scopes-indent.lua

local function search_previous_lines(pattern)
  return vim.fn.search(pattern, 'znbW')
end

local block_starting_keywords = {
  'if',
  'else',
  'elseif',
  'then',
  'case',
  'pass',
  'default',
  'except',
  'fn',
  'fn\\.\\.\\.',
  'inline\\.\\.\\.',
  'sugar',
  'spice',
  'inline',
  'label',
  'do',
  'embed',
  'try',
  'loop',
  'for',
  'fold',
  'while',
  'spice-quote',
  'enum',
  'struct',
  '::',
  'static-if',
  'sugar-if',
}

local block_ending_keywords = {
  'return',
  'break',
  'repeat',
  'continue',
  'merge',
}

local function re_or(items)
  return ('\\(%s\\)'):format(table.concat(items, '\\|'))
end

local block_start_pattern = re_or { '^ *' .. re_or(block_starting_keywords) .. re_or { ' ', '$' }, re_or { '=', ':=' } .. ' *$' }
local block_start_regexp = vim.regex(block_start_pattern)

local block_end_pattern = '^ *' .. re_or(block_ending_keywords) .. re_or { ';', '\\s\\+\\S\\+.*' } .. '$'
local block_end_regexp = vim.regex(block_end_pattern)

local blank_line_regexp = vim.regex '^ *$'

local indent = vim.fn.indent
local getline = vim.fn.getline

local function scopes_indent_algorithm()
  local line_number = vim.v.lnum
  local prev_line_number = search_previous_lines '[^ \\n]'
  -- if at the start of the file (no prior non-blank lines), indent to the beginning of the line
  if prev_line_number == 0 then
    return 0
  end

  local cur_line = getline(line_number)
  local prev_line = getline(prev_line_number)
  local prev_indent = indent(prev_line_number)
  local cur_indent = indent(line_number)
  local is_blank_line = not not blank_line_regexp:match_str(cur_line)
  local max_indent = prev_indent + 4
  local next_alignment = cur_indent + (4 - (cur_indent % 4))
  local is_aligned = cur_indent + 4 == next_alignment

  -- are we reindenting a line?
  if not is_blank_line then
    if cur_indent >= max_indent then
      return max_indent
    elseif is_aligned then
      return cur_indent + 4
    else
      return next_alignment
    end
  -- entirely new line
  elseif cur_indent == 0 then
    if block_start_regexp:match_str(prev_line) then
      return max_indent
    elseif block_end_regexp:match_str(prev_line) then
      return math.max(0, prev_indent - 4)
    else
      return is_aligned and math.min(prev_indent, cur_indent + 4) or next_alignment
    end
  -- adjusting new line
  else
    return is_aligned and math.min(max_indent, cur_indent + 4) or next_alignment
  end
end

return {
  scopes_indent_algorithm = scopes_indent_algorithm,
}