GNU bug report logs - #32777
27.0.50; window-buffer gets wrong point

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From: Federico Tedin <federicotedin <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 32777 <at> debbugs.gnu.org, juri <at> linkov.net
Subject: bug#32777: 27.0.50; window-buffer gets wrong point
Date: Tue, 2 Oct 2018 09:31:25 -0300

> Can you explain the change?  The minibuffer window is already the
> selected window at this point (look at the implementation of
> minibuffer-selected-window), so using with-selected-window, which
> seems to be the only real change in the above, should be redundant.

This was my reasoning:

Calling "minibuffer-selected-window" returns the last selected window
before switching to the minibuffer. Then, calling "window-buffer" with
that window will return that window's buffer.

The problem is that when "with-current-buffer" is called with the
resulting buffer, it that buffer has been opened on more than one
window, the active window will be set according to a criteria which I
haven't figured out yet, but not necessarily to the same exact window
"minibuffer-selected-window" returned.

The way I tested this was the following:
1) On a frame, open three windows. On the first two, open *scratch*.
On the third one, open
any other buffer.
2) Insert some content into buffer *scratch* ("hello").
3) Make sure the first window is selected, and move the point to (point-min).
4) M-x eval-expression (with-current-buffer "*scratch*" (message "%s"
(point))) should yield "1".
5) Select the second window, and move the point to (point-max).
6) M-x eval-expression (with-current-buffer "*scratch*" (message "%s"
(point))) should yield "7".
7) Now, select the third window.
8) M-x eval-expression (with-current-buffer "*scratch*" (message "%s" (point)))

The last point yields "1" in my case. If I wanted it to yield "7", I
would have to explicitly select the second window.  So from this, I
reasoned that using M-n when in read-extended-command, it will try to
read a command from the last selected window's buffer, but the value
of the point can vary if there's more than one window visiting that
buffer (like in the test case originally described by Juri). Please
correct me if I'm wrong.

> Also, with-selected-window makes the window's buffer current, so why
> did you need with-current-buffer in addition?  What am I missing?

This was an oversight on my part.

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