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The alias-declaration of decltype lambda is broken in the for loop #63627

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hewillk opened this issue Jun 30, 2023 · 4 comments
Closed

The alias-declaration of decltype lambda is broken in the for loop #63627

hewillk opened this issue Jun 30, 2023 · 4 comments
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clang:frontend Language frontend issues, e.g. anything involving "Sema" confirmed Verified by a second party

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@hewillk
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hewillk commented Jun 30, 2023

Clang accepts the following invalid code.

template<class T>
void f() {
  for (using U = decltype([]{}.operator----); 
       auto x : "abc") { }
};

int main() {
  f<int>();
}

https://godbolt.org/z/dTKbnv3nE
@EugeneZelenko EugeneZelenko added clang:frontend Language frontend issues, e.g. anything involving "Sema" and removed new issue labels Jun 30, 2023
@llvmbot
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llvmbot commented Jun 30, 2023

@llvm/issue-subscribers-clang-frontend

@shafik
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shafik commented Jun 30, 2023 •
edited
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If we attempt to use the type we crash: https://godbolt.org/z/KdaYW8r3h

In the non-templated case we obtain the correct diagnostic: https://godbolt.org/z/5orxWsfEc

@shafik shafik added the confirmed Verified by a second party label Jun 30, 2023
@cor3ntin
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cor3ntin commented Jul 5, 2023

https://reviews.llvm.org/D154492 This ended up a pretty bad bug, we did not preserve the using declaration in a using statement, at all . So when doing a TreeTransform, there was nothing to transform.

The fact this was found by fuzzing is pretty funny to me :D

@cor3ntin
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Fixed!

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@cor3ntin @shafik @EugeneZelenko @llvmbot @hewillk