FoldingCommands

Add for example in your user init.lua or in a separate module:

-- Indent Folding
function collapse_fold(line)
  local line = line or buffer:line_from_position(buffer.current_pos)
    if buffer.fold_expanded[line] and buffer.line_visible[line] then
      buffer:toggle_fold(line)      -- colapse fold
      if not buffer.line_visible[line] then
        buffer:goto_line(buffer.fold_parent[line]) --set caret on parent fold line
      end
    end
end

function expand_fold(line)
  local line = line or buffer:line_from_position(buffer.current_pos)
  if not buffer.fold_expanded[line] and buffer.line_visible[line] then
    buffer:toggle_fold(line)
    buffer:goto_line(line+1) --set caret on the first child line of the fold
  end
end

function collapse_folds()
  for i = 1, buffer.line_count do
    collapse_fold(i)
  end
end

function expand_folds()
  for i = 1, buffer.line_count do
    expand_fold(i)
  end
end

keys['alt+right'] = expand_fold
keys['alt+left'] = collapse_fold
keys['ctrl+alt+right'] = expand_folds
keys['ctrl+alt+left'] = collapse_folds

Immediate testing of changes can be done with F2 (To get a textadept command prompt) and the issue the command reset().