On Sun, 29 Oct 2017 16:07:34 +0200, Eli Zaretskii wrote:
> Thanks, this bug was introduced by 9eb028f, and the problematic
> property is 'display' with value '(space :align-to (NNN))'.  It
> causes shr-fill-line to infloop when this property is put on a
> newline.

Sorry, I did the 9eb028f change for fixing bug#24034:
<https://lists.gnu.org/archive/html/bug-gnu-emacs/2016-07/msg01042.html>

> I can prevent the loop with the patch below.  I'm not sure this is the
> right fix, though.  Comments?

That's ok, but the properties necessary to copy there are only
`face' and `image-displayer'.  How about this one?

* lisp/net/shr.el (shr-fill-line): Copy only face and image-displayer
properties to gaps (bug#29047).