Re: Advice needed on modeline customization hack...

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 16 Apr 2017 18:57:40 -0400
> From: "Perry E. Metzger" <perry@piermont.com>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>, emacs-devel@gnu.org
> 
> Attached is an improved patch, including documentation changes.

Thanks.  Allow me a few comments below.

> Comments solicited. I'm not fond of the name
> "column-number-mode-starts-from-zero" by the way.

How about column-number-indicator-zero-based instead?

> +@vindex column-number-mode-starts-from-zero
> +  In Column Number mode, the displayed column number begins at zero at
> +the start of a line. If you would prefer for the displayed column
> +number to begin at one, you may set
> +@code{column-number-mode-starts-from-zero} to @code{nil}.

The first sentence is ambiguous with the current bidirectional
display, because "start of line" is ambiguous.  I suggest to use the
wording with which we describe current-column:

  ... the displayed column number counts from 0 at the left margin of
  the window.

I also think that using digits 0 and 1 is better than using the words,
but that's my personal preference, so if you feel strongly about using
words, I won't object.

Also, please leave 2 spaces between sentences, as we use the US
English conventions in our documentation.

>  @item %c
> -The current column number of point.
> +The current column number of point, starting from zero.
> +
> +@item %C
> +The current column number of point, starting from one.

I think "zero-based" and "one-based" is better.  Or maybe include a
more detailed description of how the column is counted.

Please also add a NEWS entry about this new option.

> diff --git a/lisp/simple.el b/lisp/simple.el
> index 5f70adedc4..821880b1f3 100644
> --- a/lisp/simple.el
> +++ b/lisp/simple.el
> @@ -7198,6 +7198,10 @@ column-number-mode
>  If called from Lisp, enable the mode if ARG is omitted or nil."
>    :global t :group 'mode-line)
>  
> +(defvar column-number-mode-starts-from-zero t
> +  "When set to true, Column Number mode displays columns starting from zero.
> +Otherwise, displayed column numbers start from one.")

This should be a defcustom, not defvar.  I think it's best to have it
in xdisp.c, where the feature is implemented, in which case you should
add the necessary stuff to cus-start.el to allow its customization by
Custom.

What about the required change to mode_line_update_needed?