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

[Louis Dionne via libcxx-dev]

I was able to reproduce the failure. I don't understand it yet but it looks
like we might have exposed a Clang bug. FWIW, here's the repro:

#include <utility>
#include <type_traits>

struct Base { };
struct Derived : Base { protected: Derived() = default; };
static_assert(!std::is_default_constructible<std::pair<Derived, int>
>::value, "");


Louis

On Wed, Sep 25, 2019 at 5:18 AM Ilya Biryukov <ibiryukov at google.com> wrote:

> Reverted in r372832.
>
> On Wed, Sep 25, 2019 at 11:00 AM Ilya Biryukov <ibiryukov at google.com>
> wrote:
>
>> I'll have to revert the change to unbreak our integrate.
>> Sorry about the inconvenience.
>>
>>
>> On Wed, Sep 25, 2019 at 10:41 AM Ilya Biryukov <ibiryukov at google.com>
>> wrote:
>>
>>> 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
>>>
>>
>>
>> --
>> Regards,
>> Ilya Biryukov
>>
>
>
> --
> Regards,
> Ilya Biryukov
>
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