Should all server capabilities allow the corresponding dynamic registration options?

Some, but not all, of the server capability fields in the initialize response allow providing the corresponding registration options. It's helpful to be able to do so, since the registration options type usually includes additional fields, such as the documentSelector.

Examples:

• completionProvider has type CompletionOptions and doesn't allow CompletionRegistrationOptions
• typeDefinitionProvider has type TypeDefinitionOptions | TypeDefinitionRegistrationOptions

Is this just for backwards compatibility? Is there a way we could migrate the protocol to be more consistent here? It would make things simpler. For example, if you want to make use of the documentSelector capability, you can have many cases:

• Client supports dynamic registration: dynamically register
• Client does not support dynamic registration:
  • Options field supports dynamic registration options: statically register
  • Options field does not support dynamic registration options: give up

It's quite fiddly.

Start by comparing the server capability types in the initialize response, especially completionProvider and typeDefinitionProvider, with their corresponding registration option types. Determine the backwards-compatibility constraints and whether a consistent migration is possible; done means the protocol has a decided, documented approach rather than an unresolved set of cases.