Implement non-null assertions

[dcodeIO]

Similar to #235, but implemented as another kind of assertion.

[MaxGraey]

Is it valid?
return foo.bar!!;
arr!!![0]

NOTE
Ok, see it valid. great!

[MaxGraey]

LGTM

[MaxGraey]

How about that?:

export function testFn3(fn?: (() => Foo | null)): Foo | null {
  return fn!();
}

[dcodeIO]

That fails to compile because we don't support fn?:. The following with an initializer as we require it errors for other reasons, though:

export function testFn3(fn: (() => Foo | null) | null = null): Foo | null {
  return fn!();
}

ERROR AS200: Conversion from type 'usize' to '(() => Foo | null) | null' requires an explicit cast.

Something off with assigning null to a nullable function type as it seems, but probably an issue on its own.

[MaxGraey]

Yeah. This relate to how handle of undefined type. Because arg?: Foo produce arg: Foo | undefined. So this make sense for different PR. But first need decide if we need support this semantics and may be force it to null? Like arg?: Fooshould be same as arg: Foo | null = null

[dcodeIO]

Leads us to nullable basic types as well then, like a?: i32. Might be too early to decide.

[MaxGraey]

Same as a: i32 | null. Currently this valid but not handle properly. I suggest use a?: Ref as short alias for a: Ref | null = null and a?: i32 as a: i32 = 0. WDYT?

[MaxGraey]

Also found problem with Foo | null | null which valid on TS but currently fail in AS

[dcodeIO]

Yeah, i32 | null should emit at least a warning. Can take a look at that later.

[MaxGraey]

But may be Foo | null | null issue better fix in separate PR.