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Re: Emacs's handling of line numbers [from bug#5042]

From: Mark Lillibridge
Subject: Re: Emacs's handling of line numbers [from bug#5042]
Date: Sun, 11 Apr 2010 15:22:21 -0700

[sorry for the delay replying]

Stefan wrote:
>  Mark wrote:
>  > (defcustom restart-numbering-restriction nil
>  >   "If true, lines inside a restriction are numbered starting from 1.
>  > If false, line numbers correspond to position inside the buffer."
>  >   :group 'editing-basics
>  >   :type  'boolean)
>  The problem is not one of line-numbers but of narrowing/restriction only
>  (which in turn has impacts on line-numbering among other things).
>  So I don't think "number" deserves to be part of the name.
>  While implementing it, please try and merge it with (AKA have it replace)
>  font-lock-dont-widen.
>  Of course, a better approach would distinguish the two kinds of
>  narrowing not on a buffer-basis but on a narrowing-basis, so that if you
>  interactively narrow to a portion of a page in an Info buffer, you
>  can still get line-numbers starting at the beginning of the page
>  (even if it's outside the narrowed portion).

    Hmmm.  I think some more design may be in order before implementing.
Let me try and sketch an idea based on the above:

* There are two (optional) levels of restriction: "semantic" and
  "temporary".  (better names anyone?)

* The temporary restriction is always contained in or the same as the
  semantic one.

* font-lock always uses the semantic restriction (font-lock-dont-widen
  goes away)

* By default, line numbering is also based on the semantic restriction
  * a global option allows switching this behavior to use the temporary
    restriction for line numbering.

* Rmail, Info, and the like, use the semantic restriction because the
  restricted-to-unit is effectively an independent buffer (semantic

* The default narrowing commands available to users use the temporary

Does this sort of approach make sense?  Do people like it?  It is a more
global change than I was originally envisioning.

- Mark

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