I use the "undo" functionality in my editor. In emacs it's a complete tree of changes so you can't really lose anything.

It's something but it's ephemeral and not shareable. You can't reconstruct how a piece of code got written weeks later, to eg recover some debug helpers you deleted without committing because you thought you were done with debugging it.

But thanks for the tip about Emacs undo tree, didn't know about that. With some add-ons you can apparently eg find undoable changes for only some region of a buffer, etc.

> With some add-ons you can apparently eg find undoable changes for only some region of a buffer, etc.

This is built into Emacs (no add-ons needed). Calling undo with a region selected undoes changes only in that region.

You can also setup undo-tree to show a diff for every change.

True, but that's no guarantee you'll ever be able to actually find it.

That could be interesting but the right structure (off the top of my head) would be a hierarchical layer - not this flat monstrosity!

I actually disagree with this because I think you should try to have the project even vaguely work at each commit, so "git bisect" will work. But maybe each commit could be a log of keystrokes instead of a text diff.