84a3aadf0f
Reapplication of 7339c0f782d5c70e0928f8991b0c05338a90c84c with a fix for a crash involving arrays without a size expression. Clang supports VLAs in C++ as an extension, but we currently only warn on their use when you pass -Wvla, -Wvla-extension, or -pedantic. However, VLAs as they're expressed in C have been considered by WG21 and rejected, are easy to use accidentally to the surprise of users (e.g., https://ddanilov.me/default-non-standard-features/), and they have potential security implications beyond constant-size arrays (https://wiki.sei.cmu.edu/confluence/display/c/ARR32-C.+Ensure+size+arguments+for+variable+length+arrays+are+in+a+valid+range). C++ users should strongly consider using other functionality such as std::vector instead. This seems like sufficiently compelling evidence to warn users about VLA use by default in C++ modes. This patch enables the -Wvla-extension diagnostic group in C++ language modes by default, and adds the warning group to -Wall in GNU++ language modes. The warning is still opt-in in C language modes, where support for VLAs is somewhat less surprising to users. RFC: https://discourse.llvm.org/t/rfc-diagnosing-use-of-vlas-in-c/73109 Fixes https://github.com/llvm/llvm-project/issues/62836 Differential Revision: https://reviews.llvm.org/D156565
68 lines
2.0 KiB
C++
68 lines
2.0 KiB
C++
// RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify %s
|
|
// RUN: %clang_cc1 -fsyntax-only -std=c++1y -verify %s -DCXX1Y
|
|
|
|
#ifndef CXX1Y
|
|
|
|
template<typename T, typename U, U> using alias_ref = T;
|
|
template<typename T, typename U, U> void func_ref() {}
|
|
template<typename T, typename U, U> struct class_ref {};
|
|
|
|
template<int N>
|
|
struct U {
|
|
static int a;
|
|
};
|
|
|
|
template<int N> struct S; // expected-note 6{{here}}
|
|
|
|
template<int N>
|
|
int U<N>::a = S<N>::kError; // expected-error 6{{undefined}}
|
|
|
|
template<typename T>
|
|
void f() {
|
|
(void)alias_ref<int, int&, U<0>::a>(); // expected-note {{here}}
|
|
(void)func_ref<int, int&, U<1>::a>(); // expected-note {{here}}
|
|
(void)class_ref<int, int&, U<2>::a>(); // expected-note {{here}}
|
|
};
|
|
|
|
template<typename T>
|
|
void not_instantiated() {
|
|
// These cases (arguably) do not require instantiation of U<i>::a.
|
|
(void)alias_ref<int, int&, U<3>::a>();
|
|
(void)func_ref<int, int&, U<4>::a>();
|
|
(void)class_ref<int, int&, U<5>::a>();
|
|
};
|
|
|
|
template<int N>
|
|
void fi() {
|
|
(void)alias_ref<int, int&, U<N>::a>(); // expected-note {{here}}
|
|
(void)func_ref<int, int&, U<N+1>::a>(); // expected-note {{here}}
|
|
(void)class_ref<int, int&, U<N+2>::a>(); // expected-note {{here}}
|
|
};
|
|
|
|
int main() {
|
|
f<int>(); // expected-note 3{{here}}
|
|
fi<10>(); // expected-note 3{{here}}
|
|
}
|
|
|
|
namespace N {
|
|
template<typename T> struct S { static int n; }; // expected-note {{declared here}}
|
|
template<typename T> int S<T>::n = 5;
|
|
void g(int*);
|
|
template<typename T> int f() {
|
|
int k[S<T>::n]; // expected-warning {{variable length arrays in C++ are a Clang extension}} \
|
|
expected-note {{read of non-const variable 'n' is not allowed in a constant expression}}
|
|
g(k);
|
|
return k[3];
|
|
}
|
|
int j = f<int>(); // expected-note {{in instantiation of function template specialization 'N::f<int>' requested here}}
|
|
}
|
|
|
|
#else
|
|
|
|
namespace { template<typename> extern int n; }
|
|
template<typename T> int g() { return n<int>; }
|
|
namespace { extern template int n<int>; } // expected-error {{explicit instantiation declaration of 'n<int>' with internal linkage}}
|
|
|
|
#endif
|
|
|