code: def generate(env):
     
     doxyfile_scanner = env.Scanner(
        DoxySourceScan,
        "DoxySourceScan",
        scan_check = DoxySourceScanCheck,
     )
  
     import SCons.Builder
     doxyfile_builder = SCons.Builder.Builder(
        action = "cd ${SOURCE.dir}  &&  ${DOXYGEN} ${SOURCE.file}",
        emitter = DoxyEmitter,
        target_factory = env.fs.Entry,
        single_source = True,
        source_scanner =  doxyfile_scanner,
     )
  
     env.Append(BUILDERS = {
        'Doxygen': doxyfile_builder,
     })
  
     env.AppendUnique(
        DOXYGEN = 'doxygen',
     )
docs: Add builders and construction variables for the
     Doxygen tool.  This is currently for Doxygen 1.4.6.