How to transform this Vimscript into Lua?

Question

Can anyone help me transform this into nvim.lua?

inoremap <silent><expr> <TAB>
    \ pumvisible() ? "<C-n>" :
        \ <SID>check_back_space() ? "<TAB>" : coc#refresh()

function! s:check_back_space() abort
    let cpos = col('.') - 1
    return !cpos || getline('.')[cpos - 1]  =~# '\s'
endfunction

What I've done:

local EXPR_NOREF_NOERR_TRUNC = { expr = true, noremap = true, silent = true, nowait = true }

vim.api.nvim_set_keymap('i', '<Tab>', 'check_back_space() ? "<C-n>" : "<Tab>"', EXPR_NOREF_NOERR_TRUNC)

But I don't know what's the function in lua to get the char at left of the currnet cursor pos.

Answer 1

:h nvim_win_get_cursor() will return a tuple containing the current cursor position, which you'll have to unpack to use. It takes an argument {window}, and you can use 0 to specify the current window.

:h nvim_get_current_line() is the Neovim Lua analog to getline('.').

Here is an example:

function check_back_space()
    -- get row and column
    local row, col = unpack(vim.api.nvim_win_get_cursor(0))
  
    -- get current line of text
    local linetext = vim.api.nvim_get_current_line()

    return col == 0 or string.match(linetext:sub(col, col), '%s') ~= nil
end

It's important to note the the column returned from nvim_win_get_cursor() is 0-based, while Lua arrays and col() are 1-based. So, in the following line

return col == 0 or string.match(linetext:sub(col, col), '%s') ~= nil

the first condition tests if col is the first column, and the second tests that the character in the previous column is white space, even though both use col.

---

See also:

• :h col()
• :h getline()
• Lua builtinstring.match