Add :retab command

[FrostyX]

See "Changing tabs" section in the Vim manual
https://vimhelp.org/change.txt.html#change.txt

[tomdl89]

Thanks fort the PR @FrostyX . Please add some tests so a) I can easily see what your implementation does and b) to guard against regressions in the future. Cheers

[FrostyX]

Thank you very much for the review @tomdl89,
I was a bit worried that it will be complicated to write the tests but I was sooo wrong. The tests are so comfortable to write thanks to the evil-test-buffer.

Updated, PTAL :-)

[tomdl89]

Looks great - thanks for the tests @FrostyX ! Just need to get that Retab only selected lines test passing and I'm happy to merge :)

[FrostyX]

Yeah, I am trying to figure out what is wrong. As these things usually go, the test works fine on my machine.

[tomdl89]

FWIW, they pass on my machine too with make emacs and make terminal but not with make test (which is what github actions uses), so the --batch option may be causing some differences.

[tomdl89]

OK, having looked at this, and got it passing for each, but never together, I'd be happy to remove this test. It shows a difference between --batch mode and normal mode which I don't understand. A minimal repro (without evil) for the emacs dev mailing list may be interesting if you can't work out what causes the difference. Up to you.

[FrostyX]

Thank you very much for trying to debug the issue.

I'd be happy to remove this test.

Do you mind if we skip the tests in the batch mode instead? I updated the PR. I think it is worth showing what the command is supposed to do, as you said in

a) I can easily see what your implementation does

[tomdl89]

Yup, all good. Thanks again for the PR!

[FrostyX]

Thank you very much.