commit f99db3e3540f06c7e7eaf40f984543131b8c021a
author Devin Jeanpierre <jeanpierreda@google.com> Wed Apr 27 23:10:33 2022 -0700
committer Copybara-Service <copybara-worker@google.com> Wed Apr 27 23:10:58 2022 -0700
tree 01575328a2d6d4a8bc15623fc2a91de34d2ecb09
parent b4ae6383061ed665c4841d06eec87b52ca62032c

Implement upcast to virtual base, via synthesized C++ thunk.

This (or rather, the preceding work from earlier CLs) is probably the rest of the questionable part for implementing casting in C++. We need some infrastructure somewhere to support dynamic casts -- not just casting to virtual base (which isn't super interesting right now), but even `dynamic_cast` in its full generality.

Remaining work:

* Fix the hacks in the implementation: this doesn't support cross-crate inheritance, name collisions, etc. -- it's a very rough first pass still.
* Flesh out the matrix of conversions. Right now, this still only does &T->&U, but of course we also need to support this for (pinned) mutable references, and raw pointers.
* Flesh out the casting directions: in particular, we also need to support downcasting.

So, you know, first 90% down, only 90% left. :)

PiperOrigin-RevId: 445065670