r-cran-* binaries fail to install when specifying R version in runtime.txt

Bug description

Using R buildpack: when specifying r-3.6-2019-09-24 in runtime.txt installing r-cran-* binaries using apt.txt fails.

Error references wrong R version r-api-3.4 which is usually installed with r-base-core. Possibly related to #813.

Expected behaviour

r-cran-* binaries install with all dependencies.

Actual behaviour

Install fails with error output (from mybinder.org and locally with latest repo2docker). This example tries to install r-cran-crosstalk but also fails with any other binary:

Step 55/71 : RUN apt-get -qq update && apt-get install --yes --no-install-recommends r-cran-crosstalk && apt-get -qq purge && apt-get -qq clean && rm -rf /var/lib/apt/lists/*
 ---> Running in 46e19b8d69df
Reading package lists...
Building dependency tree...
Reading state information...
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 r-cran-crosstalk : Depends: r-api-3.4
                    Depends: r-cran-htmltools (>= 0.3.5) but it is not going to be installed
                    Depends: r-cran-jsonlite but it is not going to be installed
                    Depends: r-cran-lazyeval but it is not going to be installed
                    Depends: r-cran-r6 but it is not going to be installed
                    Depends: r-cran-shiny (>= 0.11) but it is not going to be installed
                    Depends: r-cran-ggplot2 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
Removing intermediate container 46e19b8d69df
The command '/bin/sh -c apt-get -qq update && apt-get install --yes --no-install-recommends r-cran-crosstalk && apt-get -qq purge && apt-get -qq clean && rm -rf /var/lib/apt/lists/*' returned a non-zero code: 100

How to reproduce

1. Example repo.
2. Or
3. Or

jupyter-repo2docker --ref origin/minpro --no-run --debug https://github.com/brooksambrose/studio

Your personal set up

• mybinder.org

[betatim]

Using https://cran.r-project.org/bin/linux/ubuntu/README.html#administration-and-maintances-of-r-packages brings us back to #813

I think https://launchpad.net/~marutter/+archive/ubuntu/c2d4u is different from the PPA described on https://cran.r-project.org/bin/linux/ubuntu/README.html. The maintainers from the latter said on their mailing list that only the latest version of R is supported by their PPA. I couldn’t find any documentation for the c2d4u PPA regarding which versions of R they support and for how long.

I don’t think we will be letting users add custom PPAs. It feels like a lot of them make very specific assumptions about who you are/what you are doing. Also it seems they tend to be “rolling” in terms of the versions they provide which makes it hard to write a spec for a container now that will still work in a few releases (of the PPA) time.

[brooksambrose]

Reading more about community practice, this should be possible with arbitrary versions of ubuntu and/or R using ppa:marutter/c2d4u as explained for example:

• https://cran.r-project.org/bin/linux/ubuntu/README.html#administration-and-maintances-of-r-packages
• https://youtu.be/qIjWirNma-8?t=90
• https://github.com/rstudio/shinyapps-package-dependencies/issues/4

You and @cboettig were also discussing this last year https://github.com/jupyter/repo2docker/issues/412#issuecomment-443409982, so wondering if adding the PPA is more possible now since r2d had evolved?