[NNBD] Provide a way to check if a type is nullable

[pedromassango]

I'm not sure if this currently exist but I didn't found anything by looking at the docs. Also not sure if here is the right place for this proposal!

In Kotlin we are able to check whether a type is nullable or not.
Wondering if currently there is a way of doing that and if not we can consider this as a proposal.

In Kotlin we can achieve this by using reflections:
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect/-k-type/is-marked-nullable.html

We can have TypeMirror.isNullable or isMarkedNullable which is true if the type was declared with a question mark (nullable) or false otherwise.

[leafpetersen]

If I understand correctly, you're asking about reflective support in dart:mirrors for nullable types? Note that for non-reflective uses null is T works for this.

[pedromassango]

null is T

@leafpetersen what if I want to check an actual property?

String? foo;

// somewhere in my code


if (foo.isNullable) {
  ...
}

I actually need this to build a linter related to nullable return types. See dart-lang/linter#2352.

Cc @kevmoo

[leafpetersen]

Lints are generally written using the analyzer APIs, which is more like a compiler model than a code generation model. I'm not sure what you're looking for here, but I don't think this is a language feature request. Perhaps follow up in the lint issue?