Cannot install CRAN dependencies from user-named repo

[jmcphers]

System details

RStudio Edition : Both
RStudio Version : 1.2.1293, 1.1.463

Steps to reproduce the problem

1. Remove all RStudio repository settings, so that getOption(repos) returns NULL in a new R session.
2. Remove the rmarkdown package.
3. Ensure that it is not possible to install packages from the RStudio global CRAN mirror.
4. Set a custom repo with a custom name (not CRAN) in your .Rprofile, such that getOption(repos) returns the named character my repo "https://my/repo/url"
5. Start a new R session.
6. Attempt to create an R notebook.

Describe the problem in detail

You are prompted to install the rmarkdown package. However, when RStudio attempts to do so, it tries to install from RStudio's global CRAN mirror (not the repo you set), and fails.

This happens because of an asymmetry in dependency checking and dependency installation. The dependency manager assumes the first repo is a CRAN mirror when it is checking to see if packages are available (see #1762).

rstudio/src/cpp/session/modules/ModuleTools.R

Lines 158 to 160 in b171b1a

	# if no repo named "CRAN", blindly guess that the first repo is a CRAN mirror
	if (length(repo) < 1 || is.na(repo)) {
	repo <- as.character(repos[[1]])

However, when packages are installed, we only use a mirror named CRAN, or the CRAN mirror in the user's settings.

rstudio/src/cpp/session/modules/SessionDependencies.cpp

Lines 352 to 353 in b171b1a

	cmd += "utils::install.packages(c(" + pkgList + "), " +
	"repos = '"+ module_context::CRANReposURL() + "'";

Describe the behavior you expected

If RStudio is willing to use a repo as a CRAN mirror when detecting available packages for dependency installation, it should also be willing to use that repo to actually install the packages.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs, per https://github.com/rstudio/rstudio/wiki/Issue-Grooming. Thank you for your contributions.

[stale]

This issue has been automatically closed due to inactivity.