bug#3400: bug in add-text-properties

[martin rudalics]

> Hmm.  If I have
>
>    12345
>    ABCDE
>
> and I make `12345' + the newline after the `5' invisible and
> intangible, I see
>
>   ABCDE
>
> in the buffer.  If the blinking cursor stays on the `A', and you press
> `C-x =', do you *really* expect to see the properties of character `1'
> instead of `A'?  This is completely counterintuitive IMHO.

Then the value of `point' at the time you invoke that command is
counterintuitive.

>> So IMHO this is not a bug in `add-text-properties'.
>
> Maybe.  I don't know the internal details of Emacs.  However, calling
> add-text-properties triggers the problem I experience.
>
>> It's arguable whether point should be allowed to be there in your
>> case,
>
> In this particular case I don't care where `point' is.  I want to get
> the correct result of `C-x ='.

Don't blame `describe-char' here.  It must be able to work on any buffer
position including those preceded and/or followed by invisible text.

>> but then where to move point when the entire buffer is invisible?
>
> This might be handled as a special case.

Maybe.  But then you admit that the problem is with the position of
`point' ;-) Anyway, IIRC the idea was that you should be able put a
visible overlay before invisible text at the beginning of the buffer and
be able to move the cursor there.  I have no idea whether that ever
worked, though.

>>> A side effect is that `C-a' no longer moves to the beginning of the
>>> line.
>> A side effect of what?
>
> Of calling add-text-properties as described in my report.  I do expect
> that C-a moves the blinking cursor to the beginning of the line and
> not to the *second* character in the buffer, letter `B'.

This _is_ a bug and I doubt it's the only one with respect to moving
point over invisible text.

martin