https://github.com/ashwinbanwari created https://github.com/llvm/llvm-project/pull/146635
Revival of https://github.com/llvm/llvm-project/pull/146247. Now that https://github.com/llvm/llvm-project/pull/146461 is merged to allow `extern "C++"` for main, we can merge this change. >From 76bd9279c0410fa53c8a8ca34229f5ca3a4812e3 Mon Sep 17 00:00:00 2001 From: Ashwin Banwari <ashwinkbanw...@gmail.com> Date: Mon, 30 Jun 2025 18:10:24 -0700 Subject: [PATCH 1/2] Reapply "[clang] [modules] Add err_main_in_named_module (#146247)" This reverts commit 8a5b97a7205db189ca82f44dec7a399c2b5da546. --- clang/docs/ReleaseNotes.rst | 3 +++ clang/include/clang/Basic/DiagnosticSemaKinds.td | 4 ++++ clang/lib/Sema/SemaDecl.cpp | 8 ++++++++ clang/test/Driver/autocomplete.c | 1 + clang/test/SemaCXX/modules.cppm | 2 ++ 5 files changed, 18 insertions(+) diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index e6c8f9df22170..db99cc9233377 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -659,6 +659,9 @@ Improvements to Clang's diagnostics diagnostics when floating-point numbers had both width field and plus or space prefix specified. (#GH143951) +- A warning is now emitted when ``main`` is attached to a named module, + which can be turned off with ``-Wno-main-attached-to-named-module``. (#GH146247) + - Clang now avoids issuing `-Wreturn-type` warnings in some cases where the final statement of a non-void function is a `throw` expression, or a call to a function that is trivially known to always throw (i.e., its diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td index 5062505cf3c01..451619709c087 100644 --- a/clang/include/clang/Basic/DiagnosticSemaKinds.td +++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td @@ -1062,6 +1062,10 @@ def err_constexpr_main : Error< "'main' is not allowed to be declared %select{constexpr|consteval}0">; def err_deleted_main : Error<"'main' is not allowed to be deleted">; def err_mainlike_template_decl : Error<"%0 cannot be a template">; +def warn_main_in_named_module + : ExtWarn<"'main' should not be attached to a named module; consider " + "adding C++ language linkage">, + InGroup<DiagGroup<"main-attached-to-named-module">>; def err_main_returns_nonint : Error<"'main' must return 'int'">; def ext_main_returns_nonint : ExtWarn<"return type of 'main' is not 'int'">, InGroup<MainReturnType>; diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp index a34e2c9cbb003..f4bc191d1dae6 100644 --- a/clang/lib/Sema/SemaDecl.cpp +++ b/clang/lib/Sema/SemaDecl.cpp @@ -12489,6 +12489,14 @@ void Sema::CheckMain(FunctionDecl *FD, const DeclSpec &DS) { : FixItHint()); FD->setInvalidDecl(true); } + + // In C++ [basic.start.main]p3, it is said a program attaching main to a + // named module is ill-formed. + if (FD->isInNamedModule()) { + const SourceLocation start = FD->getTypeSpecStartLoc(); + Diag(start, diag::warn_main_in_named_module) + << FixItHint::CreateInsertion(start, "extern \"C++\" ", true); + } } // Treat protoless main() as nullary. diff --git a/clang/test/Driver/autocomplete.c b/clang/test/Driver/autocomplete.c index 8cc604dbff875..4983b71496834 100644 --- a/clang/test/Driver/autocomplete.c +++ b/clang/test/Driver/autocomplete.c @@ -111,6 +111,7 @@ // RUN: %clang --autocomplete=-Wma | FileCheck %s -check-prefix=WARNING // WARNING: -Wmacro-redefined // WARNING-NEXT: -Wmain +// WARNING-NEXT: -Wmain-attached-to-named-module // WARNING-NEXT: -Wmain-return-type // WARNING-NEXT: -Wmalformed-warning-check // WARNING-NEXT: -Wmany-braces-around-scalar-init diff --git a/clang/test/SemaCXX/modules.cppm b/clang/test/SemaCXX/modules.cppm index 5d0d6da44a2ed..81bc749c58259 100644 --- a/clang/test/SemaCXX/modules.cppm +++ b/clang/test/SemaCXX/modules.cppm @@ -68,6 +68,8 @@ int n; //--- test3.cpp export module bar; +int main() {} // expected-warning {{'main' should not be attached to a named module; consider adding C++ language linkage}} + static int m; int n; >From 195b81a312fed2b13bea14666feb45f3c1f599ed Mon Sep 17 00:00:00 2001 From: Ashwin Banwari <ashwinkbanw...@gmail.com> Date: Tue, 1 Jul 2025 22:33:55 -0700 Subject: [PATCH 2/2] update test --- clang/test/SemaCXX/modules.cppm | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/clang/test/SemaCXX/modules.cppm b/clang/test/SemaCXX/modules.cppm index 5d7ea6bacf7e0..5e0b3be9870c7 100644 --- a/clang/test/SemaCXX/modules.cppm +++ b/clang/test/SemaCXX/modules.cppm @@ -41,6 +41,8 @@ struct S { export static int n; // expected-error {{expected member name or ';'}} }; +int main() {} // expected-warning {{'main' should not be attached to a named module; consider adding C++ language linkage}} + // FIXME: Exports of declarations without external linkage are disallowed. // Exports of declarations with non-external-linkage types are disallowed. @@ -68,8 +70,6 @@ int n; //--- test3.cpp export module bar; -int main() {} // expected-warning {{'main' should not be attached to a named module; consider adding C++ language linkage}} - extern "C++" int main() {} static int m; _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
