Lint `"pkg" %in% installed.packages()`

[Bisaloo]

lintr::lint(
  text = '"pkg" %in% installed.packages()', 
  linters = lintr::all_linters()
)
#> ℹ No lints found.

^{Created on 2025-09-16 with reprex v2.1.1}

installed.packages() can be pretty slow, as noted in the documentation:

This needs to read several files per installed package, which will be slow on Windows and on some network-mounted file systems.

It will be slow when thousands of packages are installed, so do not use it to find out if a named package is installed (use find.package or system.file) nor to find out if a package is usable (call requireNamespace or require and check the return value) nor to find details of a small number of packages (use packageDescription).

And the recommended way to test for package availability should be requireNamespace("pkg", quietly = TRUE).

[Bisaloo]

Probably at the beginning at least, it's safer to restrict this to string literals on the left-hand side to allow the specific case when people want to test for the availability of multiple packages.

installed.packages() might still not be the best solution but we can't robustly test this via static analysis.

[MichaelChirico]

Sounds reasonable. I do worry about risk of false positives -- obviously there is some good use for installed.packages().

Would you mind sharing some good examples you find "in the wild" here?

BTW, in your title you use "pkg" %in% installed.packages(), which is definitely wrong vs. "pkg" %in% rownams(installed.packages()), is the latter what you meant? I do see a lot of people making the former mistake: https://github.com/search?q=lang%3AR+%2F%25in%25%5Cs*installed%5C.packages%5C%28%5C%29%5B%5E%5C%5B%5D%2F&type=code

[Bisaloo]

Yes, I noticed the incorrect "pkg" %in% installed.packages() in some examples. But by this I also meant linting "pkg" %in% installed.packages()[, 1] and "pkg" %in% installed.packages()[, "Package"] which are frequent alternatives to "pkg" %in% rownames(installed.packages()):

https://github.com/search?q=lang%3AR+%2F%25in%25%5Cs*installed%5C.packages%5C%28%5C%29%5C%5B%5Cs*%2C%5Cs*%281%7C%5B%22%27%5DPackage%5B%22%27%5D%29%5C%5D%2F&type=code

---

The function that prompted this issue:

https://github.com/Bioconductor/ExperimentHub/blob/f2a82b504abea3cf7eb9806afc5c12229a5c3e70/R/ExperimentHub-class.R#L90-L114