object_usage_linter not working for S4 code?

[fabian-s]

Thanks for the great package, it's a nice help with grading programming assignments in addition to its general usefulness.

However, if I try to run the default linters on S4 code (here I just use some examples from the methods-package to make this reproducible) I get:

tmpfile <- tempfile(fileext = ".R")
writeLines(example(setClass, give.lines=TRUE), con=tmpfile)
lintr::lint(tmpfile)
## Error in typeof(fun) : object 'fun' not found
## Error in body(fun) : object 'fun' not found
writeLines(example(Methods, give.lines=TRUE), con=tmpfile)
lintr::lint(tmpfile)
## Error in typeof(fun) : object 'fun' not found
## Error in body(fun) : object 'fun' not found
traceback()
## 12: body(fun)
## 11: findLocalsList(c(list(body), dropMissings(formals)))
## 10: codetools::findFuncLocals(formals(fun), body(fun))
## 9: FUN(19L[[1L]], ...)
## 8: lapply(ids_with_token(source_file, rex(start, "FUNCTION"), fun = re_matches), 
##       function(loc) {
##           id <- source_file$parsed_content$id[loc]
##         [...]
## 7: linters[[linter]](expr)
## [...]
lintr::lint(tmpfile, 
     linters=default_linters[names(default_linters) != "object_usage_linter"])
## works as expected

sessionInfo():

R version 3.1.2 (2014-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8       
 [4] LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                  LC_ADDRESS=C              
[10] LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] lintr_0.2.0

loaded via a namespace (and not attached):
 [1] codetools_0.2-8  crayon_1.1.0     digest_0.6.4     htmltools_0.2.6  igraph_0.7.1    
 [6] lazyeval_0.1.9   magrittr_1.5     packrat_0.4.1-1  parallel_3.1.2   rex_0.2.0       
[11] rmarkdown_0.3.3  stringdist_0.8.1 tools_3.1.2      yaml_2.1.13     

[jimhester]

1ba3810 should close this.

There were actually two separate issues going on here.

1. S4 classes need the methods package to be loaded and the default environment the expressions were evaulated in was baseenv(), which does not load methods.
2. If there was a error in evaluating no expression would be assigned to fun, so it would break when later body(fun) was run.

So the fix was to use globalenv() rather than baseenv() and to only continue the object usage checks if the evaluation did not error.

[jimhester]

Also using this package for homework grading is something I had never thought of, great idea!

[fabian-s]

Awesome, thank you!