Kotlin nullability feature for typesafe client (client model)

[mskacelik]

/cc @jmartisk
Ok, so with nullabilities in Kotlin, it is a bit complicated; when not having an ? nullable operator for types, Kotlin automatically adds its own Kotlin @NonNull annotations, but not ALWAYS. For example, when having a List<String>, the annotation is only applied on the List<> part but not the argument String. So, making these two codes indistinguishable (via Jandex):

List<String?> // List<String>

On top of that, there are some weird behaviors like annotation is applied only on MethodParameterInfo and not the Type

So, I only added a simple Kotlin nullability feature (see tests). So it can be consistent with the server side.
Java reflection implementation of typesafe client still does not have Kotlin nullability checking (todo?).

issue: #2142
@robp94

[jmartisk]

@robp94 would you be willing to give this a try and see if it suits your expectations?

[robp94]

Looks good to me.

[mskacelik]

I played a bit with the MP @NonNull annotations now (with -Xemit-jvm-type-annotations flag) and it seems to work with Kotlin now if we explicitly annotate inside of wrappers.

@Mutation
    fun testMatrix(working: List<@NonNull String>): Boolean {
        println("hello world")
        return true
    }

schema:

"Mutation root"
type Mutation {
  testMatrix(working: [String!]!): Boolean!
}

edit: I know it worked before the PR, but it could be substitute of an explicit nullability of Kotlin (inside generic arguments). Gonna try add some server-side tests.

[jmartisk]

@mskacelik please add a little note (about having to add this flag) to our documentation, it will be useful to many developers

[mskacelik]

Ok, it seems to have some problems regarding nested Lists, i.e.: List<List<Int>> only generates [Int] (only in Kotlin, Java works (server side)).

But I think I found a bigger problem, in Quarkus @NonNull annotations seem to be very inconsistent after HOT RELOAD.
For example:

>quarkus dev
List<@NonNull String> => generates [String!]!
changes code to Array<@NonNull String> => generates [String]! (HOT RELOAD)
...terminates app...
>quarkus dev
Array<@NonNull String> => generates [String!]! 
changes code to List<@NonNull String> => generates [String]! (HOT RELOAD)

Very strange (once again AFAIK only Kotlin is doing this)