Namespace Dependencies Not Required

Namespace dependencies not required

If you use import or importFrom in your NAMESPACE file, you should have an entry for that package in the Imports section of your DESCRIPTION file (unless there is a reason that you need to use Depends in which case the package should have an entry in Depends, and not Imports)

Here is a relevant section of Writing R Extensions

The ‘Imports’ field lists packages whose namespaces are imported from (as specified in the NAMESPACE file) but which do not need to be attached. Namespaces accessed by the ‘::’ and ‘:::’ operators must be listed here, or in ‘Suggests’ or ‘Enhances’ (see below). Ideally this field will include all the standard packages that are used, and it is important to include S4-using packages (as their class definitions can change and the DESCRIPTION file is used to decide which packages to re-install when this happens). Packages declared in the ‘Depends’ field should not also be in the ‘Imports’ field.

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I made a package with a single function f. I made a NAMESPACE file with the same importFrom line that you say you have in yours.

NAMESPACE file

export("f")
importFrom("ggplot2","ggplot","geom_histogram")

At this point, if I run R CMD check, as expected, I get an error:

Namespace dependency not required: ‘ggplot2’

But, if I add Imports: ggplot2 to the DESCRIPTION such that my DESCRIPTION file is as follows, it passes R CMD check with no problems.

DESCRIPTION file

Package: anRpackage
Type: Package
Title: What the package does (short line)
Version: 1.0
Date: 2012-11-07
Author: Me
Maintainer: Who to complain to <yourfault@somewhere.net>
Description: More about what it does (maybe more than one line)
License: GPL
Imports: ggplot2

Namespace dependencies not required error although I've used Imports in DESCRIPTION

When R CMD check runs, it built a binary package .zip file on the parent folder of the package's folder, and also a folder call pkgname.check. I think the next time R CMD check runs, it may not rebuild that folder or that file, depending on whether changes have been made in the package. I deleted those file and folder and rebuild, everything works.

Mysterious Namespace dependency not required: ‘rlang’

It turns out that the devtools::check() error was a ghost somewhere in a sqlpetr.Rcheck folder that it creates next door to the package directory. Once that error message had been issued it would not go away, even after I corrected the problem. Once I deleted that directory, the error message disappeared.

import NAMESPACE and DESCRIPTION question?

I would suggest reading the Namespaces chapter of Hadley's R Packages book. But in short, the answer is No.

Are imported functions in the NAMESPACE file attached to the R session when the main package is attached?

No, they are not. Imported functions are available for use in the package internals, but not attached to the user's search tree.

Another source for info is, of course, Writing R Extensions. They describe IMPORTS as:

The ‘Imports’ field lists packages whose namespaces are imported from (as specified in the NAMESPACE file) but which do not need to be attached.

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As a demonstration, the current version of ggplot2, v 3.2.1, has import(scales) in its NAMESPACE file. In a fresh R session, we can load ggplot2 and observe that the scales package is not attached:

library(ggplot2)
percent(1)
# Error in percent(1) : could not find function "percent"
scales::percent(1)
# [1] "100%"

ggplot2 uses functions from scales internally, and can do so without using the package::function notation. This is what the import(scales) accomplishes. However, unlike with Depends, scales is not attached for the user.

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