _LIBCPP_ATOMIC
-#     error <stdatomic.h> is incompatible with <atomic> before C++23. Please compile with -std=c++23.
-#   endif
 #   include_next <stdatomic.h>
 # endif
 
diff --git a/libcxx/test/libcxx/atomics/atomics.syn/incompatible_with_stdatomic.verify.cpp b/libcxx/test/libcxx/atomics/atomics.syn/incompatible_with_stdatomic.verify.cpp
index 49bc2dcc..a8d56c5 100644
--- a/libcxx/test/libcxx/atomics/atomics.syn/incompatible_with_stdatomic.verify.cpp
+++ b/libcxx/test/libcxx/atomics/atomics.syn/incompatible_with_stdatomic.verify.cpp
@@ -9,9 +9,9 @@
 // UNSUPPORTED: libcpp-has-no-threads
 // REQUIRES: c++03 || c++11 || c++14 || c++17 || c++20
 
-// This test ensures that we issue a reasonable diagnostic when using <atomic> while <stdatomic.h>
-// is in use too. Before C++23, this otherwise leads to obscure errors because <atomic> may try
-// to redefine things defined by <stdatomic.h>.
+// This test ensures that we issue a reasonable diagnostic when including <atomic> after
+// <stdatomic.h> has been included. Before C++23, this otherwise leads to obscure errors
+// because <atomic> may try to redefine things defined by <stdatomic.h>.
 
 // Ignore additional weird errors that happen when the two headers are mixed.
 // ADDITIONAL_COMPILE_FLAGS: -Xclang -verify-ignore-unexpected=error -Xclang -verify-ignore-unexpected=warning
diff --git a/libcxx/test/libcxx/atomics/stdatomic.h.syn/incompatible_with_atomic.verify.cpp b/libcxx/test/libcxx/atomics/stdatomic.h.syn/incompatible_with_atomic.verify.cpp
deleted file mode 100644
index ff4124a..0000000
--- a/libcxx/test/libcxx/atomics/stdatomic.h.syn/incompatible_with_atomic.verify.cpp
+++ /dev/null
@@ -1,22 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// 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
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: libcpp-has-no-threads
-// REQUIRES: c++03 || c++11 || c++14 || c++17 || c++20
-
-// This test ensures that we issue a reasonable diagnostic when using <stdatomic.h> while <atomic>
-// is in use too. Before C++23, this otherwise leads to obscure errors because <stdatomic.h> tries
-// to redefine things defined by <atomic>.
-
-// Ignore additional weird errors that happen when the two headers are mixed.
-// ADDITIONAL_COMPILE_FLAGS: -Xclang -verify-ignore-unexpected=error -Xclang -verify-ignore-unexpected=warning
-
-#include <atomic>
-#include <stdatomic.h>
-
-// expected-error@*:* {{<stdatomic.h> is incompatible with <atomic> before C++23}}
-- 
2.7.4