Collapsing diff in large MR takes a lot of time
### Summary Collapsing a file in a merge request takes several seconds (~15 seconds) and pegs one CPU the whole time. ### Steps to reproduce 1. Open https://gitlab.com/leipert/test-project/merge_requests/2 2. Go to the diff tab. Wait until page is loaded completely 3. Collapse the first file ### What is the current *bug* behavior? It takes several seconds to collapse the file ### What is the expected *correct* behavior? It should collapse the file instantly. ### Relevant logs and/or screenshots ![several-second-diff](/uploads/d90157477ecff6b5db7e2cb348148aee/several-second-diff.webm) - Start of collapse: 2.8s - End of collapse: 17.97s
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