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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
39 lines
1.5 KiB
C++
39 lines
1.5 KiB
C++
// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -verify -std=c++11 %s
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// Make sure we handle contexts correctly with sizeof
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template<typename T> void f(T n) { // expected-note {{declared here}}
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int buffer[n]; // expected-warning {{variable length arrays in C++ are a Clang extension}} \
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expected-note {{function parameter 'n' with unknown value cannot be used in a constant expression}} \
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expected-note@#instantiate {{in instantiation of function template specialization 'f<int>' requested here}}
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[] { int x = sizeof(sizeof(buffer)); }();
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}
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int main() {
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f<int>(1); // #instantiate
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}
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// Make sure we handle references to non-static data members in unevaluated
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// contexts in class template methods correctly. Previously we assumed these
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// would be valid MemberRefExprs, but they have no 'this' so we need to form a
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// DeclRefExpr to the FieldDecl instead.
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// PR26893
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template <class T>
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struct M {
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M() {}; // expected-note {{in instantiation of default member initializer 'M<S>::m' requested here}}
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int m = *T::x; // expected-error {{invalid use of non-static data member 'x'}}
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void f() {
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// These are valid.
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static_assert(sizeof(T::x) == 8, "ptr");
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static_assert(sizeof(*T::x) == 4, "int");
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}
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};
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struct S { int *x; };
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template struct M<S>; // expected-note {{in instantiation of member function 'M<S>::M' requested here}}
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// Similar test case for PR26893.
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template <typename T=void>
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struct bar {
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struct foo { int array[10]; };
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int baz() { return sizeof(foo::array); }
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};
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template struct bar<>;
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