[clang]improve diagnosing redefined defaulted constructor with different exception specs (#69688)

      |               ~~~~~~~~~^~~~~~~~

- Clang now always diagnoses when using non-standard layout types in ``offsetof`` .

  (`#64619: <https://github.com/llvm/llvm-project/issues/64619>`_)

- Clang now diagnoses redefined defaulted constructor when redefined

  defaulted constructor with different exception specs.

  (`#69094: <https://github.com/llvm/llvm-project/issues/69094>`_)

- Clang now diagnoses use of variable-length arrays in C++ by default (and

  under ``-Wall`` in GNU++ mode). This is an extension supported by Clang and

  GCC, but is very easy to accidentally use without realizing it's a

  }

  if (getLangOpts().CPlusPlus) {

    // C++1z [over.load]p2

    //   Certain function declarations cannot be overloaded:

    //     -- Function declarations that differ only in the return type,

    //        the exception specification, or both cannot be overloaded.

    // Check the exception specifications match. This may recompute the type of

    // both Old and New if it resolved exception specifications, so grab the

    // types again after this. Because this updates the type, we do this before

    // any of the other checks below, which may update the "de facto" NewQType

    // but do not necessarily update the type of New.

    if (CheckEquivalentExceptionSpec(Old, New))

      return true;

    OldQType = Context.getCanonicalType(Old->getType());

    NewQType = Context.getCanonicalType(New->getType());

      }

    }

    // C++1z [over.load]p2

    //   Certain function declarations cannot be overloaded:

    //     -- Function declarations that differ only in the return type,

    //        the exception specification, or both cannot be overloaded.

    // Check the exception specifications match. This may recompute the type of

    // both Old and New if it resolved exception specifications, so grab the

    // types again after this. Because this updates the type, we do this before

    // any of the other checks below, which may update the "de facto" NewQType

    // but do not necessarily update the type of New.

    if (CheckEquivalentExceptionSpec(Old, New))

      return true;

    // C++11 [dcl.attr.noreturn]p1:

    //   The first declaration of a function shall specify the noreturn

    //   attribute if any declaration of that function specifies the noreturn

// RUN: %clang_cc1 -fsyntax-only -verify -fcxx-exceptions -std=c++11 %s

struct ExplicitlySpecialMethod {

  ExplicitlySpecialMethod() = default;

};

ExplicitlySpecialMethod::ExplicitlySpecialMethod() {} // expected-error{{definition of explicitly defaulted default constructor}}

struct ImplicitlySpecialMethod {};

ImplicitlySpecialMethod::ImplicitlySpecialMethod() {} // expected-error{{definition of implicitly declared default constructor}}