[Cmake] cmUtilitySourceCommand : why relative path to source ?

[Sebastien BARRE]

Hi

Syntax:
UTILITY_SOURCE(cache_entry executable_name path_to_source [file1 file2 ...])

Is there a reason for the path_to_source to be relative to the build 
directory ? This looks odd, especially if this command is aiming at 
third-party utilities support. If these are third-party tools, they might 
be anywhere in the system, especially on a different drive.

For example, say that I'm trying to build a lib with my own VTK classes and 
I want to wrap them using the usual wrapper mechanism (provided that I know 
the path to my VTK sources, say VTK_SOURCE_DIR). This will fail :

   UTILITY_SOURCE(VTK_WRAP_TCL_EXE vtkWrapTcl ${VTK_SOURCE_DIR}/Wrapping 
vtkWrapTcl.c)

Of course, I can use something like that :

   FIND_PROGRAM(VTK_WRAP_TCL_EXE vtkWrapTcl ${VTK_BINARY_RELEASE_DIR})
but
	a) VTK_BINARY_RELEASE is something that is not very easy to get (or maybe 
I missed something), since it could be c:/[...]/build/bin/Release, or 
c:/[...]/build/bin/Debug, thus it has to be hardcoded.
	b) vtkWrapTcl.exe might not have been built, thus I also need the previous 
syntax (and I would build vtkWrapTcl myself as it's done in the 
VTK/Wrapping/ dir)

Thanks