Nullability friendly builder

Most of the static code analysis tools such as NullAway and infer throws error with the current builder setup.

There are 2 issues:

1. Builder fields are not annotated.
2. Builder fields can’t be non-null with the current setup since the constructor is usually empty.

public Builder() {}

public Builder nonNullField(@NonNull String nonNullField) {}

public Builder nullableField(@Nullable String nullableField) {}

An alternate way will be to set all the required values in Builder’s constructor and only have separate methods for Nullable fields.

public Builder(@NonNull String nonNullField) {}

public Builder nullableField(@Nullable String nullableField) {}

Since this breaks backward compatibility it needed to be flagged.

Complete class - https://gist.github.com/bangarharshit/c4ec0bee365cc4ef30270f10d4d1aa2f

[benjamin-bader]

Thanks for the demo project! I see that NullAway indeed doesn’t like the builder fields being without annotations.

I think it’s interesting that there’s no warning in the Arbit constructor - looks like the tool is smart enough to see that the ctor is manually checking for null and throwing? In that case, how about just annotating every builder field as @Nullable, and annotating the setter parameters according to the field’s requiredness? e.g.

class ArbitBuilder {
  @Nullable String requiredField = null;
  @Nullable String optionalField = null;

  ArbitBuilder setRequiredField(@NonNull String required) {
    ...
  }

  ArbitBuilder setOptionalField(@Nullable String optionalField) {
    ...
  }
}

This way, the tool would be satisfied, and the annotations themselves would still be honest. Does that sound like it would work? What do you think?

[benjamin-bader]

Fixed in #164.