[clang] [libcxx] [clang] [modules] Implement P3618R0: Allow attaching main to the global module (PR #146461)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Ashwin Banwari (ashwinbanwari)

<details>
<summary>Changes</summary>

Remove the prior warning for attaching extern "C++" to main.

---
Full diff: https://github.com/llvm/llvm-project/pull/146461.diff


5 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+2) 
- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+1-1) 
- (modified) clang/lib/Sema/SemaDecl.cpp (+3-6) 
- (modified) clang/test/SemaCXX/modules.cppm (+2) 
- (modified) libcxx/utils/libcxx/test/features.py (+1-1) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index e6c8f9df22170..33dd07179aeea 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/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
 ^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 5062505cf3c01..d5d982d20eaa5 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/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">,
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index a34e2c9cbb003..61b82b8377e22 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/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
diff --git a/clang/test/SemaCXX/modules.cppm b/clang/test/SemaCXX/modules.cppm
index 5d0d6da44a2ed..ddbbc7cd86360 100644
--- a/clang/test/SemaCXX/modules.cppm
+++ b/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;
diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
index 74746e37d3bc4..a479ea48ac810 100644
--- a/libcxx/utils/libcxx/test/features.py
+++ b/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; }
           """,
         ),
     ),

``````````

</details>


https://github.com/llvm/llvm-project/pull/146461