format_on_save: save only changed lines

[HendrikJan]

Description

Currently format_on_save has two options: "on" and "off".

It would be useful to have the option "only changed lines", so that only lines that you just edited will be formatted.
This way your coworkers will not be confronted with all indentation changes in a pull request.

It would be nice if the same logic could also suppress jitter from remove_trailing_whitespace_on_save / ensure_final_newline_on_save changes.

[pjv]

This is really a nearly critical feature for making small fixes in someone else’s code and then submitting a PR. If your personal format settings don’t happen to match the whole file and you submit a PR that reformats 90% of a file because you modified one line that would be not ok. Having to be very careful and manual about this is an annoyance.

[NathBabs]

has this been added ? please

[rucoder]

Is there any plan to implement this?