LaTeX3 Error: Backend request inconsistent with engine: using 'pdfmode'

[Scott Kostyshak]

On Mon, Feb 03, 2020 at 04:44:07PM +0100, Kornel Benko wrote:
> Am Mon, 3 Feb 2020 10:42:06 -0500
> schrieb Scott Kostyshak <skostysh at lyx.org>:
> 
> > On Mon, Feb 03, 2020 at 04:29:34PM +0100, Kornel Benko wrote:
> > > 
> > > This is for instance with examples/Presentations/Foils.lyx trying to use pdflatex.
> > > Same error witth lualatex.
> > > OTOH, if compiled first to dvi, also pdflatex and lualatex compile fine.  
> > 
> > For me the compilation with pdflatex works fine on master, but I have an
> > outdated TeX Live version (and I don't want to update right now since I
> > don't want to break compilations I need for work).
> > 
> > Remind me in a week or so if there is still a mystery and I can test on
> > an updated TL once I get my Virtual Box setup working again.
> > 
> > Scott
> 
> I hope, I don't forget. :)

I tested on an updated TL. Removing the custom class option dvips fixes
it. However, I'm not sure this is the right thing to do. In the inverted
tests, we have the following:

  # Comment by Jürgen Spitzmüller
  # The document requests the dvips graphics driver,
  # and of course this fails with any other backend.
  #
  # The document compiles if one sets the graphics driver to "Automatic"
  # and remove the dvips class option. But then, the output is not correct
  # (rotation of foils does not work).
  export/examples/(|fr/)Presentations/Foils_pdf[45]_systemF

The output does not seem to change with or without the option for pdf2
format, but the above comment suggests it does for other formats.

I don't know if the change in latex3 was intended. For example, here's a
related issue:

  https://github.com/latex3/latex3/issues/677
  https://tex.stackexchange.com/questions/529129/backend-inconsistent-error-when-using-xelatex-with-dvisvgm-backend

Does anyone know whether the change is intended or should we file a bug
report?

Scott
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