implement json_object with separate keys and values arguments

[valkrypton]

added support for json_object(keys[],values[]) under #4216

[guissalustiano]

Thanks for open the PR!
The changes look good to me.

[valkrypton]

@weiznich i came up with this type signature

fn json_object_with_keys_and_values<K: TextArrayOrNullableTextArray + MaybeNullableValue<Json>, V: TextArrayOrNullableTextArray + MaybeNullableValue<Json>>(
        keys: K, values: V
    ) -> K::Out;

to fix the auto_type error but i dont know if it's correct or not?

[weiznich]

Unfortunately that's still not 100% correct as it only couples the nullability of the return value onto the first argument, but this function seems to return also Null if you pass in Null as second argument. (I'm sorry that null value handling is such a mess. I also feel that postgres doesn't document this in a good fashion at all.)

I cannot say without further experimentation how to solve this. I will update the comment as soon as I know more.

[valkrypton]

I did write a doc test where the 2nd argument is null and it returns null as expected, but you're right that the output is coupled with the first argument only. I couldn't think of a way to couple it with both arguments

[valkrypton]

@weiznich i made a small change to the signature, take a look now

[weiznich]

I've pushed b488df4 which introduces a new helper trait that essentially evaluates to Nullable<Out> if one of the input types in nullable, that should fix the issue.