bug#33532: 26.1; set-window-configuration does not restore display start

[Markus Triska <triska@metalevel.at>]

Eli Zaretskii <eliz@gnu.org> writes:

> How important is the use case of replacing buffer text with identical
> text?  Because replacing with a different text will make preserving
> window-start position based on its numerical value not really a
> sensible thing, would it?  It could even be impossible, e.g. if the
> same position happens to be in the middle of a sequence of composed
> characters.

Please consider a use case that is described in the Emacs manual:

    In order to store a window configuration on disk and
    read it back in another Emacs session ...

In such use cases, I want to restore the exact same text in all buffers,
and then restore the window configuration, including display starts.

In fact, the snippet illustrates an even simpler situation: It stores
the configuration in a variable, and the session keeps running.  I would
like to obtain the configuration, then close all buffers, and later
restore their contents (for example, from files), and then use
set-window-configuration to restore the original window configuration,
including all window-starts.

Could set-window-configuration be generalized to reliably restore the
window-starts also in such cases? If not, please consider adjusting the
documentation to make clear what this actually guarantees. In
particular, when are window-starts reliably restored, and when not?

Thank you and all the best,
Markus