Fred Emmott

This was previously reported internally (FB T47005436) as a typechecker bug, but personally, I agree, this seems like behavior the runtime should permit and the typechecker is correct. This is...

Very similar to your repro: https://gist.github.com/fredemmott/8a0fbc05511f6ddc77b9c4f2ec3cdf0a Contains both an interfaces version, and an 'abstract protected' version that IMO should behave equivalently, but doesn't

We have an internal extension - I'm unsure if it would be suitable for wider release - @terrelln ?

recentish feedback on union types from @dlreeves * What if someone makes a union of 100, 1000 or even 10000 types? How can we prevent this since it would absolutely...

Yes; unions are pretty unlikely to be supported, but intersection types are more promising. This is mostly due to the likelyhood of widespread use of union types leading to performance...

> has any other language suffered from this? This is a significant problem for Flow, which shares a lot with Hack, and is a smaller amount of code (at FB)...

> this changed to a fatal error This was a 'fatal error', however we previously threw even for 'non-recoverable' fatal errors. This one probably shouldn't have been a fatal error...

@vsiles @CatherineGasnier https://github.com/facebook/hhvm/commit/53a12e25ee56d140ddf57a9dc475f834f1d8f890 from @sarahhenkens is a suggested fix for this which appears to work, but looks like it's essentially a revert 7824d828cff1c9fcf2f9c2fc6f320a7d99afd73b - do you have context to share...

Notably the array_fill dict path does have `CheckAllocation {}` passed to the DArrayInit

FB T97062050