[libcxx-dev] Commit implementing LWG 2510 (r372777) breaks compilation of LLVM

[Ilya Biryukov via libcxx-dev]

Hi Louis,

I'm seeing compilation failures while trying to compile clang with libc++
after r372777.
This is blocking our integrates.

Checking for implicitly default-constructible types results in errors
coming from access-checking.
I would expect this shouldn't happen, given that the check is done in
SFINAE context.
Is there a quick workaround? Should we revert the change until it's found?

Here is the compilation error itself:

.../include/c++/v1/type_traits:2820:110: error: calling a protected
constructor of class 'clang::ento::Loc'
struct __is_implicitly_default_constructible<_Tp,
decltype(__test_implicit_default_constructible<_Tp const&>({}))>

                                 ^
.../include/c++/v1/utility:350:18: note: in instantiation of template class
'std::__u::__is_implicitly_default_constructible<clang::ento::Loc, void>'
requested here
          return __is_implicitly_default_constructible<_U1>::value
                 ^
.../include/c++/v1/utility:341:19: note: in instantiation of function
template specialization 'std::__u::pair<clang::ento::Loc,
clang::ento::SVal>::_CheckArgs::__enable_implicit_default<clang::ento::Loc,
clang::ento::SVal>' requested here
              && !__enable_implicit_default<_U1, _U2>();
                  ^
.../include/c++/v1/utility:403:45: note: in instantiation of function
template specialization 'std::__u::pair<clang::ento::Loc,
clang::ento::SVal>::_CheckArgs::__enable_explicit_default<clang::ento::Loc,
clang::ento::SVal>' requested here
            _CheckArgsDep<_Dummy>::template __enable_explicit_default<_T1,
_T2>()
                                            ^
.../include/c++/v1/utility:406:5: note: while substituting prior template
arguments into non-type template parameter [with _Dummy = true]
    pair() _NOEXCEPT_(is_nothrow_default_constructible<first_type>::value &&
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/c++/v1/utility:297:29: note: while substituting deduced template
arguments into function template 'pair' [with _Dummy = (no value), $1 = (no
value)]
struct _LIBCPP_TEMPLATE_VIS pair
                            ^
third_party/llvm/llvm/include/llvm/Support/type_traits.h:90:7: note:
(skipping 3 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see
all)
union trivial_helper {
      ^
third_party/llvm/llvm/include/llvm/Support/type_traits.h:176:40: note: in
instantiation of static data member
'llvm::is_trivially_copyable<std::__u::pair<clang::ento::Loc,
clang::ento::SVal> >::has_trivial_move_constructor' requested here
      (has_deleted_move_constructor || has_trivial_move_constructor) &&
                                       ^
third_party/llvm/llvm/include/llvm/ADT/SmallVector.h:178:56: note: in
instantiation of static data member
'llvm::is_trivially_copyable<std::__u::pair<clang::ento::Loc,
clang::ento::SVal> >::value' requested here
template <typename T, bool = is_trivially_copyable<T>::value>
                                                       ^
third_party/llvm/llvm/include/llvm/ADT/SmallVector.h:315:32: note: in
instantiation of default argument for
'SmallVectorTemplateBase<std::__u::pair<clang::ento::Loc,
clang::ento::SVal> >' required here
class SmallVectorImpl : public SmallVectorTemplateBase<T> {
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~
third_party/llvm/llvm/include/llvm/ADT/SmallVector.h:837:28: note: in
instantiation of template class
'llvm::SmallVectorImpl<std::__u::pair<clang::ento::Loc, clang::ento::SVal>
>' requested here
class SmallVector : public SmallVectorImpl<T>, SmallVectorStorage<T, N> {
                           ^
third_party/llvm/llvm/tools/clang/lib/StaticAnalyzer/Core/Store.cpp:51:46:
note: in instantiation of template class
'llvm::SmallVector<std::__u::pair<clang::ento::Loc, clang::ento::SVal>,
16>' requested here
  SmallVector<CallEvent::FrameBindingTy, 16> InitialBindings;
                                             ^
third_party/llvm/llvm/tools/clang/include/clang/StaticAnalyzer/Core/PathSensitive/SVals.h:322:3:
note: declared protected here
  Loc() = default;

-- 
Regards,
Ilya Biryukov
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