<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=442002) </details> <!--IssueSummary end--> ### Background When base and HEAD diff of a MR has differences (e.g. base diff contains 2 files, HEAD diff contains 1 file), the count shown on the "Changes" tab when the MR page loads will be different once user views the "Changes" tab. Example MR: https://gitlab.com/patrickbajao/verification/-/merge_requests/88. ### Proposal Modify `Projects::MergeRequestsController#get_diffs_count` to get the `diff_size` of `MergeRequest#merge_head_diff`. We have to ensure we only do so if we're actually showing HEAD diff on the changes tab as well because it can show incorrect count for a moment if they're not consistent. We can use the same checks in [this code](https://gitlab.com/gitlab-org/gitlab/-/blob/222b78d3a2a5c3ba8cce745d63a6b1da86e91423/app/controllers/projects/merge_requests/diffs_controller.rb#L219-224) except for the `diff_head` param check as we don't pass that when we load the MR page.