Make Vim _really_ work with both spaces and tabs

Question

Here is what I use for indentation:

set autoindent
set breakindent
set expandtab
set smarttab
set shiftround
set shiftwidth=2 softtabstop=-1  " or maybe shiftwidth=2 softtabstop=8

" https://vi.stackexchange.com/a/15557
inoremap <tab> <c-v><tab>

When I press >>, this indents my code 2 spaces; and when I press Tab, this inserts the tab character. Fine, isn't it?

However, there is a problem.

t------> // 1 tab

s....... // 7 spaces

Enter the Insert mode, put the cursor after the trailing tab or the trailing spaces, and press the Backspace key.

Here is how I would like it to work:

t // tab has been removed

s...... // 5 spaces

And here is how it actually works:

t..... // 5 spaces

s..... // 5 spaces

Of course, I can replace set shiftwidth=2 softtabstop=-1 with shiftwidth=2 softtabstop=8, but there will be another problem:

Instead of

t

s...... // 5 spaces

It will be

t

s

So my question:

How can I set up Vim so that...

• When I press >>, it will indent code with 2 spaces
• When I press Tab in Insert mode, it will insert the tab character
• When I press Backspace and there are spaces before it, Backspace should remove 2 spaces per keypress
• When I press Backspace and there are tabs before it, Backspace should remove 1 tab per keypress

Answer 1

As you described in your question, and as Matt confirmed in his answer, you cannot do this using only Vim's options.

We are, therefore, going to have to set up a mapping. There are several ways you could go about this, but here's how I'd do it:

set shiftwidth=2 softtabstop=0 noexpandtab
inoremap <expr> <BS> col('.') > 2 &&
  \ col('.') % 2 == 1 &&
  \ getline('.')[col('.') - 3:col('.') - 2] == '  '
  \ ? '<BS><BS>' : '<BS>'

This sets up an expression mapping so when you press Backspace it checks the text behind the cursor and backspaces twice if two spaces should be deleted.

N.B. You don't mention this in your requirements, but I made it only delete two spaces if the cursor is already at a multiple of 2. Because you have 'shiftround' set, this is how >> and << will work for you, so I thought you'd want Backspace to work in the same way. If you don't like this, you can delete the entire line \ col('.') % 2 == 1 &&.

Answer 2

1. When I press >>, it will indent code with 2 spaces

setlocal shiftwidth=2

2. When I press Tab in Insert mode, it will insert the tab character

setlocal noexpandtab

3. When I press Backspace and there are spaces before it, Backspace should remove 2 spaces per keypress

setlocal softtabstop=2

4. When I press Backspace and there are tabs before it, Backspace should remove 1 tab per keypress

setlocal softtabstop=0

Obviously, 3 and 4 are incompatible with each other. You may also try setlocal shiftwidth=2 softtabstop=0 smarttab. Then at start of line backspace counts as "2 spaces" while in the middle as "1 space or tab".