(comment thread)

Code block Metadata block Note block MR block (we should still be able to interact with the MR as a whole thing, e.g. leaving a generic comment on the whole thing)

A user wants to comment on a single parameter name in a function. It is highlighted as a unique part of the syntax tree, and they're not happy with the particular name the author of the MR chose. Problem: The user can only comment on the entire line, because "lines" are considered the most fundamental building block in our Diffs UI.

A reviewer would like to open a discussion on the MR description because they disagree with some of the conclusions, but want more clarification. Problem: The only way to have a conversation about the MR metadata (like title, description, labels, etc.) is to open a generic note on the whole MR. There's no way to scope a discussion to a part of the MR.