ListDataDefinition::toArray is missing the data type

Triaged as part of BSI.

Is this still an issue? Also, since my knowledge of this system is severely lacking, does this lead to other bugs? Might be good to get a use case of what this issue leads to.

I'd agree that this is unexpected behavior, thus qualifying it as bug seems ok. let's improve this.

@fago are you able to answer any of the questions in #5?

let me try:
well, without the type you cannot re-create the data definition based upon the toArray()
This works well when working with other classes based upon DataDefinition, but apparently not for lists.

I don't see it causing subtle other bugs, still it's not working as it should, thus qualifying it as bug seems right to me.

I made the indicated changes. I can change the visibility of THIS_TYPE or 'self' to 'static' if necessary. What would be a good way to test this out?

This steps to reproduce are screaming to be converted into a test.

Created a test only MR. I decided the best approach to expose this bug was to add similar extensions of test coverage to the other TypedDataDefinition tests.

I've added the test to the main MR and I expect that the test will fail in the test-only MR but that the same test will pass in the main MR.

The constant isn't necessary but it might be a good idea to make clear that it won't change and that the uses of 'list' are the same semantically.

Seems have two open threads.

For the constant would say not sure it's needed either. Looking at how SequenceDataDefinition is done they don't use a constant.

I can just hardcode 'list' if necessary, but, IMHO, there's already too much use of hardcoded strings in Drupal.