On 03/29/2018 04:11 AM, Eli Zaretskii wrote:
> I'd suggest, for a good measure, to have a variable which would force
> the conversion to floats, avoiding an error even without the trailing
> period.  We can later remove that variable, or make it a no-op, if the
> danger of breaking existing code turns out low or non-existent.

OK, I did that, by installing the attached into master, after installing 
the proposed patch.

As a result, unless the user sets the new variable 
read-integer-overflow-as-float, the Lisp reader now rejects the program 
(format "%x" 2738188573457603759) by signaling an overflow error. As 
this was the basis of the original bug report, I'm marking the bug as done.