Applied LLVM-47414 workaround to std::ranges::join_view

[AnabelSMRuggiero]

When piping into std::views::join, Clang eagerly instantiates the join_view::_InnerRng template alias. This alias is used in the requirements of the resulting view's const qualified begin() and end() methods. This check is performed and causes a hard compile error even if the source contains no calls to the const qualified methods.

I used the workaround applied to the same methods of std::views::transform_view.

A simplified reproduction of code that fails to compile under Clang can be found here. Piping a filter_view or a view composed on top of a filter_view will cause this erroneous compile error; filter_view has no const qualified overloads of begin() and end().

[ghost]

All CLA requirements met.

[CaseyCarter]

The fix looks great, but we're missing a regression test. Could you please add your minimal repro as a test case in tests/std/tests/P0896R4_views_join/test.cpp?

[AnabelSMRuggiero]

I added most of the requested changes in a new branch of my fork.
I wanted to delay pushing the changes to my main branch while waiting for a confirmation about whether to maintain consistency with the transform_view workaround. Figured it'd be worth making them visible in some way while avoiding triggering an extra run of CI; I have tried out the new test case added for join_view locally.

[StephanTLavavej]

Thanks! I'll go ahead and push changes for these trivial code review comments.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for improving join_view on Clang - and congratulations on your first microsoft/STL pull request! 🎉 😸 🚀

This will ship in VS 2022 17.2 Preview 2.