Only the special nullability attributes (`_Nonnull`) work correctly
through type aliases like we're using with `Ptr`. But they aren't
strictly UB and so have to be specially enabled in our sanitizer config
in order to usefully catch nullness errors early. Turn on those
sanitizers as well.
Also, now that we are using fully remote build output caching for our
CI and not trying to squeeze under an arbitrary size limit, re-enable
the nice error messages for all the UBSan checks.
Note that this will have a (very) slow CI run as it will have to
recompile ~everything and upload fresh artifacts. But those should then
be effective cache hits going forward.
The advantage is a C++ pointer is special, and this approach eliminates the Ptr class type that was causing problems in conversions. Attribute suggestion was courtesy of chandlerc. We're sticking with the Ptr name because it's shorter than Nonnull, and we're likely to keep this in lots of places.
With this, only main.cpp instantiates an arena. Maybe we'll want to split that up more later (e.g., so that the runtime interpreter uses its own arena), but given the intent to have type-checking update the AST, I thought this was a reasonable approach for now in order to avoid ownership complexities.
Fixes#769
Chandler Carruth
Jon Meow
Geoff Romer