[Potential Bug] [MSVC] Exporting views from a module causes error unless the importer also includes the view's headers

[alessiocali]

Hello! Please forgive me if this turns out to be an MSVC bug, or a module bug (I know modules are still somewhat experimental). I'm at my wits ends and I would like to ask the community for guidance.

So in my pet project (which is built using C++20 modules) I'm wrapping range-v3 in some commodity classes that I plan to use to have a controlled interface. The problem is that whenever I try to use the iterator from range-v3 to iterate over my wrapper class I start getting all sorts of compilation error.

My exact example is much more complex than this but it gives a generic compiler error from MSVC which is not very useful. Instead here is a very stripped down example where I try to directly return the range-v3 view.

// view.ixx
module;
#define _HAS_EXCEPTIONS 0
#include <range/v3/view/transform.hpp>
#include <vector>

export module View;
export namespace tptest
{
    auto GetDoubleView(std::vector<int>& v)
    {
        return v | ranges::views::transform([](const int& val) { return 2 * val; });
    }
}

// main.cpp
#define _HAS_EXCEPTIONS 0
#include <iostream>
#include <vector>

import View;
int main()
{
    const std::vector<int> vals = { 1, 2, 3 };
    for (const auto& x : tptest::GetDoubleView(vals))
    {
        std::cout << x << std::endl;
    }
}

Compile with

cl /std:c++20 /Irange-v3/include /c view.ixx
cl /std:c++20 /Irange-v3/include main.cpp view.obj

Gets me the following output

C:\Development\Cpp\range-module-compiler-error\range-v3\include\range\v3\functional\bind_back.hpp(89): error C2079: 'ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,tptest::GetDoubleView::<lambda_1>>::tuple_t::fn_' uses undefined struct 'ranges::views::transform_base_fn'
C:\Development\Cpp\range-module-compiler-error\range-v3\include\range\v3\functional\bind_back.hpp(92): note: see reference to class template instantiation 'ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,tptest::GetDoubleView::<lambda_1>>::tuple_t' being compiled
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.33.31629\include\type_traits(1456): note: see reference to class template instantiation 'ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,tptest::GetDoubleView::<lambda_1>>' being compiled
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.33.31629\include\type_traits(1677): note: see reference to alias template instantiation 'std::_Decltype_invoke_nonzero<ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,tptest::GetDoubleView::<lambda_1>>,std::vector<int,std::allocator<int>>&,>' being compiled
C:\Development\Cpp\range-module-compiler-error\range-v3\include\range\v3\functional\concepts.hpp(35): note: see reference to variable template 'const bool is_invocable_v<ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,`tptest::GetDoubleView'::`2'::<lambda_1> >,std::vector<int,std::allocator<int> > &>' being compiled
C:\Development\Cpp\range-module-compiler-error\range-v3\include\range\v3\view\view.hpp(84): note: see reference to variable template 'const bool invocable<ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,`tptest::GetDoubleView'::`2'::<lambda_1> >,std::vector<int,std::allocator<int> > &>' being compiled
C:\Development\Cpp\range-module-compiler-error\range-v3\include\range\v3\view\view.hpp(116): note: see reference to variable template 'const bool invocable_view_closure<ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,`tptest::GetDoubleView'::`2'::<lambda_1> >,std::vector<int,std::allocator<int> > &>' being compiled
main.cpp(11): fatal error C1116: unrecoverable error importing module 'View'.  Specialization of 'ranges::views::view_closure_base_ns::operator |' with arguments 'std::vector<int,std::allocator<int>>&, ranges::detail::bind_back_fn_<ranges::views::transform_base_fn,tptest::GetDoubleView::<lambda_1>>'

From a cursory glance it seems like a failed import. In theory, #include-ing a header in the global module unit should make it visible to the importer, and in fact I did a few experiments where I did exactly that and it worked fine. But in the case of Range-V3 something seems to go amiss. In fact, just adding #include <range/v3/view/transform.hpp> to main.cpp is enough to make the compilation succeed and get me the output I want.

Thoughts? Suggestions? Should I just forward this to the Visual Studio team?

[alessiocali]

Might be related to #1595