[cmake-developers] CMakeParseArguments: Do not skip empty arguments

[Alexander Neundorf]

On Tuesday 05 November 2013, Daniele E. Domenichelli wrote:
> Hello all,
> 
> Current implementation of cmake_parse_arguments skips empty arguments.
> 
> For example:
> 
>   cmake_parse_arguments("OPTION" "SINGLE" "MULTI" ${ARGN})
> 
> with ARGN that is set using something like:
> 
>   <args> SINGLE "" <more args>  # (<args>;SINGLE;;<more args>)
>   <args> SINGLE ""  # (<args>;SINGLE;)
> 
> it will fail in 3 different ways:
> 
> 1) because the "foreach" skips empty arguments
> 2) because list(APPEND <list> ${currentArg}) will fail to append an
>    empty element to the list if currentArg is an empty string.
> 3) because empty arguments are not passed to cmake_parse_arguments
>    if not quoted, i.e. if ARGN="a;;b"
>    * ${ARGN} will pass the arguments "a", "b"
>    * "${ARGN}" will pass the arguments "a", "", "b"

Not sure about the third point. It could be done intentionally that way in 
order to ignore empty strings.
 
> I wrote a small patch to fix this, you can find it in the
> CMakeParseArguments_EmptyArgs topic. This patch fixes the first
> behaviour using foreach(IN LISTS) version, the second by enclosing
> currentArg in quotes where required, and finally fixes the documentation
> in order to suggest to use quoted  "${ARGN}" in order not to miss the
> empty arguments at the end of the list.
> 
> I don't know if this is to be considered a change of behaviour though,
> but I'd rather consider it a bug, and I would like to see it fixed in
> the next bugfix release... what do you think?

cmake_parse_arguments() is used in quite a few places in the meantime, so I 
don't really feel good about changing its behaviour in general.
Maybe an option for the macro what it should do with empty values ?

Alex