From 93fc20d91cb409d32000efe0774b1b3d150eeee9 Mon Sep 17 00:00:00 2001 From: Davide Italiano Date: Fri, 14 Aug 2015 14:13:29 +0000 Subject: [PATCH] [Sema] main can't be declared as global variable, in C++. So, we now reject that. We also warn for any external-linkage global variable named main in C, because it results in undefined behavior. PR: 24309 Differential Revision: http://reviews.llvm.org/D11658 Reviewed by: rsmith git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@245051 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/clang/Basic/DiagnosticSemaKinds.td | 4 ++ lib/Sema/SemaDecl.cpp | 16 +++++ .../basic/basic.start/basic.start.main/p3.cpp | 66 +++++++++++++++++++ test/Sema/warn-extern-main.c | 56 ++++++++++++++++ 4 files changed, 142 insertions(+) create mode 100644 test/CXX/basic/basic.start/basic.start.main/p3.cpp create mode 100644 test/Sema/warn-extern-main.c diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td index b672394c4f..680443ab23 100644 --- a/include/clang/Basic/DiagnosticSemaKinds.td +++ b/include/clang/Basic/DiagnosticSemaKinds.td @@ -510,6 +510,10 @@ def warn_main_one_arg : Warning<"only one parameter on 'main' declaration">, def err_main_arg_wrong : Error<"%select{first|second|third|fourth}0 " "parameter of 'main' (%select{argument count|argument array|environment|" "platform-specific data}0) must be of type %1">; +def err_main_global_variable : + Error<"main cannot be declared as global variable">; +def warn_main_redefined : Warning<"variable named 'main' with external linkage " + "has undefined behavior">, InGroup
; def ext_main_used : Extension< "ISO C++ does not allow 'main' to be used by a program">, InGroup
; diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp index 7c54986f56..c3fdd900cd 100644 --- a/lib/Sema/SemaDecl.cpp +++ b/lib/Sema/SemaDecl.cpp @@ -6111,6 +6111,22 @@ Sema::ActOnVariableDeclarator(Scope *S, Declarator &D, DeclContext *DC, } } + // Special handling of variable named 'main'. + if (Name.isIdentifier() && Name.getAsIdentifierInfo()->isStr("main") && + NewVD->getDeclContext()->getRedeclContext()->isTranslationUnit() && + !getLangOpts().Freestanding && !NewVD->getDescribedVarTemplate()) { + + // C++ [basic.start.main]p3 + // A program that declares a variable main at global scope is ill-formed. + if (getLangOpts().CPlusPlus) + Diag(D.getLocStart(), diag::err_main_global_variable); + + // In C, and external-linkage variable named main results in undefined + // behavior. + else if (NewVD->hasExternalFormalLinkage()) + Diag(D.getLocStart(), diag::warn_main_redefined); + } + if (D.isRedeclaration() && !Previous.empty()) { checkDLLAttributeRedeclaration( *this, dyn_cast(Previous.getRepresentativeDecl()), NewVD, diff --git a/test/CXX/basic/basic.start/basic.start.main/p3.cpp b/test/CXX/basic/basic.start/basic.start.main/p3.cpp new file mode 100644 index 0000000000..f7085ca31d --- /dev/null +++ b/test/CXX/basic/basic.start/basic.start.main/p3.cpp @@ -0,0 +1,66 @@ +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST1 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST2 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST3 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST4 +// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++14 -DTEST5 +// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++14 -DTEST6 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST7 +// 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 + +#if TEST1 +int main; // expected-error{{main cannot be declared as global variable}} + +#elif TEST2 +// expected-no-diagnostics +int f () { + int main; + return main; +} + +#elif TEST3 +// expected-no-diagnostics +void x(int main) {}; +int y(int main); + +#elif TEST4 +// expected-no-diagnostics +class A { + static int main; +}; + +#elif TEST5 +// expected-no-diagnostics +template constexpr T main; + +#elif TEST6 +extern template constexpr T main; //expected-error{{expected unqualified-id}} + +#elif TEST7 +// expected-no-diagnostics +namespace foo { + int main; +} + +#elif TEST8 +void z(void) +{ + extern int main; // expected-error{{main cannot be declared as global variable}} +} + +#elif TEST9 +// expected-no-diagnostics +int q(void) +{ + static int main; + return main; +} + +#elif TEST10 +// expected-no-diagnostics +int main; + +#else +#error Unknown Test +#endif diff --git a/test/Sema/warn-extern-main.c b/test/Sema/warn-extern-main.c new file mode 100644 index 0000000000..62c2c9b4a8 --- /dev/null +++ b/test/Sema/warn-extern-main.c @@ -0,0 +1,56 @@ +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST1 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST2 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST3 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST4 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST5 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST6 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST7 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST8 +// RUN: %clang_cc1 -fsyntax-only -verify %s -DTEST9 -ffreestanding + +#if TEST1 +int main; // expected-warning{{variable named 'main' with external linkage has undefined behavior}} + +#elif TEST2 +extern int main; // expected-warning{{variable named 'main' with external linkage has undefined behavior}} + +#elif TEST3 +// expected-no-diagnostics +void x() { + static int main; +} + +#elif TEST4 +void x() { + extern int main; // expected-warning{{variable named 'main' with external linkage has undefined behavior}} +} + +#elif TEST5 +// expected-no-diagnostics +void x() { + int main; +} + +#elif TEST6 +// expected-no-diagnostics +static int main; + +#elif TEST7 +// expected-no-diagnostics +void x() { + auto int main; +} + +#elif TEST8 +// expected-no-diagnostics +void x() { + register int main; +} + +#elif TEST9 +// expected-no-diagnostics +int main; + +#else +#error Unknown Test +#endif -- 2.40.0