[clang] [Clang] strengthen checks for 'main' function to meet [basic.start.main] p3 requirements (PR #101853)
Oleksandr T. via cfe-commits
cfe-commits at lists.llvm.org
Tue Aug 6 09:45:51 PDT 2024
https://github.com/a-tarasyuk updated https://github.com/llvm/llvm-project/pull/101853
>From 56c8d3a8e5f860ec1f68adf997d502849de1cb50 Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Sun, 4 Aug 2024 00:45:49 +0300
Subject: [PATCH 1/3] [Clang] strengthen checks for 'main' function to meet
[basic.start.main] p3 requirements
---
clang/docs/ReleaseNotes.rst | 2 +
.../clang/Basic/DiagnosticSemaKinds.td | 3 +
clang/lib/AST/Decl.cpp | 8 +--
clang/lib/Sema/SemaDecl.cpp | 28 +++++++--
.../basic/basic.start/basic.start.main/p3.cpp | 61 +++++++++++++++++++
5 files changed, 91 insertions(+), 11 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 4c7bd099420ab..ad5fe7d96d6cb 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -145,6 +145,8 @@ Improvements to Clang's diagnostics
- -Wdangling-assignment-gsl is enabled by default.
+- Clang now diagnoses the use of `main` in an `extern` context as invalid according to [basic.start.main] p3. Fixes #GH101512.
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 581434d33c5c9..37920ce6a2fed 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -990,6 +990,9 @@ def warn_main_redefined : Warning<"variable named 'main' with external linkage "
"has undefined behavior">, InGroup<Main>;
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>;
/// parser diagnostics
def ext_no_declarators : ExtWarn<"declaration does not declare anything">,
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 490c4a2fc525c..9bf2ee680073b 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -3292,11 +3292,9 @@ bool FunctionDecl::isImmediateFunction() const {
}
bool FunctionDecl::isMain() const {
- const TranslationUnitDecl *tunit =
- dyn_cast<TranslationUnitDecl>(getDeclContext()->getRedeclContext());
- return tunit &&
- !tunit->getASTContext().getLangOpts().Freestanding &&
- isNamed(this, "main");
+ const DeclContext *DC = getDeclContext();
+ return isNamed(this, "main") && !getLangOpts().Freestanding &&
+ (DC->getRedeclContext()->isTranslationUnit() || isExternC());
}
bool FunctionDecl::isMSVCRTEntryPoint() const {
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 4fea38d1b02a9..613126e9423fd 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7353,6 +7353,15 @@ void emitReadOnlyPlacementAttrWarning(Sema &S, const VarDecl *VD) {
}
}
+// Checks if VD is declared at global scope or with C language linkage
+static bool isMainVar(DeclarationName Name, VarDecl *VD) {
+ return Name.getAsIdentifierInfo() &&
+ Name.getAsIdentifierInfo()->isStr("main") &&
+ !VD->getDescribedVarTemplate() &&
+ (VD->getDeclContext()->getRedeclContext()->isTranslationUnit() ||
+ VD->isExternC());
+}
+
NamedDecl *Sema::ActOnVariableDeclarator(
Scope *S, Declarator &D, DeclContext *DC, TypeSourceInfo *TInfo,
LookupResult &Previous, MultiTemplateParamsArg TemplateParamLists,
@@ -8052,10 +8061,7 @@ NamedDecl *Sema::ActOnVariableDeclarator(
}
// Special handling of variable named 'main'.
- if (Name.getAsIdentifierInfo() && Name.getAsIdentifierInfo()->isStr("main") &&
- NewVD->getDeclContext()->getRedeclContext()->isTranslationUnit() &&
- !getLangOpts().Freestanding && !NewVD->getDescribedVarTemplate()) {
-
+ if (!getLangOpts().Freestanding && isMainVar(Name, NewVD)) {
// C++ [basic.start.main]p3
// A program that declares a variable main at global scope is ill-formed.
if (getLangOpts().CPlusPlus)
@@ -12210,7 +12216,18 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
return Redeclaration;
}
-void Sema::CheckMain(FunctionDecl* FD, const DeclSpec& DS) {
+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();
+ FD->setInvalidDecl();
+ return;
+ }
+
// C++11 [basic.start.main]p3:
// A program that [...] declares main to be inline, static or
// constexpr is ill-formed.
@@ -12238,7 +12255,6 @@ void Sema::CheckMain(FunctionDecl* FD, const DeclSpec& DS) {
<< FixItHint::CreateRemoval(DS.getConstexprSpecLoc());
FD->setConstexprKind(ConstexprSpecKind::Unspecified);
}
-
if (getLangOpts().OpenCL) {
Diag(FD->getLocation(), diag::err_opencl_no_main)
<< FD->hasAttr<OpenCLKernelAttr>();
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
index f7085ca31d6c9..6e98af81ea9a8 100644
--- a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
@@ -8,6 +8,9 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST8
// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST9
// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST10 -ffreestanding
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s -DTEST11
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s -DTEST12
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s -DTEST13
#if TEST1
int main; // expected-error{{main cannot be declared as global variable}}
@@ -61,6 +64,64 @@ int q(void)
// expected-no-diagnostics
int main;
+#elif TEST11
+extern "C" {
+ namespace Y {
+ int main; // expected-error {{main cannot be declared as global variable}}
+ }
+}
+namespace ns {
+ extern "C" int main; // expected-error {{main cannot be declared as global variable}}
+}
+
+#elif TEST12
+extern "C" struct A { int main(); }; // ok
+
+namespace c {
+ extern "C" void main(); // expected-error {{'main' should not be 'extern "C"'}}
+}
+
+extern "C" {
+ namespace Z {
+ void main(); // expected-error {{'main' should not be 'extern "C"'}}
+ }
+}
+
+namespace ns {
+ extern "C" struct A {
+ int main; // ok
+ };
+
+ extern "C" struct B {
+ int main(); // ok
+ };
+}
+
+#elif TEST13
+extern "C++" {
+ int main(); // expected-error {{'main' should not be 'extern "C++"'}}
+}
+
+extern "C" {
+ int main(); // expected-error {{'main' should not be 'extern "C"'}}
+}
+
+extern "C" int main(); // expected-error {{'main' should not be 'extern "C"'}}
+extern "C++" int main(); // expected-error {{'main' should not be 'extern "C++"'}}
+
+namespace ns1 {
+ extern "C++" int main(); // ok
+ extern "C" {
+ extern "C++" {
+ int main(void *); // ok
+ }
+ }
+}
+
+namespace ns2 {
+ extern "C++" void main() {} // ok
+}
+
#else
#error Unknown Test
#endif
>From 87f5b9c319ce7c476afde7743b9c56c547f6b2dc Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Tue, 6 Aug 2024 18:59:19 +0300
Subject: [PATCH 2/3] fix typo. use -pedantic instead of -pedantic-errors
---
clang/lib/Sema/SemaDecl.cpp | 2 +-
.../basic/basic.start/basic.start.main/p3.cpp | 18 +++++++++---------
2 files changed, 10 insertions(+), 10 deletions(-)
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 613126e9423fd..9103e65eb4bce 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7353,7 +7353,7 @@ void emitReadOnlyPlacementAttrWarning(Sema &S, const VarDecl *VD) {
}
}
-// Checks if VD is declared at global scope or with C language linkage
+// Checks if VD is declared at global scope or with C language linkage.
static bool isMainVar(DeclarationName Name, VarDecl *VD) {
return Name.getAsIdentifierInfo() &&
Name.getAsIdentifierInfo()->isStr("main") &&
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
index 6e98af81ea9a8..9fbbdc72651e4 100644
--- a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
@@ -8,9 +8,9 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST8
// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST9
// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST10 -ffreestanding
-// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s -DTEST11
-// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s -DTEST12
-// RUN: %clang_cc1 -fsyntax-only -verify -pedantic-errors %s -DTEST13
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST11
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST12
+// RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST13
#if TEST1
int main; // expected-error{{main cannot be declared as global variable}}
@@ -78,12 +78,12 @@ namespace ns {
extern "C" struct A { int main(); }; // ok
namespace c {
- extern "C" void main(); // expected-error {{'main' should not be 'extern "C"'}}
+ extern "C" void main(); // expected-warning {{'main' should not be 'extern "C"'}}
}
extern "C" {
namespace Z {
- void main(); // expected-error {{'main' should not be 'extern "C"'}}
+ void main(); // expected-warning {{'main' should not be 'extern "C"'}}
}
}
@@ -99,15 +99,15 @@ namespace ns {
#elif TEST13
extern "C++" {
- int main(); // expected-error {{'main' should not be 'extern "C++"'}}
+ int main(); // expected-warning {{'main' should not be 'extern "C++"'}}
}
extern "C" {
- int main(); // expected-error {{'main' should not be 'extern "C"'}}
+ int main(); // expected-warning {{'main' should not be 'extern "C"'}}
}
-extern "C" int main(); // expected-error {{'main' should not be 'extern "C"'}}
-extern "C++" int main(); // expected-error {{'main' should not be 'extern "C++"'}}
+extern "C" int main(); // expected-warning {{'main' should not be 'extern "C"'}}
+extern "C++" int main(); // expected-warning {{'main' should not be 'extern "C++"'}}
namespace ns1 {
extern "C++" int main(); // ok
>From 41583815b688c7283414124f30d7c186a46dd89c Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk at outlook.com>
Date: Tue, 6 Aug 2024 19:45:32 +0300
Subject: [PATCH 3/3] update diagnostics and add additional comments
---
clang/include/clang/Basic/DiagnosticSemaKinds.td | 2 +-
clang/lib/Sema/SemaDecl.cpp | 11 ++++++++---
.../CXX/basic/basic.start/basic.start.main/p3.cpp | 8 ++++----
3 files changed, 13 insertions(+), 8 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 37920ce6a2fed..ecbe7fa2cf76d 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -985,7 +985,7 @@ def err_main_arg_wrong : Error<"%select{first|second|third|fourth}0 "
def warn_main_returns_bool_literal : Warning<"bool literal returned from "
"'main'">, InGroup<Main>;
def err_main_global_variable :
- Error<"main cannot be declared as global variable">;
+ Error<"main cannot be declared as a variable %select{in the global scope|with C language linkage}0">;
def warn_main_redefined : Warning<"variable named 'main' with external linkage "
"has undefined behavior">, InGroup<Main>;
def ext_main_used : Extension<
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 9103e65eb4bce..e6a6efe1d72d6 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -8062,10 +8062,14 @@ NamedDecl *Sema::ActOnVariableDeclarator(
// Special handling of variable named 'main'.
if (!getLangOpts().Freestanding && isMainVar(Name, NewVD)) {
- // C++ [basic.start.main]p3
- // A program that declares a variable main at global scope is ill-formed.
+ // C++ [basic.start.main]p3:
+ // A program that declares
+ // - a variable main at global scope, or
+ // - an entity named main with C language linkage (in any namespace)
+ // is ill-formed
if (getLangOpts().CPlusPlus)
- Diag(D.getBeginLoc(), diag::err_main_global_variable);
+ Diag(D.getBeginLoc(), diag::err_main_global_variable)
+ << NewVD->isExternC();
// In C, and external-linkage variable named main results in undefined
// behavior.
@@ -12255,6 +12259,7 @@ void Sema::CheckMain(FunctionDecl *FD, const DeclSpec &DS) {
<< FixItHint::CreateRemoval(DS.getConstexprSpecLoc());
FD->setConstexprKind(ConstexprSpecKind::Unspecified);
}
+
if (getLangOpts().OpenCL) {
Diag(FD->getLocation(), diag::err_opencl_no_main)
<< FD->hasAttr<OpenCLKernelAttr>();
diff --git a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
index 9fbbdc72651e4..d23d00ccdeebc 100644
--- a/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
+++ b/clang/test/CXX/basic/basic.start/basic.start.main/p3.cpp
@@ -13,7 +13,7 @@
// RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s -DTEST13
#if TEST1
-int main; // expected-error{{main cannot be declared as global variable}}
+int main; // expected-error{{main cannot be declared as a variable in the global scope}}
#elif TEST2
// expected-no-diagnostics
@@ -49,7 +49,7 @@ namespace foo {
#elif TEST8
void z(void)
{
- extern int main; // expected-error{{main cannot be declared as global variable}}
+ extern int main; // expected-error{{main cannot be declared as a variable in the global scope}}}
}
#elif TEST9
@@ -67,11 +67,11 @@ int main;
#elif TEST11
extern "C" {
namespace Y {
- int main; // expected-error {{main cannot be declared as global variable}}
+ int main; // expected-error {{main cannot be declared as a variable with C language linkage}}}
}
}
namespace ns {
- extern "C" int main; // expected-error {{main cannot be declared as global variable}}
+ extern "C" int main; // expected-error {{main cannot be declared as a variable with C language linkage}}
}
#elif TEST12
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