Sharing here a solution I was happy with:
```{r, eval=!is.null(df), ...}
this has the advantage of hiding the distracting edge case handling from
the expository code being shown to the vignette reader.
Mike C
On Thu, Jan 1, 2026, 4:53 PM Rafael H. M. Pereira <[email protected]>
wrote:
> Thank you all for the kind suggestions! Dirk's advice (in the same spirit
> of Hadely's suggestion) should work like a glove !
>
> For the record, I really appreciate how supportive the R community (and
> this group in particular) is. Thanks a bunch and happy New Year!
>
> best,
> Rafa Pereira
>
> On Tue, Dec 30, 2025 at 2:54 PM Hadley Wickham <[email protected]>
> wrote:
>
> > Or slightly simpler (if less helpful), you can do something like:
> >
> > if (is.null(df)) {
> > knitr::opts_chunk(eval = FALSE)
> > }
> >
> > Hadley
> >
> > On Mon, Dec 29, 2025 at 7:23 PM Michael Chirico <
> [email protected]>
> > wrote:
> >
> >> At a glance you might try a hidden code chunk that looks for NULL input
> >> and
> >> populates a "fake" dataset if so.
> >>
> >> On Mon, Dec 29, 2025, 4:35 PM Rafael H. M. Pereira <
> >> [email protected]> wrote:
> >>
> >> > Hi all,
> >> >
> >> > I would very much appreciate your thoughts on this situation.
> >> >
> >> > # context
> >> > I received an email from Prof Ripley saying that my package is not
> >> "falling
> >> > gracefully". Error report here
> >> > https://www.stats.ox.ac.uk/pub/bdr/Rblas/ATLAS/aopdata.out
> >> >
> >> > The error happens in the code below. You see, in the case of an
> internet
> >> > connection issue, the aopdata::read_population() function returns a
> >> silent
> >> > NULL plus an informative message, as it should. So my package does in
> >> fact
> >> > fail gracefully whenever an internet connection is unavailable.
> >> >
> >> > In this case, though, the error is actually happening in the ggplot2
> >> call.
> >> > Because the df object is NULL, ggplot2 cannot find the "P001" column.
> In
> >> > short, the package itself does follow CRAN's policy when there is an
> >> > eventual internet connection issue, but the subsequent code throws an
> >> error
> >> > in such a case.
> >> >
> >> > Given this behavior, I’m not sure there is a change I could make to my
> >> > package that would fully prevent this situation, other than removing
> >> > vignettes that demonstrate how to use the function outputs, which I
> >> would
> >> > prefer to avoid if possible.
> >> >
> >> > # the situation
> >> > When I asked for advice, a kind Cran maintainer said: "So it is not
> good
> >> > enough to have a function return NULL when the subsequent code will
> >> throw
> >> > an error when it gets that NULL."
> >> >
> >> > So here is the situation. The Cran Policy (see it below) requires *the
> >> > package* to fail gracefully. It does not mention subsequent code.
> Imho,
> >> it
> >> > should not require any subsequent code to fail gracefully. As a
> >> > package developer, I only have control over the functioning of my
> >> package,
> >> > I cannot control what code users will use to analyze the output of my
> >> > package functions.
> >> >
> >> > If necessary, I will simply not run the ggplot calls in my vignettes
> and
> >> > render pre-generated plots saved in .png. I feel this would be a bad
> >> > solution to keep the package on CRAN, though. I would really
> appreciate
> >> > your thoughts on this.
> >> >
> >> > best,
> >> > Rafael Pereira
> >> >
> >> > *Cran Policy asks that:*
> >> >
> >> > - Packages which use Internet resources should fail gracefully with
> >> > an informative
> >> > message if the resource is not available or has changed (and not
> >> give a
> >> > check warning nor error)
> >> >
> >> >
> >> > # code causing the error
> >> >
> >> > library(aopdata)
> >> > library(ggplot2)
> >> > df <- aopdata::read_population
> >> > <https://ipeagit.github.io/aopdata/reference/read_population.html>(
> >> > city = 'Fortaleza', year = 2010, geometry = TRUE, showProgress =
> >> > FALSE )
> >> >
> >> >
> >> >
> >> > ggplot() +
> >> > geom_sf(data=subset(df, P001>0), aes(fill=P001), color=NA,
> alpha=.8) +
> >> > scale_fill_distiller(palette = "YlOrRd", direction = 1)+
> >> > labs(title='Population distribution', fill="Total population") +
> >> > theme_void()
> >> >
> >> >
> >> > best,
> >> > Rafael Pereira
> >> >
> >> > [[alternative HTML version deleted]]
> >> >
> >> > ______________________________________________
> >> > [email protected] mailing list
> >> > https://stat.ethz.ch/mailman/listinfo/r-package-devel
> >> >
> >>
> >> [[alternative HTML version deleted]]
> >>
> >> ______________________________________________
> >> [email protected] mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-package-devel
> >>
> >
> >
> > --
> > http://hadley.nz
> >
>
> [[alternative HTML version deleted]]
>
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