Implement P3618R0

Author: kish1n

clang/docs/ReleaseNotes.rst

@@ -135,6 +135,8 @@ C++2c Feature Support
 
 - Implemented `P2719R4 Type-aware allocation and deallocation functions <https://wg21.link/P2719>`_.
 
+- Implemented `P3618R0 Allow attaching main to the global module<https://wg21.link/P3618>`_.
+
 C++23 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1086,7 +1086,7 @@ def ext_main_used : Extension<
     "referring to 'main' within an expression is a Clang extension">, InGroup<Main>;
 def ext_main_invalid_linkage_specification : ExtWarn<
   "'main' should not be "
-  "'extern \"%select{C|C++}0\"'">, InGroup<Main>;
+  "'extern \"C\"'">, InGroup<Main>;
 
 /// parser diagnostics
 def ext_no_declarators : ExtWarn<"declaration does not declare anything">,

clang/lib/Sema/SemaDecl.cpp

@@ -12400,12 +12400,9 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
 
 void Sema::CheckMain(FunctionDecl *FD, const DeclSpec &DS) {
   // [basic.start.main]p3
-  //    The main function shall not be declared with a linkage-specification.
-  if (FD->isExternCContext() ||
-      (FD->isExternCXXContext() &&
-       FD->getDeclContext()->getRedeclContext()->isTranslationUnit()))
-    Diag(FD->getLocation(), diag::ext_main_invalid_linkage_specification)
-        << FD->getLanguageLinkage();
+  //    The main function shall not be declared with C linkage-specification.
+  if (FD->isExternCContext())
+    Diag(FD->getLocation(), diag::ext_main_invalid_linkage_specification);
 
   // C++11 [basic.start.main]p3:
   //   A program that [...] declares main to be inline, static or

clang/test/SemaCXX/modules.cppm

@@ -68,6 +68,8 @@ int n;
 //--- test3.cpp
 export module bar;
 
+extern "C++" int main() {}
+
 static int m;
 
 int n;

libcxx/utils/libcxx/test/features.py

@@ -340,7 +340,7 @@ def _mingwSupportsModules(cfg):
             cfg,
             """
             export module test;
-            int main(int, char**) { return 0; }
+            extern "C++" int main(int, char**) { return 0; }
           """,
         ),
     ),