Until we are on C+20, we should pass /Zc:lambda to msvc. It is implied by /std:c+20 and higher, but must be passed explicitly before then. It will tell msvc to use a standards-conforming lambda parser rather than whatever it is they were doing before. This was recomended by the MSVC team in response to a bug I filed about hitting an ICE.

It is probably worth doing this on any branch with a new enough MSVC that we still backport to in order to minimize surprising compiler errors when backporting. On older version of MSVC 2019 it was spelled /experimental:newLambdaProcessor, but the documentation seems to imply that it is just a different spelling of the same flag.