part_of_unnamed_library

The library is unnamed. A URI is expected, not a library name '{0}', in the part-of directive.

The analyzer produces this diagnostic when a library that doesn't have a library directive (and hence has no name) contains a part directive and the part of directive in the part file uses a name to specify the library that it's a part of.

Given a part file named part_file.dart containing the following code:

part of lib;

The following code produces this diagnostic because the library including the part file doesn't have a name even though the part file uses a name to specify which library it's a part of:

part 'part_file.dart';

Change the part of directive in the part file to specify its library by URI:

part of 'test.dart';