Compatibility with ggplot2 4.0.0

[teunbrand]

Hi Winston & team,

We're preparing a new release of ggplot2 and found a reverse dependency failure for shiny.
Because we're switching from S7 to S3 in this release, an S3 method in your tests needed a small adjustment to work for the S7 class.

Best wishes,
Teun

[wch]

@teunbrand Thanks for the PR! When are you planning on the ggplot2 release?

I wonder if the CRAN releases will have to be coordinated -- that could make things more complicated. Would it make sense to make the test conditional on ggplot2 version?

[teunbrand]

When are you planning on the ggplot2 release?

I expect in 3 weeks or later. We're now tinkering to prevent unnecessary revdep failures, but we undoubtedly can't prevent all and have to give 2 weeks notice to maintainers.

Would it make sense to make the test conditional on ggplot2 version?

That is probably not necessary. The change in this PR would work with both the old and the new. Once shiny fully depends on ggplot2 >= 4.0.0 you can remove the print.ggplot <- from this line.