MR Review: create a new comment on the diff

Problem to solve

The extension only allows creating new comments on the "Details" webview which means they are not related to any particular position. To replicate the GitLab web experience, this ~feature implements creating new comments in the MR diff view.

Proposal

new_comments

Implement a command that will be triggered when the user clicks "Add comment now" button:

This command will create a new comment. It will support unchanged, removed, and added lines.

Further details

Creating comments

GraphQL mutation

mutation CreateDiffNote5 {
  createDiffNote(
    input: {
      noteableId: "gid://gitlab/MergeRequest/87196674"
      body: "new note"
      position: {
        baseSha: "5e6dffa282c5129aa67cd227a0429be21bfdaf80"
        headSha: "a2616e0fea06c8b5188e4064a76d623afbf97b0c"
        startSha: "5e6dffa282c5129aa67cd227a0429be21bfdaf80"
        paths: { oldPath: "/test.js", newPath: "/test.ts" }
        newLine: 15
      }
    }
  ) {
    errors
  }
}

All attributes are mandatory, except for the following exception regarding newLine and oldLine:

type of line we comment on	newLine, oldLine explained
added line (right-hand-side of the diff)	We only submit `newLine`
removed line (left-hand-side of the diff)	We only submit `oldLine`
unchanged line	Both `newLine` and `oldLine` are required. If the unchanged line has a different index on each side of the diff, these attributes need to reflect that different index.

Representing the new comment in VS Code

The createDiffNote mutation gives us only the new note as a response. But we need the full discussion response because only the discussion contains replyId attribute that allows us to submit replies.

In other words, without knowing the replyId, we can create a new thread, but the user can't reply to that thread.

The only way how we can get it now is to ask for all discussions on MR and filter out the one that contains our new note.