client->server request: Join Lines

Meta: I am in the process of formalizing protocol extensions, used by rust-analyzer. I will be filing issues for generally useful extensions. Here's the doc where we will document our extensions.

joinLines

Server Capability: { "joinLines": boolean }

This request is send from client to server to handle "Join Lines" editor action.

Method: experimental/JoinLines

Request:

interface JoinLinesParams {
    textDocument: TextDocumentIdentifier,
    /// Currently active selections/cursor offsets.
    /// This is an array to support multiple cursors.
    ranges: Range[],
}

Response:

TextEdit[]

Example

fn main() {
    /*cursor here*/let x = {
        92
    };
}

experimental/joinLines yields (curly braces are automagiacally removed)

fn main() {
    let x = 92;
}

Unresolved Question

• What is the position of the cursor after joinLines?
  Currently this is left to editor's discretion, but it might be useful to specify on the server via snippets.
  However, it then becomes unclear how it works with multi cursor.

Start with the joinLines specification in this issue and the linked rust-analyzer docs/dev/lsp-extensions.md. Review the request parameters, response type, example transformation, and unresolved cursor-position question. Done means the extension's behavior and cursor semantics are agreed and documented clearly enough for clients and servers to implement.