Null safety strictness levels

[RealyUniqueName]

Something like

--macro nullSafety("pack", Weak)

For TypeScript-like null safety.

And

--macro nullSafety("pack", Strict)

For Kotlin level of strictness.

Rough example to showcase the difference:

function example(o:{field:Null<String>}) {
  if(o.field != null) {
    mutate(o);
    var notNullable:String = o.f;
  }
}

function mutate(o:{field:Null<String>}) {
  o.field = null;
}

The Weak null safety would not complain about such code, while the Strict one will emit an error on var notNullable:String = o.f; because o.f could be changed to null in mutate(o) call.

If different modes are used in the same build, a warning should be emitted and the least strict mode used.

[Gama11]

What about @:nullSafety meta? Would @:nullSafety(false) become @:nullSafety(Off) so you can have @:nullSafety(Weak) and @:nullSafety(Strict)?

[RealyUniqueName]

I don't want to support mixed modes )

[Gama11]

The ability to set it per package doesn't count as "mixed modes"?

[Simn]

I don't want to support mixed modes )

Any technical reason for that? If we configure this per-field anyway I don't see much of a problem with it.

We could have this:

@:nullSafety(false) // no null-safety checks
@:nullSafety == @:nullSafety(true) == @:nullSafety(Weak) // TypeScript
@:nullSafety(Strict) // Kotlin

[RealyUniqueName]

I'm scared that in the end I'll have to support different modes for different expressions in the single method body :)

[Gama11]

@Simn Hm, supporting both Bool and a strictness "enum" seems unnecessary / confusing.. If there's ever typed meta that would turn into something like EitherType<Bool, NullSafetyStrictness>?

("null safety off" also sounds a bit better in my head than "null safety false")

[RealyUniqueName]

That can be like Strict, Weak, Off

[RealyUniqueName]

But then again, if it's supported per package/field, then why not per expression? )

[Simn]

I guess we don't need the bools. I treated it like it's the existing way to configure, but I suppose we are still free to change it.