I have seen a few Pull/Merge Requests come through recently where the author decided to apply their bugfix/logic/feature changes, but in the course of doing that they’ve also made a couple of changes to the legacy code as well which uses tabs for indentation. So in doing that they decided to apply the new style rules for new code (4 space indentation) to the whole bunch of legacy files they changed. For the code reviewer this involves reading pages and pages of code to find the real changes. Sometimes git/GitHub even gets confused and the changes are appearing to be completely different in the side-by-side view.
What is best practice here?
Should the legacy be code be kept as-is style/indentation wise?
Or should a different PR with only styling changes be applied to all that legacy code to bring it up to date with the new style rules? Unfortunately any PRs being worked on will get major conflicts.