Replacement version of system.fileSource:
character vectors, specifying subdirectory and file(s) within some package. The default, none, returns the root of the package. Wildcards are not supported.
a character string with the name of a single package. An error occurs if more than one package name is given.
a character vector with path names of R libraries. See ‘Details’ for the meaning of the default value of
TRUE, an error is given if there are no matching files.
system.file is called from the R console (the global
environment), this function detects if the target package was loaded with
load_all(), and if so, it uses a customized method of searching
for the file. This is necessary because the directory structure of a source
package is different from the directory structure of an installed package.
When a package is loaded with
load_all, this function is also inserted
into the package's imports environment, so that calls to
from within the package namespace will use this modified version. If this
function were not inserted into the imports environment, then the package
would end up calling