Re: "Soft" indent with visual-line-mode?

[Stephen Berman]

On Fri, 09 Dec 2011 15:25:22 -0500 Tim Stewart <tim@stoo.org> wrote:

> On 09/11/09 08:58 AM, Stephen Berman wrote:
>> On Wed, 9 Sep 2009 13:53:58 -0400 Tim Stewart<tim@stoo.org>  wrote:
>>
>>> Hello Emacs Help,
>>>
>>> I like the idea of using longlines-mode or visual-line-mode to spend less 
>>> time
>>> formatting code as I write.  However, it is not useful to me  when the 
>>> wrapped
>>> lines start in the first column and break up the flow  of the code.
>>>
>>> As an example, this is what I get now with a line that is indented 4 spaces.
>>> This is all one line, wrapped by the editor for me:
>>>
>>>      This is a test of the emergency broadcast system.  This is only a 
>>> test. In
>>> the event of a real emergency, your head would have exploded.
>>>
>>> And this is what I want:
>>>
>>>      This is a test of the emergency broadcast system.  This is only a 
>>> test. In
>>>      the event of a real emergency, your head would have exploded.
>>>
>>> I've heard this referred to as a "soft" indent.  I believe that Visual
>>> SlickEdit 9 and Kate both support this feature if you'd like other  
>>> examples.
>>>
>>> Does anyone know of a feature or add-on for Emacs that can accomplish this?
>>> I've scoured the 'Tubes and can't find anything.
>>
>> The following code might do what you want, though it might need some
>> tweaking.  (To use it, evaluate it and call the minor mode manually or
>> add it to appropriate mode hooks.)
>>
>> Steve Berman
>>
>> (defun srb-adaptive-indent (beg end)
>>    "Indent the region between BEG and END with adaptive filling."
>>    (goto-char beg)
>>    (while
>>        (let ((lbp (line-beginning-position))
>>          (lep (line-end-position)))
>>      (put-text-property lbp lep 'wrap-prefix (fill-context-prefix lbp lep))
>>      (search-forward "\n" end t))))
>>
>> (define-minor-mode srb-adaptive-wrap-mode
>>    "Wrap the buffer text with adaptive filling."
>>    :lighter ""
>>    (save-excursion
>>      (save-restriction
>>        (widen)
>>        (let ((buffer-undo-list t)
>>          (inhibit-read-only t)
>>          (mod (buffer-modified-p)))
>>      (if srb-adaptive-wrap-mode
>>          (progn
>>            (setq word-wrap t)
>>            (unless (member '(continuation) fringe-indicator-alist)
>>              (push '(continuation) fringe-indicator-alist))
>>            (jit-lock-register 'srb-adaptive-indent))
>>        (jit-lock-unregister 'srb-adaptive-indent)
>>        (remove-text-properties (point-min) (point-max) '(wrap-prefix pref))
>>        (setq fringe-indicator-alist
>>              (delete '(continuation) fringe-indicator-alist))
>>        (setq word-wrap nil))
>>      (restore-buffer-modified-p mod)))))
>
> It took me quite a while to try this.  Thank you Steve, it works quite well!
> It was a little odd in Emacs Lisp mode, but seems to work great in more
> block-oriented code like Python, C, Perl, etc.
>
> I also added the following to make it easy to enable globally and I tucked it
> away in my load-path as srb-adaptive-wrap-mode.el:
>
>
> (defun turn-on-srb-adaptive-wrap-mode ()
>   (srb-adaptive-wrap-mode 1))
>
> (define-globalized-minor-mode global-srb-adaptive-wrap-mode
>   srb-adaptive-wrap-mode turn-on-srb-adaptive-wrap-mode
>   :lighter "")
>
> (provide 'srb-adaptive-wrap-mode)
>
>
> I also turn on the gutter arrows to make it more obvious what's happening:
>
>
> ; Let's show the fringe indicators when in visual-line-mode
> (setq visual-line-fringe-indicators
>        '(left-curly-arrow right-curly-arrow))
>
>
> Thanks again!
>
> -TimS

Glad you find it useful.  FYI, in the mean time a cleaner version has
been added to the GNU Emacs Lisp Package Archive (ELPA) as
adaptive-wrap-prefix.el.  This version leaves the fringe indicators
alone. (I removed them in my original version for aesthetic reasons, but
Stefan Monnier (who improved the code) pointed out that that's an
independent feature.)  You can download it via `M-x list-packages' (or
via the menu: Options->Manage Emacs Packages), or directly from this
URL:

http://bzr.savannah.gnu.org/lh/emacs/elpa/files/head:/packages/adaptive-wrap-prefix/

Steve Berman