anchor.diff:            //     since if the implementation was on the command line, it must exist because of option validation
             raise_err (Errors.Fatal_MissingImplementation,
                        BU.format1 "Expected an implementation of module %s, but couldn't find one" key)
  -        | Some f -> maybe_add_suffix f
  +        | Some f -> maybe_use_cache_of f
   
   let file_of_dep = file_of_dep_aux false
   
  
positive.code:            is_implementation fn &&
             key = lowercase_module_name fn)
      in
      let maybe_add_suffix f = if use_checked_file then cache_file_name f else f in
      match d with
      | UseInterface key ->
        //This key always resolves to an interface source file
  
negative.code:       if cmd_line_has_impl key //unless the cmd line contains 'a.fst'
        && Option.isNone (Options.dep()) //and we're not just doing a dependency scan using `--dep _`
        then if Options.expose_interfaces()
             then maybe_use_cache_of (Option.get (implementation_of file_system_map key))
             else raise_err (Errors.Fatal_MissingExposeInterfacesOption,
                             BU.format3 "You may have a cyclic dependence on module %s: use --dep full to confirm. \
                                         Alternatively, invoking fstar with %s on the command line breaks \
  