new_contents: #!/usr/bin/env python3
  
  import sys
  import re
  
  MAPPING = {
      'core_read.cpp': 'core_io.cpp',
      'core_write.cpp': 'core_io.cpp',
  }
  
  # Directories with header-based modules, where the assumption that .cpp files
  # define functions and variables declared in corresponding .h files is
  # incorrect.
  HEADER_MODULE_PATHS = [
      'interfaces/'
  ]
  
  def module_name(path):
      if path in MAPPING:
          path = MAPPING[path]
      if any(path.startswith(dirpath) for dirpath in HEADER_MODULE_PATHS):
          return path
      if path.endswith(".h"):
          return path[:-2]
      if path.endswith(".c"):
          return path[:-2]
      if path.endswith(".cpp"):
          return path[:-4]
      return None
  
  files = dict()
  deps = dict()
  
  RE = re.compile("^#include \"(.*)\"")
  
  # Iterate over files, and create list of modules
  for arg in sys.argv[1:]:
      module = module_name(arg)
      if module is None:
          print("Ignoring file %s (does not constitute module)\n" % arg)
      else:
          files[arg] = module
          deps[module] = set()
  
  # Iterate again, and build list of direct dependencies for each module
  # TODO: implement support for multiple include directories
  for arg in sorted(files.keys()):
      module = files[arg]
      with open(arg, 'r', encoding="utf8") as f:
          for line in f:
              match = RE.match(line)
              if match:
                  include = match.group(1)
                  included_module = module_name(include)
                  if included_module is not None and included_module in deps and included_module != module:
                      deps[module].add(included_module)
  
  # Loop to find the shortest (remaining) circular dependency
  have_cycle = False
  while True:
      shortest_cycle = None
      for module in sorted(deps.keys()):
          # Build the transitive closure of dependencies of module
          closure = dict()
          for dep in deps[module]:
              closure[dep] = []
          while True:
              old_size = len(closure)
              old_closure_keys = sorted(closure.keys())
              for src in old_closure_keys:
                  for dep in deps[src]:
                      if dep not in closure:
                          closure[dep] = closure[src] + [src]
              if len(closure) == old_size:
                  break
          # If module is in its own transitive closure, it's a circular dependency; check if it is the shortest
          if module in closure and (shortest_cycle is None or len(closure[module]) + 1 < len(shortest_cycle)):
              shortest_cycle = [module] + closure[module]
      if shortest_cycle is None:
          break
      # We have the shortest circular dependency; report it
      module = shortest_cycle[0]
      print("Circular dependency: %s" % (" -> ".join(shortest_cycle + [module])))
      # And then break the dependency to avoid repeating in other cycles
      deps[shortest_cycle[-1]] = deps[shortest_cycle[-1]] - set([module])
      have_cycle = True
  
  sys.exit(1 if have_cycle else 0)
  
subject: Introduce circular-dependencies.py