include <vector>

namespace ns {
    template <typename T> struct te {};
}

struct st
{
    st(ns::te<int> ar){}
};

void main()
{
    std::vector<st> result;
}

Gives incorrect "qualified name is not allowed -- detected during: -- instantiation of class "std::__1::__is_constructible<, _Tp, _Args...> [with =false, _Tp=std::__1::allocator, _Args=<>]" at line 2072 of "/usr/include/c++/v1/type_traits" -- instantiation of class "std::__1::__is_constructible_void_check<, _Tp, _Args...> [with =false, _Tp=std::__1::allocator, _Args=<>]" at line 2098 of "/usr/include/c++/v1/type_traits" -- instantiation of class "std::__1::is_constructible<_Tp, _Args...> [with _Tp=std::__1::allocator, _Args=<>]" at line 2578 of "/usr/include/c++/v1/type_traits" -- instantiation of class "std::__1::is_nothrow_constructible<_Tp, _Args...> [with _Tp=std::__1::allocator, _Args=<>]" at line 2700 of "/usr/include/c++/v1/type_traits" -- instantiation of class "std::__1::is_nothrow_default_constructible<_Tp> [with _Tp=std::__1::allocator]" at line 507 of "/usr/include/c++/v1/vector" -- instantiation of "std::__1::vector<_Tp, _Allocator>::vector() [with _Tp=st, _Allocator=std::__1::allocator]" at line 14".

compilerPath is "/usr/bin/clang -stdlib=libc++".

Repros on Windows as well when the same headers are used. Doesn't repro with 0.17.6, although it's possible the root cause may have existed and other parser bug fixes were just blocking it in this case?

+1 upvote this if anyone else hits this or cascading errors caused by this.