[Rd] improve 'package not installed' load errors?

[Duncan Murdoch]

On 26/10/2016 5:52 AM, Martin Maechler wrote:
>>>>>> Duncan Murdoch <murdoch.duncan at gmail.com>
>>>>>>     on Mon, 24 Oct 2016 14:54:16 -0400 writes:
>
>     > On 24/10/2016 1:51 PM, Kevin Ushey wrote:
>     >> Hi R-devel,
>     >>
>     >> One of the more common issues that new R users see, and become stumped
>     >> by, is error messages during package load of the form:
>     >>
>     >> > library(ggplot2)
>     >> Error in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()),
>     >> versionCheck = vI[[j]]) :
>     >> there is no package called 'Rcpp'
>     >> Error: package or namespace load failed for 'ggplot2'
>     >>
>     >> Typically, error messages of this form are caused simply by one or
>     >> more dependent packages (in this case, 'Rcpp') not being installed or
>     >> available on the current library paths. (A side question, which I do
>     >> not know the answer to, is how users get themselves into this state.)
>
>     > I think one way to get here is to be running with several libraries.
>     > You install ggplot2 while Rcpp is available, but in a different part of
>     > the .libPaths list, then in a later session try to use it with a
>     > different .libPaths setting.
>     >>
>     >> I believe it would be helpful for new users if the error message
>     >> reported here was a bit more direct, e.g.
>     >>
>     >> > library(ggplot2)
>     >> Error: 'ggplot2' depends on package 'Rcpp', but 'Rcpp' is not installed
>     >> consider installing 'Rcpp' with install.packages("Rcpp")
>
>     > The risk with this message is that Rcpp may really be installed, but
>     > it's just not currently on .libPaths.  Detecting that situation and
>     > reporting on it looks like it would be relatively hard:  it would mean
>     > the ggplot2 installation needs to record where it found all
>     > dependencies, and if at some later time it doesn't find one, see if that
>     > location still exists and would still work (in which case the message
>     > should suggest modifying .libPaths).  I think that's too much work.
>
>     > Even a simple change like
>
>     > Error: 'ggplot2' depends on package 'Rcpp', but 'Rcpp' was not found
>
>
>     > might not be easy (which function knows both names?)
>
>     > However, if you want to suggest a patch to implement this,
>     > I would take a look.
>
> I woul want to take a look, even before that. Our current error
> handling here should be revised, I think :

If you've got the time to do that, please do so.  My message really 
meant "I have too much on my plate right now to develop a patch, but 
this is important enough that I would evaluate one that you produced."

I think my "full plate" status is going to last until the end of the 
year; after that I may have some more free time.

Duncan Murdoch


>
> For library() the user sees *two* error messages: In my "setup"
> ((where I did fiddle with .libPaths() to provoke the error,
>   exactly as Duncan mentioned)), I have
>
>>>> library(ggplot2)
>
> 1. >> Error in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]) :
>>>   there is no package called ‘gtable’
>
> 2. >> Error: package or namespace load failed for ‘ggplot2’
>
> and together they at least give a good clue to the user (yes,
> not easy enough for the beginner, I agree).
>
> However, because the above is already a kludge (only one of the
> two error messages is part of the error that is signalled !!!),
> the situation is even worse if the user (or her code) uses require():
>
>>>> require(ggplot2)
>>> Loading required package: ggplot2
>>> Error in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]) :
>>>   there is no package called ‘gtable’
>>>>
>
> Only the 2nd of  library()'s "Error" messages is transfered to require()
> [or any other caller of library() !]
> and that is in itself very unsatisfactory.
>
>
>     >> In other words, it might be helpful to avoid printing the
>     >> 'loadNamespace()' call on error (since it's mostly just scary /
>     >> uninformative), and check up-front that the package is installed
>     >> before attempting to call 'loadNamespace()'.
>
> well, yes, one should not use try() there, but tryCatch() anyway :
> try() is a wrapper around tryCatch() and I agree the error
> message should not be printed which try() *does* by default, but
> should be *combined* with the "2nd one" to one error.. which
> then also is automatically "transfered" to require() or another caller.
>
> There is a small problem for producing a really nice error
> message : It is *wrong* to assume we can easily use  sub() or
> similar to get the dependecy package name ('gtable' or 'Rcpp' in
> the above examples) from the error message :
>
> The error message may be and often is translated {{apart from the
>  "Error in " of the first error message which is  never
>  translated, it seems, but that is different issue(buglet) }} :
>
> a) French:
>
>> Sys.setenv("LANGUAGE"="fr"); Sys.setlocale("LC_MESSAGES", "fr_FR.UTF-8")
>> library(ggplot2)
> Error in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]) :
>   aucun package nommé ‘gtable’ n'est trouvé
> Erreur : le chargement du package ou de l'espace de noms a échoué pour ‘ggplot2’
>
> b) German:
>
>> Sys.setenv("LANGUAGE"="de"); Sys.setlocale("LC_MESSAGES", "de_CH.UTF-8")
> [1] "de_CH.UTF-8"
>> library(ggplot2)
> Error in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]) :
>   es gibt kein Paket namens ‘gtable’
> Fehler: Laden von Paket oder Namensraum für ‘ggplot2’ fehlgeschlagen
>>
>
> c) Japanase :
>
>> Sys.setenv("LANGUAGE"="ja"); Sys.setlocale("LC_MESSAGES", "ja_JP.UTF-8")
> [1] "ja_JP.UTF-8"
>> library(ggplot2)
> Error in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]) :
>    ‘gtable’ という名前のパッケージはありません
>  エラー:  ‘ggplot2’ に対するパッケージもしくは名前空間のロードが失敗しました
>>
>
> We could try to look for the sQuote(.)'d package name
> independently of the translation of the error message and use
> that in the "merged" error message.
>
>
> Martin
>
>
>     >>  I'm sure a number of
>     >> novice users will still just throw their hands up in the air and say
>     >> "I don't know what to do", but I think this would help steer a number
>     >> of users in the right direction.
>     >>
>     >> (The prescription to suggest installing a package from CRAN if
>     >> available might be a step too far, but I think making it more clear
>     >> that the error is due to a missing dependent package would help.)
>     >>
>     >> Any thoughts?
>     >> Kevin
>