Re: lib/56224: libcurses: adding character to last line of non-scrolling window wraps instead of

[Brett Lymn <blymn%internode.on.net@localhost>]

On Thu, Jun 10, 2021 at 03:55:02AM +0000, Michael Forney wrote:
>  
>  Thanks for the patch, I can confirm that this does solve the issue
>  for the application in question (catgirl).
>  

Excellent, that is a good start.

>  
>  1. It seems that now the string is truncated by one extra character
>  (the last column is empty). Since this last character doesn't extend
>  beyond the end of the line, my expectation is that it should not
>  be truncated. And indeed, this is how it behaves in ncurses.
>  

OK, I will fix that - my checks must be off by one.

>  2. I was thinking that this needed to be fixed in _cursesi_addwchar,
>  not _cursesi_addwbytes. Otherwise, addwstr and addch at the last
>  column still wrap to column 0 (though, addwstr already truncates
>  since it returns on the first ERR, whereas _curses_waddbytes ignores
>  all errors except for the last character).
>  

No, _cursesi_addwchar is used by other routines that really should be
inheriting the same behaviour, rather than fix each one individually I
went for fixing it in the common routine so they all behaved the same.
I think addwstr is the outlier in this instance.  I will look at fixing
that.

>  3. This seems incorrect to me:
>  

Yes, it is.  My bad.  I will rework that.  That probable explains why
the wide char version of the slk test failed after my updates.

>  
>  Below is an alternative fix I've been testing that seems to solve
>  these problems. The first thing it does is make _cursesi_waddbytes
>  break from the loop and return ERR when any of the _cursesi_addwchar
>  calls returns ERR (not just the last one). This is consistent with
>  waddnwstr. The second thing it does is delay wrapping the cursor x
>  position back to zero until after we return ERR if scrolling is not
>  allowed.
>  

I may have read the SUSv2 section on the scrolling behaviour incorrectly
but my interpretation is that trying to add a string at the bottom of
the screen that would cause a scroll when scrollok is false should
result in a silent truncation not ERR which is why I did what I did.
The effect of my change is a slk routine that used to strangely return
ERR no longer does so... I would like to keep that behaviour :)

The patch you have proposed does not look right, with your fix you will
have possibly not reset x to 0 but ISPASTEOL will be unset so the unset
of the ISPASTEOL flag needs to be moved too which does make some sense
to have that after a possible error return.  I will have a look at doing
that.

-- 
Brett Lymn
--
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