[Bug]: Clang++ compilation error

[wingfiring]

Description

Failed to build the following code (works with clang++ on other platforms)

#include <tuple>
#include <type_traits>

struct Foo{
    int v = 42;
    template<typename T> Foo& operator=(T ) 
        noexcept(std::is_nothrow_move_assignable<T>::value) {
        return *this;
    }
};

int main(){
    std::tuple<Foo> a, b;
    std::swap(a, b);
}

Save the above code to file a.cpp.
With command line:

~/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang++ -std=c++17 a.cpp --target=aarch64-none-linux-android28 --sysroot=$HOME/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot  -ftemplate-back
trace-limit=0 

Got error messages (modified to hide sensitive info):

In file included from a.cpp:1:
In file included from /Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/tuple:149:
In file included from /Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/__tuple:15:
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:3493:71: error: exception specification of 'operator=<std::__tuple_leaf<0, Foo, false>>' uses itself
    : public integral_constant<bool, __is_nothrow_assignable(_Tp, _Arg)> {};
                                                                      ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:3493:71: note: in instantiation of exception specification for 'operator=<std::__tuple_leaf<0, Foo, false>>' requested here
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:3540:14: note: in instantiation of template class 'std::is_nothrow_assignable<std::__tuple_leaf<0, Foo, false> &, std::__tuple_leaf<0, Foo, false> &&>' requested here
    : public is_nothrow_assignable<typename add_lvalue_reference<_Tp>::type,
             ^
a.cpp:9:59: note: in instantiation of template class 'std::is_nothrow_move_assignable<std::__tuple_leaf<0, Foo, false>>' requested here
    template<typename T> Foo& operator=(T ) noexcept(std::is_nothrow_move_assignable<T>::value)
                                                          ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:3493:71: note: in instantiation of exception specification for 'operator=<std::__tuple_leaf<0, Foo, false>>' requested here
    : public integral_constant<bool, __is_nothrow_assignable(_Tp, _Arg)> {};
                                                                      ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/tuple:263:42: note: in instantiation of template class 'std::is_nothrow_assignable<Foo &, std::__tuple_leaf<0, Foo, false>>' requested here
        operator=(_Tp&& __t) _NOEXCEPT_((is_nothrow_assignable<_Hp&, _Tp>::value))
                                         ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:2447:83: note: in instantiation of exception specification for 'operator=<std::__tuple_leaf<0, Foo, false>>' requested here
struct _LIBCPP_TEMPLATE_VIS is_assignable : _BoolConstant<__is_assignable(_Tp, _Up)> { };
                                                                                  ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:2501:14: note: in instantiation of template class 'std::is_assignable<std::__tuple_leaf<0, Foo, false> &, std::__tuple_leaf<0, Foo, false> &&>' requested here
    : public is_assignable<typename add_lvalue_reference<_Tp>::type,
             ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:4041:5: note: in instantiation of template class 'std::is_move_assignable<std::__tuple_leaf<0, Foo, false>>' requested here
    is_move_assignable<_Tp>::value
    ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:4099:21: note: while substituting deduced template arguments into function template 'swap' [with _Tp = std::__tuple_leaf<0, Foo, false>]
    static decltype(swap(_VSTD::declval<_LHS>(), _VSTD::declval<_RHS>()))
                    ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:4105:23: note: while substituting explicitly-specified template arguments into function template '__test_swap'
    typedef decltype((__test_swap<_Tp, _Up>(0))) __swap1;
                      ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:4115:57: note: in instantiation of template class 'std::__detail::__swappable_with<std::__tuple_leaf<0, Foo, false> &, std::__tuple_leaf<0, Foo, false> &, true>' requested here
template <class _Tp, class _Up = _Tp, bool _Swappable = __swappable_with<_Tp, _Up>::value>
                                                        ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/type_traits:4139:48: note: in instantiation of default argument for '__nothrow_swappable_with<std::__tuple_leaf<0, Foo, false> &, std::__tuple_leaf<0, Foo, false> &>' required here
    : public integral_constant<bool, __detail::__nothrow_swappable_with<_Tp&>::value>
                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/tuple:270:44: note: in instantiation of template class 'std::__is_nothrow_swappable<std::__tuple_leaf<0, Foo, false>>' requested here
    int swap(__tuple_leaf& __t) _NOEXCEPT_(__is_nothrow_swappable<__tuple_leaf>::value)
                                           ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/tuple:470:45: note: in instantiation of exception specification for 'swap' requested here
        __swallow(__tuple_leaf<_Indx, _Tp>::swap(static_cast<__tuple_leaf<_Indx, _Tp>&>(__t))...);
                                            ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/tuple:954:18: note: in instantiation of member function 'std::__tuple_impl<std::__tuple_indices<0>, Foo>::swap' requested here
        {__base_.swap(__t.__base_);}
                 ^
/Users/someone/Library/Android/sdk/ndk/25.2.9519653/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/include/c++/v1/tuple:1001:10: note: in instantiation of member function 'std::tuple<Foo>::swap' requested here
    {__t.swap(__u);}
         ^
a.cpp:19:10: note: in instantiation of function template specialization 'std::swap<Foo>' requested here
    std::swap(a, b);
         ^
1 error generated.

Upstream bug

No response

Commit to cherry-pick

No response

Affected versions

r25

Canary version

No response

Host OS

Mac

Host OS version

MacOS 12.6.7

Affected ABIs

arm64-v8a

[DanAlbert]

This definitely looks like #1530. Test case compiles fine with r26 beta 1.

I did have to remove the -ftemplate-back argument which is not recognized. I also removed the sysroot argument which at best does nothing.

[wingfiring]

yes, just verified in r26 beta 1, it's fixed.
Thanks for your help.