Generate primitive types for non-null GraphQL types

[joffrey-bion]

Is your feature request related to a problem? Please describe.
Using wrapper classes for primitive types incurs a performance cost.
Wrappers are useful to indicate when a value can be null, but if it is declared as non-null (!), we have no reason to use the wrapper type (it's even confusing for readers).

Describe the solution you'd like
Non-null primitive GraphQL types should be mapped to non-wrapped primitive Java types.

Note: For backwards compatibility, we could add a config flag to generate boxed types all the time, but I believe Java's autoboxing/unboxing should actually make this change backwards compatible without the need for a config flag.

Describe alternatives you've considered
Currently, there is no way to customize the generation, AFAICT.
The customTypesMapping argument cannot be used with a ! (at least in Maven).

Additional context
Add any other context or screenshots about the feature request here.

[kobylynskyi]

@joffrey-bion good idea.
Just to confirm, we are talking about:

• GraphQL Int
  • Non-null -> Java int
  • Nullable -> Java Integer
• GraphQL Float
  • Non-null -> Java double
  • Nullable -> Java Double
• GraphQL Boolean
  • Non-null -> Java boolean
  • Nullable -> Java Boolean

[joffrey-bion]

@kobylynskyi yes exactly 👍

[kobylynskyi]

@joffrey-bion actually I just found out that it is a breaking change.
Suppose you have a graphql schema

type Query {
    feeds(amount: Int!): [Feed!]
}

and corresponding resolver:

public class FeedsQueryResolverImpl implements FeedsQueryResolver {
    @Override
    public List<Feed> feeds(Integer amount) { return null; }
}

Now (after my recent changes) FeedsQueryResolver will be generated with primitive parameter:

public interface FeedsQueryResolver {
    List<Feed> feeds(int amount);
}

and FeedsQueryResolverImpl will not compile anymore.

So I might bump the next release version to 4.0.0 (instead of 3.2.0)

[joffrey-bion]

Makes sense, it is indeed a breaking change