going back multiple undo steps with undo-in-region

Question

I'm trying to use undo in a region to undo multiple changes -- but I can only toggle between undoing one change and redoing it.

For example, if I start with:

Here is line 1 with some text.

Line 2 is here.

Line 3 is, naturally enough, after line 2.

I make a change first to line 1, then to line 3:

Here is line 1 with some FIRST-CHANGE text.

Line 2 is here.

Line 3 is, naturally enough, after line 2. SECOND-CHANGE

Then I go back and change line 1 again:

Here is line 1 with some FIRST-CHANGE text. And THIRD CHANGE too!

Line 2 is here.

Line 3 is, naturally enough, after line 2. SECOND-CHANGE

I want to undo all the changes to line 1 but leave the others. So I select a region with just line 1 and do C-/ to undo in region. That just removes the final exclamation point:

Here is line 1 with some FIRST-CHANGE text. And THIRD CHANGE too

Line 2 is here.

Line 3 is, naturally enough, after line 2. SECOND-CHANGE

Okay, I want to keep going. I select line 1 again, do C-/ again, and get the exclamation point back!

If I use regular undo, I can just keep undoing through previous changes.

Is there a way to do the same with a region?

I've tried undo-redo but that doesn't do what I want.

Is there a way to undo everything in line 1 but keep line 3 as it is?

Answer 1

The cause of the problem is:

I select line 1 again

You don't need to re-select the region every time (which would be a very cumbersome requirement) -- Emacs knows to continue undoing in that region. Just select the region once and then type C-/ as many times as necessary.

The act of selecting a region breaks the undo chain (it's not an undo command), and so the subsequent undo is starting a new chain by undoing the most recent change (which was an undo -- hence the "redo"). (You maybe then repeated that cycle creating even more copies of the undo/redo sequence to move through.)

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Note that you can also use M-x undo-only to undo without undoing undo commands in the list. If you then repeat that (C-xzzzz...) you'll get back to where you want to be quickly, even if you'd accidentally introduced some "redos" into the undo list along the way.

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I've tried undo-redo but that doesn't do what I want.

For clarity, that command performs a "redo" (which was what you were trying to avoid doing).