def finalize_options(self):
        """Sets the final values for the command options.

        Defaults were set in `initialize_options`, but could have been changed
        by command-line options or by other commands.
        """
        self.ensure_dirname('source_dir')
        self.ensure_string_list('extra_proto_paths')

        if self.output_dir is None:
            self.output_dir = '.'
        self.ensure_dirname('output_dir')

        # SUBTLE: if 'source_dir' is a subdirectory of any entry in
        # 'extra_proto_paths', then in general, the shortest --proto_path prefix
        # (and the longest relative .proto filenames) must be used for
        # correctness. For example, consider:
        #
        #     source_dir = 'a/b/c'
        #     extra_proto_paths = ['a/b', 'x/y']
        #
        # In this case, we must ensure that a/b/c/d/foo.proto resolves
        # canonically as c/d/foo.proto, not just d/foo.proto. Otherwise, this
        # import:
        #
        #     import "c/d/foo.proto";
        #
        # would result in different FileDescriptor.name keys from "d/foo.proto".
        # That will cause all the definitions in the file to be flagged as
        # duplicates, with an error similar to:
        #
        #     c/d/foo.proto: "packagename.MessageName" is already defined in file "d/foo.proto"
        #
        # For paths in self.proto_files, we transform them to be relative to
        # self.proto_root_path, which may be different from self.source_dir.
        #
        # Although the order of --proto_paths is significant, shadowed filenames
        # are errors: if 'a/b/c.proto' resolves to different files under two
        # different --proto_path arguments, then the path is rejected as an
        # error. (Implementation note: this is enforced in protoc's
        # DiskSourceTree class.)

        if self.proto_root_path is None:
            self.proto_root_path = os.path.normpath(self.source_dir)
            for root_candidate in self.extra_proto_paths:
                root_candidate = os.path.normpath(root_candidate)
                if self.proto_root_path.startswith(root_candidate):
                    self.proto_root_path = root_candidate
            if self.proto_root_path != self.source_dir:
                self.announce('using computed proto_root_path: ' + self.proto_root_path, level=2)

        if not self.source_dir.startswith(self.proto_root_path):
            raise DistutilsOptionError('source_dir ' + self.source_dir +
                                       ' is not under proto_root_path ' + self.proto_root_path)

        if self.proto_files is None:
            files = glob.glob(os.path.join(self.source_dir, '*.proto'))
            if self.recurse:
                files.extend(glob.glob(os.path.join(self.source_dir, '**', '*.proto'), recursive=True))
            self.proto_files = [f.partition(self.proto_root_path + os.path.sep)[-1] for f in files]
            if not self.proto_files:
                raise DistutilsOptionError('no .proto files were found under ' + self.source_dir)

        self.ensure_string_list('proto_files')

        if self.protoc is None:
            self.protoc = os.getenv('PROTOC')
        if self.protoc is None:
            self.protoc = spawn.find_executable('protoc')
Sets the final values for the command options.

        Defaults were set in `initialize_options`, but could have been changed
        by command-line options or by other commands.
        
deps/protobuf/python/protobuf_distutils/protobuf_distutils/generate_py_protobufs.py