Add ocaml-language-server for OCaml and ReasonML

[jungomi]

ocaml-language-server provides editor support for OCaml and Reason using the Language Server Protocol.

I had to remove the id field on the request object, because technically a notification must not have an id, which is different from id: null (present, but null).

From JSON-RPC 2.0 Specification - Notification

4.1 Notification
A Notification is a Request object without an "id" member. [...]

And JSON-RPC 2.0 Specification - Request object:

id
An identifier established by the Client that MUST contain a String, Number, or NULL value if included. If it is not included it is assumed to be a notification. The value SHOULD normally not be Null [1] and Numbers SHOULD NOT contain fractional parts [2]

[...]

[1] The use of Null as a value for the id member in a Request object is discouraged, because this specification uses a value of Null for Responses with an unknown id. Also, because JSON-RPC 1.0 uses an id value of Null for Notifications this could cause confusion in handling.

ocaml-language-server is built with vscode-languageserver, which is very strict about this and does not accept notifications with an id, even if it's null.

After removing 'id': v:null, Vim reorders the fields to {"method": "someMethod", "jsonrpc": "2.0"} for whatever reason, so I swapped them in the source to avoid confusion. The order only affects the tests.

For the record:

echo {'id': v:null, 'jsonrpc': '2.0', 'method': 'someMethod'}
" => {'id': v:null, 'jsonrpc': '2.0', 'method': 'someMethod'}

echo {'jsonrpc': '2.0', 'method': 'someMethod'}
" => {'method': 'someMethod', 'jsonrpc': '2.0'}

echo {'jsonrpc': '2.0', 'method': 'someMethod', 'id': v:null}
" => {'method': 'someMethod', 'jsonrpc': '2.0', 'id': v:null}

[w0rp]

Looks good. I'll merge this for the JSONRPC changes.

Could you create a follow up pull request with tests for the new linter functions? That's the best way to protect against regressions.

[w0rp]

Cheers! 🍻