[XeTeX] Problem with ifpdf switch

[Julian Bradfield]

On 2020-07-06, John Was <johnoxuk at gmail.com> wrote:
> On acquiring a new PC I decided to install the latest TeXLive (previously I
> was on the 2013 version).  I use plain XeTeX.  To my surprise, the first
> page now has at the top the text:
>
> ifpdf [2016/04/04 v3.0 Provides the ifpdf switch]
>
> See the attached one-page PDF.
>
> Below I give some lines from my log file - it's the last line that is of
> interest, viz.:

No, that's not the line of interest. The lines of interest are all the
other files you might have loaded that might cause this breakage.
The line you see is, naturally, coming from ifpdf.sty, and to see it,
something must have broken the \ProvidesPackage, messed with catcodes,
or done something else to cause the break, unless the (rather old)
ifpdf.sty itself is buggy, which seems unlikely.

Please construct a minimal (non-)working example, and post the full
log file, with links to all non-standard files loaded.

Unless of course somebody jumps in to say they recognize the problem!