OTOH, as part of a bug report, I can just point Microsoft to the Boost PP tests which are failing or producing incorrect warnings, but I doubt that is acceptable as a bug report on which they will act.
Outcome has been part of MSVC's test suite for some months now, as is Boost. Outcome has broken MSVC in all sorts of subtle and interesting corner case ways. Microsoft have spotted the failure within 24 hours, triaged it, and self fixed the problem, usually providing an ETA of when the compiler fix will ship. So Edward if I were you, I'd make Boost.Preprocessor and Boost.VMD for the 1.69 release use standard preprocessor if you detect it is enabled in MSVC. That'll cause MSVC to fail in the Boost conformance testing. That in turn will ensure Microsoft triage and fix all outstanding problems in super quick time. That's my recommendation to you, anyway. Niall