bug#67791: 30.0.50; `t' command on Gnus summary buffer sometimes causes an error

[Eli Zaretskii]

> Date: Tue, 12 Dec 2023 11:15:54 +0900
> From: Katsumi Yamaoka <yamaoka@jpl.org>
> 
> Because the `gnus-article-treat-fold-headers' function does not
> work as expected.  `t' command, i.e. `gnus-summary-toggle-header'
> is invoked on the Gnus summary buffer, that runs by default
> `gnus-article-treat-fold-headers' by way of `gnus-treat-article'.
> It works on the article buffer and folds headers with the help of
> the pixel-fill functions.  One of them, `pixel-fill-region' uses
> the built-in `window-text-pixel-size' function, that is required
> to run on the selected window in which there is the text to
> measure the pixel size (since `pixel-fill-region' passes nil to
> `window-text-pixel-size' as the 1st argument `WINDOW').
> ,----
> | (window-text-pixel-size &optional WINDOW FROM TO ...)
> |
> | Return the size of the text of WINDOW's buffer in pixels.
> | WINDOW must be a live window and defaults to the selected one.
> `----
> Therefore, the window should be that of the article.  However,
> in that situation the selected one is that of the summary, as
> mentioned above.  Because of this, the `window-text-pixel-size'
> sometimes returns a funny value and it causes the error like
> this:
> 
> Debugger entered--Lisp error: (error "The indentation (640) is wider than 
> th...
>   signal(error ("The indentation (640) is wider than the fill width 
> (623)"))...
>   error("The indentation (%s) is wider than the fill width (%s)" 640 623)...
>   (progn (error "The indentation (%s) is wider than the fill width (%s)" 
> ind...
>   (if (> indentation pixel-width) (progn (error "The indentation (%s) is 
> wid...
>   (let ((indentation (car (window-text-pixel-size nil 
> (line-beginning-positi...
>   (save-excursion (goto-char start) (let ((indentation (car 
> (window-text-pix...
>   pixel-fill-region(101 181 623)
>  [...]
>   command-execute(gnus-summary-toggle-header)
> 
> Another possible cause might be the recent change (33b6de7a)
> made in `window-text-pixel-size', because such an error doesn't
> look to cause in Emacs 29.1.90 (the function before the change
> might possibly have worked on the current buffer, not the
> selected window).

Did you try using the newer buffer-text-pixel-size instead?