Looking here https://gitlab.haskell.org/ghc/ghc/merge_requests/116//diffs I see literally NO discussions with a "toggle discussion" button. Indeed if I search for "toggle" I get no hits.
Oh, I see, you are right with respect to the link you cited now. None of the buttons help, just as you say. I have to navigate back from the "Changes" to the "Discussion" tab, which gets me to the link you gave initially (https://gitlab.haskell.org/ghc/ghc/merge_requests/116) where the discussions are available, but I can't see them in the context of the whole diff and none of the buttons there let me extend the view of the diff. That's quite suboptimal. Could you confirm that at https://gitlab.haskell.org/ghc/ghc/merge_requests/116 (without the 'diff' at the end) you can see the collapsed discussion items?