[Rd] R package dependency issues when namespace is not attached

[Jeroen Ooms]

I have always assumed that having a package in the 'Depends' field
would automatically also import the namespace. However, it seems that
in R 2.15, dependencies do not become available until the package is
actually attached to the searchpath. Is this intended behavior?

The problem appears as follows: Suppose there is a package 'Child'
which Depends, but does not explicitly import a package called
'Parent' and contains a function that calls out to an object in the
namespace of 'Parent'. When this function is called without attaching
'Child' to the search path, the function in 'Parent' cannot be found.

Here an example from the manual of the bigdata package, but the
problem is very widespread:

x = matrix(rnorm(50*80),50,80)
beta = c(3,2,1.5,rep(0,77))
y = rnorm(50) + x%*%beta
z1 = bigdata::lasso.stars(x,y)

The example fails because lasso.stars depends on 'glmnet' which is not
loaded until bigdata is attached. The only way to be able to call
lasso.stars is to actually attach the bigdata package:

library(bigdata)
z1 = bigdata::lasso.stars(x,y)

Now to further complicate things, it seems that this problem is
inherited to any 'grandchild' package that imports, in this case, the
lasso.stars function. I have a hard time finding a good example but I
am sure they are out there.

Is this a bug? I know that it can be avoided by asking package authors
to use Imports instead of Depends, but in practice the majority of the
packages on CRAN still use Depends. It seems like the problem is
easily fixed if R would automatically import the namespace of any
Depends packages into to the child package namespace?