Problem understanding behaviour of versionCheck for loadNamespace (and when versions for Imports packages are checked)

Hi

 

I'm still exploring the R programming universe, so if this is being 
asked in the wrong place, or in the wrong way (e.g. too verbose or 
lacking in crucial detail or in the wrong format) please let me know

 

I am trying to understand when the version constraints for packages 
which appear in the Imports field of a DESCRIPTION file are checked.

 

Along the way I've hit a snag understanding what loadNamespace with 
the versionCheck argument set does.  The core of my query is 'am I 
doing something wrong, or have I stumbled across a bug?'.  Probably 
the former, but after several days I still can't figure it out, so any 
guidance, hints or outright help would be much appreciated.

 

Thanks in advance

 

Geoff

 

What I've tried so far.

 

"Writing R extensions" section 1.1.3 says

 

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

shortened for brevity ... Packages declared in the 'Depends' field 
should not also be in the 'Imports' field. Version requirements can be 
specified and are checked when the namespace is loaded (since R >= 3.0.0).

 

It is slightly ambiguous, but seems to mean that the version 
dependencies for both Depends packages and Imports packages are 
checked when the package
(namespace?) is loaded.

 

The release notes for R3.0.0 are more direct.  They say

 

"loadNamespace() allows a version specification to be given, and this 
is used to check version specifications given in the Imports field 
when a namespace is loaded"

 

But some toy (locally built and loaded) examples seem to show that 
while the Depends versions are checked, the Imports version 
constraints are not (on Windows 64, running R3.1.2, see full session_info

 

My tests (package2 imports package1) use implicit loading (via the
package1::fun1() idiom) so I have worked back to try get a minimal 
example of what's causing me problems. I have tried

 

loadNamespace('package2', versionCheck = list (op = ">=", version =
package_version('3.0')))

 

This should fail (package2 has version 0.3, not 3.0) but instead it 
seems to load package2, version 0.3 OK.

 

Reading the code of loadNamespace, there is some code which says

 

if (length(z <- versionCheck) == 3L && !do.call(z$op,

    list(as.numeric_version(version), z$version)))

    stop(gettextf("namespace %s %s is being loaded, but %s %s is 
required",

      sQuote(package), version, z$op, z$version),

       domain = NA)

 

I think it is the length(z <- versionCheck) == 3L part of the if test 
that is allowing the incorrect version be loaded.

 

The documentation for loadNamespace says that "versionCheck" is

"NULL or a version specification (a list with components op and

 

If I add a third (nonsense) component to the versionCheck argument 
list, then loadNamespace does what I expect.  Is there supposed to be 
a third component in the list, and if so what should it be? Or is this a

 

I've got this far and am now stumped, hence my query.

 

Some output from my tests.

 

d> devtools::session_info()

Session
info------------------------------------------------------------------
--

  setting  value                       

version  R version 3.1.2 (2014-10-31)

system   x86_64, mingw32             

ui       RStudio (0.98.953)          

language (EN)                        

collate  English_Australia.1252      

tz       Australia/Sydney            

 

Packages--------------------------------------------------------------
------
----

  package    * version date       source        

devtools     1.6.1   2014-10-07 CRAN (R 3.1.2)

rstudioapi   0.1     2014-03-27 CRAN (R 3.1.1)

 

d> # I think this should fail but it does not

d> loadNamespace('package2', versionCheck = list(op='>=', version =
package_version('3.0')))

<environment: namespace:package2>

  

  

  d> devtools::session_info()

Session
info------------------------------------------------------------------
--

  setting  value                       

version  R version 3.1.2 (2014-10-31)

system   x86_64, mingw32             

ui       RStudio (0.98.953)          

language (EN)                        

collate  English_Australia.1252      

tz       Australia/Sydney            

 

Packages--------------------------------------------------------------
------
----

  package    * version date       source        

devtools     1.6.1   2014-10-07 CRAN (R 3.1.2)

package2     0.3     2014-11-24 local         

rstudioapi   0.1     2014-03-27 CRAN (R 3.1.1)

 

d> #Try again with a third (nonsense) entry in the versionCheck list

d> unloadNamespace('package2')

d> loadNamespace('package2', versionCheck = list(op='>=', version =
package_version('3.0'), please = 'check it'))

Error in loadNamespace("package2", versionCheck = list(op = ">=", 
version = package_version("3.0"),  :

 namespace 'package2' 0.3 is being loaded, but >= 3.0 is required

 

 

 

d> devtools::session_info()

Session
info------------------------------------------------------------------
--

setting  value                       

version  R version 3.1.2 (2014-10-31)

system   x86_64, mingw32             

ui       RStudio (0.98.953)          

language (EN)                        

collate  English_Australia.1252      

tz       Australia/Sydney            

 

Packages--------------------------------------------------------------
------
----

package    * version date       source        

devtools     1.6.1   2014-10-07 CRAN (R 3.1.2)

rstudioapi   0.1     2014-03-27 CRAN (R 3.1.1)

d> loadNamespace('package2', versionCheck = list(op='>=', version =
package_version('0.3'), please = 'check it'))

<environment: namespace:package2>

d>


	[[alternative HTML version deleted]]