[libc-commits] [libc] [libc] Fix warning on 'extern "C" int main' in test suite (PR #102973)

[Joseph Huber via libc-commits]

https://github.com/jhuber6 updated https://github.com/llvm/llvm-project/pull/102973

>From 272d9dc6f428b321dfab013df7cb0904a1244122 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Mon, 12 Aug 2024 15:36:11 -0500
Subject: [PATCH] [libc] Fix warning on 'extern "C" int main' in test suite

Summary:
According to the C++ standard, The main function shall not be declared
with a linkage-specification. after some changes in
https://github.com/llvm/llvm-project/pull/101853 this started emitting
warnings when building / testing the C library. This source file is
shared with the overlay tests as well as the full build tests. The full
build tests are compiled with `-ffreestanding`, as are all the startup /
integration files. The standard says freestanding environment are all
implementation defined, so this is valid in those cases. This patch
simply prevents adding the linkage when we are compiling unit tests,
which are hosted. This is a continuation on
https://github.com/llvm/llvm-project/pull/102825.
---
 libc/test/UnitTest/LibcTestMain.cpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/libc/test/UnitTest/LibcTestMain.cpp b/libc/test/UnitTest/LibcTestMain.cpp
index 94536e97164686..1025b441c58be4 100644
--- a/libc/test/UnitTest/LibcTestMain.cpp
+++ b/libc/test/UnitTest/LibcTestMain.cpp
@@ -43,7 +43,15 @@ TestOptions parseOptions(int argc, char **argv) {
 
 } // anonymous namespace
 
-extern "C" int main(int argc, char **argv, char **envp) {
+// The C++ standard forbids declaring the main function with a linkage specifier
+// outisde of 'freestanding' mode, only define the linkage for hermetic tests.
+#ifdef __STDC_HOSTED__
+#define TEST_MAIN int main
+#else
+#define TEST_MAIN extern "C" int main
+#endif
+
+TEST_MAIN(int argc, char **argv, char **envp) {
   LIBC_NAMESPACE::testing::argc = argc;
   LIBC_NAMESPACE::testing::argv = argv;
   LIBC_NAMESPACE::testing::envp = envp;