Shift left or right (with `noet`) without converting existing spaces to tabs

Question

Foreword

I'm using the "indent with tabs, align with spaces" ideology for indentation. This means that each line in a file can be prefixed with an arbitrary amount of tabs and spaces (as opposed to "only spaces" or "tabs when possible, then 0 ≤ x < tabstop spaces"). For example:

<--># use OLS (ordinary least squares) to find initial guesses
<-->if prefit or initial is None:
<--><-->beta, cov = sp_opt.curve_fit(model,
<--><-->.............................xdata = x,
<--><-->.............................ydata = y,
<--><-->.............................sigma = yerr,
<--><-->.............................absolute_sigma = True,
<--><-->.............................maxfev = int(1e6),
<--><-->.............................p0 = initial)

Here, a <--> represents a tab character and . represents a whitespace.

To work in this mode, I have noexpandtab set in my vimrc. Hence this question on Vim SE is not relevant for me.

Question

When I shift such a line left or right using << or >> Vim operations, Vim replaces (almost) all existing spaces with tabs. How to avoid this?

I want Vim to only do exactly what's said — i. e. insert or remove a single tab character at position 0 of the line.

Answer 1

With the help of this, this, and this, I come up with this:

nnoremap >> 0i<tab><esc>^
nnoremap << :norm 0ldF<tab><enter>^

For multiline selection (works on VISUAL, VISUAL BLOCK and VISUAL LINE):

vnoremap > :norm 0i<tab><enter>gv
vnoremap < :norm 0ldF<tab><enter>gv

Put them on your ~/.vimrc.

Answer 2

:nnoremap >> I<tab><esc>^

:nnoremap << :s/\v^\t//<cr>

The first one will insert a tab at the start of the current line, without breaking any other characters.

The second one deletes the first character on the line only if it's a tab (by searching and replacing it with nothing). If you have hlsearch on, you can add a :noh call to the end of the second one to get rid of the highlighted residue.

Answer 3

Two things. If you really want to mix tabs and spaces, you really need to count on all spaces that are a complete tab stop, to be replaced with a tab. If you are having problems with using such a file for printing, or viewing on a web page or some other place where tab expansion there, is different than what you are using for editing, then filter your file through 'pr -te ' and that will remove all tabs and replace them with spaces.

I use 'pr -te 8' on files with odd tab practices and then do ":set ts=8 sw=8', '1G' '>G', '<G' and then ':set ts=4 sw=4' to use the tab expansions I use. There are all kinds of complaints about tabs vs spaces which have been on going for decades. In the end, the use of leading tabs produces a lot less hassle for formatting than 'spaces' does, and I can edit a lot faster in VI if I can use 'space' and 'backspace' to move past indentation levels than have to use 'l' and 'h' which require a hand position switch and typically a glance at the keyboard.

When you are just typing a new program, IDEs and other places where auto indent is done for you, you can feel comfortable and just ignore leading spaces. But in the end, it just creates problems when another person can't change indentation levels for themselves, to make the code more readable.