# Package sources

    library(renv)

# Package sources

renv uses an installed package’s `DESCRIPTION` file to infer its source. For example, packages installed from the CRAN repositories typically have the field:

    Repository: CRAN

set, and renv takes this as a signal that the package was retrieved from CRAN.

## Inferring package sources

The following fields are checked, in order, when inferring a package’s source:

1. The `RemoteType` field; typically written for packages installed by the devtools, remotes and pak packages,

2. The `Repository` field; for example, packages retrieved from CRAN will typically have the `Repository: CRAN` field,

3. The `biocViews` field; typically present for packages installed from the Bioconductor repositories,

As a fallback, if renv is unable to determine a package’s source from the `DESCRIPTION` file directly, but a package of the same name is available in the active R repositories (as specified in `getOption("repos")`), then the package will be treated as though it was installed from an R package repository.

If all of the above methods fail, renv will finally check for a package available from the cellar. The package cellar is typically used as an escape hatch, for packages which do not have a well-defined remote source, or for packages which might not be remotely accessible from your machine.

## Unknown sources

If renv is unable to infer a package’s source, it will inform you during `renv::snapshot()` – for example, if we attempted to snapshot a package called `skeleton` with no known source:

    > renv::snapshot()
    The following package(s) were installed from an unknown source:

            skeleton

    renv may be unable to restore these packages in the future.
    Consider reinstalling these packages from a known source (e.g. CRAN).

    Do you want to proceed? [y/N]:

While you can still create a lockfile with such packages, `restore()` will likely fail unless you can ensure this package is installed through some other mechanism.

## Custom R package repositories

Custom and local R package repositories are supported as well. The only requirement is that these repositories are set as part of the `repos` R option, and that these repositories are named. For example, you might use:

    repos <- c(CRAN = "https://cloud.r-project.org", WORK = "https://work.example.org")
    options(repos = repos)

to tell renv to work with both the official CRAN package repository, as well as a package repository you have hosted and set up in your work environment.

## Bioconductor

renv has been designed to work together as seamlessly as possible with the Bioconductor project. This vignette outlines some of the extra steps that may be required when using renv with packages obtained from Bioconductor.

## Initializing a project

To initialize renv in a project using Bioconductor, you can pass the `bioconductor` argument to `renv::init()`:

    # use the latest-available Bioconductor release
    renv::init(bioconductor = TRUE)

    # use a specific version of Bioconductor
    renv::init(bioconductor = "3.14")

This will tell renv to activate the appropriate Bioconductor repositories, and to use those repositories when attempting to restore packages.

### Bioconductor releases

Bioconductor prepares different versions of its package repositories, for use with different versions of R. The version of Bioconductor used within a particular renv project is stored both as a project setting, and also within the project lockfile. This allows you to “lock” a particular project to a particular Bioconductor release, even as new Bioconductor releases are made available for newer versions of R.

To set the version of Bioconductor used in a project, you can use:

    renv::settings$bioconductor.version("3.14")

If you later choose to upgrade R, you may need to upgrade the version of Bioconductor used as well.

If you want to override the Bioconductor repositories used by renv, you can also explicitly set the following option:

    options(renv.bioconductor.repos = c(...))

## The package cellar

In some cases, your project may depend on R packages which are not available from any external source, or that external source may not be accessible from the machine calling `renv::restore()`. To help accommodate these scenarios, renv allows you to prepare a package “cellar”, to be used as an ad-hoc repository of packages during restore. This allows you to provide package tarballs that can be used to restore packages which cannot be retrieved from any other source.

The environment variable `RENV_PATHS_CELLAR` can be used to customize the package cellar location. It should point to a directory containing package binaries and sources, with a structure of the form:

- `${RENV_PATHS_CELLAR}/<package>_<version>.tar.gz`; or
- `${RENV_PATHS_CELLAR}/<package>/<package>_<version>.tar.gz`

Alternatively, you can also use a project-local cellar by placing your packages within a folder located at `<project>/renv/cellar`. Note that this folder does not exist by default; you must create it to opt-in.

- `<project>/renv/cellar/<package>_<version>.tar.gz`; or
- `<project>/renv/cellar/<package>/<package>_<version>.tar.gz`

As an example, if your project depended on a package `skeleton 1.0.0`, you could place a tarball for this package in one of the following locations:

- `${RENV_PATHS_CELLAR}/skeleton_1.0.0.tar.gz`
- `${RENV_PATHS_CELLAR}/skeleton/skeleton_1.0.0.tar.gz`
- `<project>/renv/cellar/skeleton_1.0.0.tar.gz`; or
- `<project>/renv/cellar/skeleton/skeleton_1.0.0.tar.gz`

Once this is done, renv will consult these directories during future attempts to restore your packages.

You can install a package from the cellar like any other package, i.e. `renv::install("skeleton")`.

During restore, if a compatible package is located within the cellar, that copy of the package will be preferred even if that package might otherwise be accessible from its associated remote source. For example, if `skeleton 1.0.0` was also available on CRAN, `renv::restore()` would still use the tarball available in the cellar rather than the version available from CRAN.

If you want to see what paths renv is using for the cellar, you can use:

    renv:::renv_paths_cellar()

See `?paths` for more details.

### Explicit sources

You can also provide explicit source paths in the lockfile if desired. This is most useful if you are building an renv lockfile “by hand”, or need to tweak an existing lockfile to point at a separate package for installation. For example, you could have a package record in `renv.lock` of the form:

    {
      "Package": "skeleton",
      "Version": "1.0.1",
      "Source": "/mnt/r/pkg/skeleton_1.0.1.tar.gz"
    }

Packages should have the following extensions, depending on whether the archive contains a binary copy of the package or the package sources:

Platform | Binary | Sources
--- | --- | ---
Windows | `.zip` | `.tar.gz`
macOS | `.tgz` | `.tar.gz`
Linux | `.tar.gz` | `.tar.gz`

Note that on Linux, both binaries and sources should have the `.tar.gz` extension, but R and renv will handle this as appropriate during installation.

## ABI compatibility

ABI compatibility issues can arise if different packages were built against different versions of a shared dependency. For example, one package may have been built against Rcpp 1.0.6, and another package might have been built against Rcpp 1.0.7. However, because only one version of the Rcpp package can be loaded at a time within an R session, mixing of these two packages might cause issues either on load or at runtime depending on the version of Rcpp available.

It’s worth emphasizing that this is not Rcpp’s fault; a package built against Rcpp 1.0.7 would reasonably expect newer APIs made available by that version of the package would be available at runtime, and that contract would be violated if an older version of Rcpp were installed in the project library. The challenge for renv is that this build-time dependency is not clearly communicated to renv; in general, it is not possible to know what packages (and their versions) a particular package was built against.

## Build-time dependencies

R packages might occasionally (and unintentionally) take a build-time dependency on another R package – for example, a package with the code:

    # please don't do this!
    `%>%` <- magrittr::`%>%`

would take the version of `%>%` that was available from the version of magrittr that was available at build time, not the one available at run time. This could be problematic if, for example, an update to the magrittr package changed in a way that made old definitions of `%>%` incompatible with newer internal functions.

In general, it is a mistake for packages to take a build-time dependency on exported objects from another package; rather, such objects should be imported at runtime (using e.g. `importFrom()` in the package `NAMESPACE` file).