Move to goal-column inserting spaces if necessary

Question

I have a bunch of lines of text and I'm trying to insert text starting at a certain column on each line. For example:

'Some text'            This is ok
'Another longer text'  ask Ram
'weird stuff'          see other file
'more lines'
'even more lines'

I'd like to continue typing text on the further lines, at the same column as the previous lines. The part that's cumbersome is moving to the right place on each line.

Emacs has a way of moving to the same place on each line: set-goal-column. This would work if that column already existed on each line, but that's not the case here.

One way I can work around this (which I'm actually using) is to insert a lot of spaces on each line (replace-regexp $ with a few dozen spaces), then C-x C-n (set-goal-column), and use regular C-n to move between lines. But I'd like to know whether there's a clean way of achieving something better: of setting things up so that after set-goal-column, I can just use C-n to move to the next line, and Emacs will automatically insert the appropriate number of spaces if there weren't enough columns to start with.

Answer 1

Here is advice that should do what you want:

(defun goal-column-advice (&rest _args)
  "Advice inserting spaces when needed to obey `goal-column'.

This advice is intended as :after advice for commands
`previous-line' and `next-line'.  Normally, these commands will
attempt to obey any `goal-column' setting, but only on lines that
are long enough that the `goal-column' is not past the end of the
line.  This advice changes the advised command to instead pad the
line with spaces in this circumstance.  If `goal-column' is nil,
the command behaves as if it were not advised."
  (when goal-column (move-to-column goal-column t)))

(advice-add 'previous-line :after #'goal-column-advice)
(advice-add 'next-line     :after #'goal-column-advice)

Thanks to @phils for the comment pointing out the role of move-to-column.

As @phils also notes, this method does leave trailing whitespace in your buffer, which some people may not want. The OP doesn't seem to mind, but others may need to find a different solution.

Answer 2

;; Here we create the concept of a 'tab-column.'
;; Set the tab column where you want by positioning the cursor and typeing M-+
;; Then move to another line and type M-=, and EMACS will insert enough spaces
;; to get you to the column. This is useful for alinging columns of text without tabs.
;; tab-column is a silly name; I need a better one.

(defun set-tab-column (&rest _args)
  "Sets tab column to current column"
  (interactive "P")
  (setq tab-column (current-column))
  (message "tab column set to %s" tab-column))
(global-set-key (kbd "M-+") 'set-tab-column)
(setq tab-column 0))

(defun space-to-tab-column (&rest _args)
  "Insert spaces to tab-column"
  (interactive "P")
  (let ((count 0))
    (while (> tab-column (current-column))
      (setq count (+ 1 count))
      (insert " ")
      )
    (message "%s spaces inserted" count)
    )
)
(global-set-key (kbd "M-=") 'space-to-tab-column)