# Package Development with renv

## Development

Often, R packages will have other R packages as dependencies. For this, one must declare their R package dependencies within the package `DESCRIPTION` file. If you want to prepare your environment for package development, you can use:

    renv::install()

to install the packages as declared in the package’s `DESCRIPTION` file. This action is roughly analogous to `remotes::install_deps()`.

If you’re developing a package that you intend to release to CRAN, then you likely want to build and test your package against the latest versions of your dependencies as available on CRAN. For this, you should consider using:

    renv::update()

to ensure your package dependencies are up-to-date, as appropriate.

## Isolation

Normally, a package under development should be tested against the latest-available versions of its dependencies on CRAN. However, in some cases, you may need to ensure your package is compatible with other packages also currently under development.

In these cases, the `renv` project library can be useful – you can install the development version(s) of your dependencies into the project library, without worrying about clobbering any packages already installed in your user library.

In these cases, you can declare your development dependencies using the `Remotes` field of the `DESCRIPTION` file; e.g.

    Remotes:
      r-lib/ggplot2

and `renv::install()` will parse that remotes declaration and retrieve the requested package. See the `remotes` vignette, Dependency resolution for R package development, for more details.

## Testing

While developing your package, you may want to use a continuous integration service (such as Travis CI) to build and test your package remotely. You can use `renv` to help facilitate this testing – see the Continuous Integration vignette for more information. In particular, clever use of the `renv` cache can help save time that might normally be spent on package installation.

## R CMD build and the Project Library

By default, when building a package tarball, R will copy all files within the package directory to a temporary build directory before building the package. Unfortunately, this also implies copying the `renv` library. When that library is large, this can dramatically increase the amount of time it takes to build your package.

One way to resolve this issue is to force `renv` to use a library path that lives outside of your project. For example, you might set the following in a start-up `.Renviron` file:

    RENV_PATHS_LIBRARY_ROOT = ~/.renv/library

`renv` will then form library paths within this directory.