# Package development

## 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 system 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. See https://github.com/rstudio/renv/blob/main/.github/workflows/R-CMD-check.yaml for an example of how renv uses itself for package management in its own CI tests.

## `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. This can be time consuming if your project contains a large number of files. For this reason, renv places the project library for package projects within a separate external directory by default. This directory is:

    tools::R_user_dir("renv/library", "cache")

If you want to use your own custom path, you can use, for example:

    RENV_PATHS_LIBRARY_ROOT = ~/.renv/library

If you’d prefer to keep your project library within the project directory, you can instead set:

    RENV_PATHS_LIBRARY = renv/library

within an appropriate `.Renviron` startup profile.

By default, library paths will be formed using the project name, alongside a unique identifier generated from the full project path. These paths are of the form:

    <name>-<id>

If you’d prefer to omit the `<id>`, then you can set the environment variable:

    RENV_PATHS_LIBRARY_ROOT_ASIS = TRUE

to instruct renv to forego the use of an identifier.