[CMake] C/C++ dependency scanner

[Bill Hoffman]

Steven Wilson wrote:
> Hey all,
> 
> I have a large project whose source files start as files with an 
> alternate extension (.bc).   Those files are mostly generic C files that 
> have some C++ like features that are preprocessed into vanilla C files 
> using a custom C pre-processor.   My project uses an 
> add_custom_command() call to put the file through the necessary steps to 
> go from .bc to a .c file.    By the time it becomes a .c file, the C 
> preprocessor(and the custom preprocessor) has already run and all the 
> header files, etc have been put into the .c file.     I need a way to 
> generate a list of dependencies (ie header files) for the original .bc 
> file so that my add_custom_command() call can use those file names in 
> the DEPEND section so that the .c file gets regenerated correctly when 
> any of the dependencies change.
> 
> I know different techniques for getting this information into CMake once 
> the list is compiled for any give source file, but I'm not sure how to 
> generate the list.   Can CMake's C dependency scanner be invoked (using 
> cmake -E cmake_depends) to create this kind of list.   The .bc files are 
> generic C (from a preprocessor scanning point of view) so CMake's 
> dependency scanner should be able to produce this information.    If 
> cmake -E cmake_depends cannot function for this task, does anyone know 
> of another tool that could be forced into service for this type of 
> functionality?
> 
I have a hack of an idea that might work....

If you could changed your bc -> c generator to put in the #include lines 
, but with if blockers around it:

#if FOOL_CMAKE_DEPEND_SCANNER
#include "foo.h"
#include "bar.h"
#endif

Since CMake ignores #if directives will depend on foo and bar, but the c 
compiler will not expand them.

-Bill