Allow extending HAL-Forms media type

[reda-alaoui]

Today, many HAL-FORMS components such as HalFormsMediaTypeConfiguration and Jackson2HalFormsModule mixins are package private, while their HAL counterparts are public.

This prevents us from extending HAL-FORMS as allowed by the specification:

7. Extending the HAL-FORMS Document
Authors can extend the HAL-FORMS media type as long as the following rules are observed:

No existing properties or objects are removed.

No existing properties or objects or the list of valid values are altered in a way that is non-backward compatible (e.g. changes MUST NOT break existing implementations that adhere to this specification).

All new properties or objects are treated as OPTIONAL (e.g. no new REQUIRED elements are introduced in an extension).

Warning
Authors should be aware that a future version of this specification MAY add new elements and should take care that any extensions are implemented in a way that reduces the likelihood that a future version of this specification is in conflict with your extension.

Are there reasons to keep hiding these elements? Or could we consider make some public?

We'd like the following to become public:

• all inner classes of Jackson2HalFormsModule
• HalFormsMediaTypeConfiguration

[odrotbohm]

Are there reasons to keep hiding these elements?

As always, the primary reason for that is that, right now, we can change them at will without the risk of breaking any code that would refer to it because, by definition, it can't.

Or could we consider make some public?

Yes, but I'd consider that a last resort after discussing particular extension scenarios that shape which parts we really need to open up.

Some of the public HAL components are likely public by oversight. Skimming through the codebase, I am not convinced that trying to customize a standard media by solely extending or declaring configuration extending existing classes will work as expected. Primarily due to the way we currently find and register configuration for these default media types. Happy to revisit that, too, but—as indicated above—we should discuss what you'd like to achieve in the first place.

[reda-alaoui]

Hello @odrotbohm ,

The use case that lead to the creation of this issue is as follow: we'd like to add arbitrary attributes to the property element.

[odrotbohm]

I.e., what you reported in GH-2345? If so, let's continue there and see how much more general stuff is required to tackle here then.

[reda-alaoui]

Ok 👍