[CMake] Call function from name and list, including empty elements?

[Jan Wielemaker]

Hi

I'm converting a big project (SWI-Prolog) to cmake. Still a newbie wrt.
cmake, but quite happy. There is one thing that I can't get done:
install the system using symbolic links to the source tree. This is in
this case really handy for developers.

I've come as far as understanding:

   - The generator creates cmake_install.cmake
   - make/ninja/... install calls cmake -P cmake_install.cmake
   - This calls file(INSTALL ....)

So, I thought I can

   - Add a file cmake_ln_install.cmake that
     - redefines file()
     - includes cmake_install.cmake

To redefine file(), I tried this to see whether this works:

function(file)
   message("Calling file(${ARGN})")
   _file(${ARGN})
endfunction()

But ... some of the file() calls contain empty strings ("") in the
argument vector.  All the rest works fine.

On stack overflow [1], the suggestion was to use "${ARGN}", which
indeed keeps the empty lists and works fine if the receiver is a
function iterating over its argument vector.  After downloading
the cmake source it turns out file() is builtin (C++) and complains
to require at least 2 arguments.  I tried passing the first two
as file(${arg1} ${arg2} "${ARGN}"), which would (I think) work for
a user function, but doesn't for a builtin.

So, my question is

   - Is there a way to redefine a builtin function that passes
     empty strings correctly to the original?
   - If not, should this be considered a bug ...

	Thanks --- Jan

P.s.	I'd also like to see the possibility to create symlinks
	in cmake, other than calling cmake -E ...

[1] https://stackoverflow.com/questions/52480737/pass-empty-strings-in-cmake