xo-umbrella2/xo-reflectable2

xo-reflectable2

The AReflectable facet -- reflection for facet-object-model (fomo) data types, so c++ code can interrogate a fomo object at runtime without knowing its representation. First consumer is xo-printjson.

Scaffold. idl/Reflectable.json5 declares no methods, so AReflectable is empty and nothing implements it yet. The method it will carry is self_tp(), returning a xo::reflect::TaggedPtr for the object's concrete representation -- the fomo counterpart to xo::reflect::SelfTagging::self_tp(). Design and remaining tickets: .xo-backlog/reflectable2/.

xo-reflect is deliberately NOT modified by any of this. TypeDescrExtra and EstablishTdx are public extension points, so the fomo-aware pieces can be supplied from here instead. That matters because reflect has far more dependents than facet does, and hosting them in reflect would hand every one of them a dependency on xo-facet:

for s in $(xo-deps --users-of=xo-reflect --format=names -q); do
    xo-deps --why=$s:xo-facet -q >/dev/null || echo "$s"
done

It is scaffolded rather than left as a bare directory so that xo-build --all covers every entry in xo-cmake/etc/xo/subsystem-list; a subsystem listed there but carrying no CMakeLists.txt makes --all fail at the configure step.

Namespace is xo::reflect -- shared with xo-reflect rather than separate, since the facet is part of reflection and its method sits beside SelfTagging's. xo-ppsink and xo-indentlog2 share xo::pp the same way.

To add the method: edit idl/Reflectable.json5, then rebuild -- xo_add_genfacet regenerates include/xo/reflectable2/detail/ and src/reflectable2/IReflectable_Any.cpp, both of which are checked in.