bug#37774: 27.0.50; new :extend attribute broke visuals of all themes and other packages

[Andrey Orst]

Git diff is an inline diff. It doesn't need changes to be aligned side by side,
and doesn't need changes to be linked as in side by side diff tools like,
meld, and diff-viewers in Intellij Idea[1], VSCode[2], Sublime Merge[3], Smartgit[4],

[1] https://www.oreilly.com/library/view/intellij-idea-essentials/9781784396930/graphics/6930OT_03_44.jpg
[2] https://www.meziantou.net/assets/result1.png?v=2c344912
[3] https://edge.alluremedia.com.au/m/l/2018/09/smerge.png
[4] https://www.syntevo.com/assets/images/products/smartgit/opener-481720cb.png

and even when we looking at inline diff,

most GUI tools use extended highlighters,

because it is easy to understand:

sublime merge: https://i.ytimg.com/vi/ZrdkEBJV660/maxresdefault.jpg

Magit: https://magit.vc/screenshots/commit-top.png

Consider looking at how magit supposed to look in official screenshots here,

and how it looks after the change. https://emacsair.me/2017/09/01/magit-walk-through/
--
Best regards,
Andrey Orst