Consider changes to MergedAnnotation.asMap

[philwebb]

It's currently quite hard to convert a MergedAnnotation to an AnnotationAttributes instance. At one point early in the design we had a factory method on AnnotationAttributes that allowed it to be used with asMap:

mergedAnnotation.asMap(AnnotationAttributes::ifPresent);

We removed that because it wasn't great having an asMap method that could return null.

Originally I didn't want to tie MergedAnnotation to AnnotationAttributes because I thought there was too much overlap. In hindsight, I'm not sure we can ever remove AnnotationAttributes so perhaps we should just embrace it and add an asAnnotationAttributes method. We could even drop asMap and the custom factory version which probably only exists to support AnnotationAttributes.

We should also reconsider the MapValues enum name. It's not that great.

[jhoeller]

Let's try to sort this out for 5.2 M1 still since we got time until Tuesday now.

[philwebb]

Replacing the asMap method might be a little more tricky that I first thought. We use the factory method ourselves to create AnnotationAttributes with different constructors. I think we'll need a bit more feedback from @odrotbohm to see how he's making use of those methods.

[philwebb]

I added an extra asAnnotationAttributes method and also renamed MapValue. Feel free re-open or comment if anything else can be improved.