bug#34038: 26.1; set-window-start sometimes fails to set window start

[Markus Triska]

martin rudalics <rudalics@gmx.at> writes:

>> In this snippet, I try to restore the exact same configuration that you
>> see when "Step 1 ..." is displayed, i.e., window-start is set so that
>> point is on the very first line, which is blank. When you press a key at
>
> I think you mean on the very _last_ line here.  Right?

I mean point is at the first line that is shown in the window, i.e.,
point is at the topmost left position in the window, and yes, that is
the last line of the buffer.

> in an empty *scratch* buffer here gives 97..97 and 393..97 for (point)
> and wp.  Do you see that?

I get:

    Step 1 at 79 wp is 79
    Step 2 at 321 wp is 79

where (frame-height) yields 30, and (window-height) yields 29.

> If so then does (setq scroll-conservatively 101) fix it?

Yes, with scroll-conservatively set to 101, I get the intended effect,
i.e., the same position of window point as after Step 1 (79) also after
the whole form is evaluated! This is what I expect also with the default
settings, i.e., scroll-conservatively set to 0, for this snippet.

Thank you and all the best,
Markus