Re: cursor-intangible and rear-nonsticky t

[JD Smith <jdtsmith@gmail.com>]

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> On Apr 5, 2021, at 12:47 PM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
> 
>> If '(rear-nonsticky t) is among the text properties, the
>> `pre-redisplay-functions' do not apparently get called, and so
>> 'cursor-intangible fails to function.  
> 
> I don't think that's really what happens.  I suspect the issue comes
> from the difference between `get-pos-property` and `get-char-property`:
> positions (like `point`) are not placed on a character but between two
> characters.  But text properties only apply to characters.  So the
> properties that are "on a position" are based on what properties would
> a character inherit if it where inserted at that position.
> 
> By default text properties are front-nonstick and rear-sticky, so
> basically a position gets its properties from the char right before it.
> But if you set (rear-nonsticky t), then you get no properties at all at
> that position.
> 
> So, I suspect that you're applying (rear-nonsticky t) a bit too
> generously, e.g. to all the chars in the prompt rather than only to the
> last one.

Interesting, so `rear-nonsticky t` is rather powerful in suppressing text-properties within contiguous text.  

I believe `comint-output-filter` is the one responsible for setting `rear-nonsticky t` across the entire prompt:

	    (let ((prompt-start (save-excursion (forward-line 0) (point)))
		  (inhibit-read-only t))
             ...
	      (add-text-properties prompt-start (point) '(rear-nonsticky t)))


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