/preprocess[:file Creates a single, aggregated project file by inlining all the files that would be imported during a build, ...

/preprocess[:file] 
                     Creates a single, aggregated project file by
                     inlining all the files that would be imported during a
                     build, with their boundaries marked. This can be
                     useful for figuring out what files are being imported
                     and from where, and what they will contribute to
                     the build. By default the output is written to
                     the console window. If the path to an output file 
                     is provided that will be used instead.
                     (Short form: /pp)
                     Example:
                       /pp:out.txt