Thanks for the report and the examples - and they do not have to be that verbose, it is enough to just define and use a command, e.g.

cat("\\newcommand{\\mac1}{MAC1:#1}\\mac1{}", file=f)
rd <- tools::parse_Rd(f)

Whenever you get an error message like "Value of SET_STRING_ELT() must be a 'CHARSXP' not a 'NULL'", there is a bug (at least the error message should be relevant/informative).

I am testing a patch that will allow empty arguments to macros (they will expand to an empty string, like in LaTeX).

Best
Tomas

On 05/14/2018 11:23 PM, Georgi Boshnakov wrote:
Bug or feature?

I get the following error from parse_Rd() when a user Rd macro (including 
system ones) is invoked with empty argument {},
eg \mymacro{}:

Error in tools::parse_Rd(fn) :
   Value of SET_STRING_ELT() must be a 'CHARSXP' not a 'NULL'

A full example is further below with the system macro \CRANpkg{}. In this 
example it doesn't make sense to use empty argument but the error is not 
specific to this particular macro.

------
Georgi Boshnakov


Create an Rd file containing system macro \CRANpkg{bibtex}, parse_Rd() is ok:

=================
fn <- tempfile()
writeLines("\\name{dummyfun}
\\alias{dummyfun}
\\title{Dummy title}
\\description{Dummy description}
\\usage{
dummyfun(x, ...)
}
\\arguments{
   \\item{x}{a value.}
   \\item{\\dots}{further arguments.}
}
\\details{
     \\CRANpkg{bibtex}
}
", fn)

tools::parse_Rd(fn)
...
\details{
     \href{{https://CRAN.R-project.org/package=bibtex}{\pkg{bibtex}}}
}

================

With empty argument - \CRANpkg{} - Rd parser throws error. Of course it is 
silly in this example but I have used it with other user defined  macros where 
it may make sense to have empty argument.

================
writeLines("\\name{dummyfun}
\\alias{dummyfun}
\\title{Dummy title}
\\description{Dummy description}
\\usage{
dummyfun(x, ...)
}
\\arguments{
   \\item{x}{a value.}
   \\item{\\dots}{further arguments.}
}
\\details{
     \\CRANpkg{}
}
", fn)
tools::parse_Rd(fn)
Error in tools::parse_Rd(fn) :
   Value of SET_STRING_ELT() must be a 'CHARSXP' not a 'NULL'

        [[alternative HTML version deleted]]

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