[bv-dev] Container element validation for arrays

[Gunnar Morling]

Hi,

Guillaume made an important observation concerning the validation of
array elements. So far we envisioned to support this:

    String @Email [] emails;

That looks nice (provided that @Email supports TYPE_USE), only that
it's getting semantics of type annotations for arrays wrong.

As per the JLS [1], the @Email annotation here applies to the array
type String[], not the component type String. This example from the
JLS clarifies the intent:

    @C int @A [] @B [] f;

    "@A applies to the array type int[][], @B applies to its component
type int[],
    and @C applies to the element type int."

So according to that, our example would have to be:

    @Email String[] emails;

But obviously this conflicts with the existing semantics of applying
constraints to arrays (not their elements) in BV 1.1.

So based on that, I don't see a good way for supporting container
element constraints for arrays. Hence my suggestion is to not support
them in the BV 2.0 spec (the validation of container elements of
generic containers - List<@Email String> - is not affected). Specific
implementations may explore ways around it (e.g. specifying the target
via payload()) and we may revisit it in 2.1.

Any thoughts?

--Gunnar

[1] https://docs.oracle.com/javase/specs/jls/se8/html/jls-9.html#jls-9.7.4