bug#24109: 24.5; Long lines in message mode make Emacs irresponsive

[Yuri D'Elia <wavexx@thregr.org>]

On Tue, Aug 30 2016, Eli Zaretskii <eliz@gnu.org> wrote:
>> The backtrace is as follows:
>> [...]
>
> I see nothing abnormal in the backtrace, at least not at a glance.
>
>> Emacs is stuck in try_window calling display_line, where the "it" parameter remains constant.
>
> What do you mean by "it parameter remains constant"?  That is a large
> structure; what parts of it remain constant?

The address of the structure remains constant (that is, display_line is
called with the same pointer). I don't know if this is expected to
change or not. I didn't actually compare the contents between calls.

>> I'm attaching the output of *it in the email, hoping it might be useful.
>
> Thanks, but it by itself doesn't help enough.  I need to see the text
> that Emacs is trying to display, at least.

This is hard to do. I tried to simply copy the text to another buffer in
trying to reproduce the problem, but I couldn't. It might be due some
overlays or properties.

Is there some way to conveniently dump the entire buffer state to a file
so we can debug this by reloading the content without having the mail
client in the way?

There's a lot of customization in the way which is making this harder
than it should be.