From bahri.gencsoy on February 15, 2013 04:57:01

FactoryModuleBuilder doesn't respect Singleton annotations of returned types. I know this is not the intended usage of FactoryModuleBuilder but due to refactorings we encountered this situtation on site. It could have failed early instead of creating new types.

Following unit test fails, instead of throwing an exception during injector creation:

public class FactoryModuleBuilderSingletonTest {

    @Singleton
    public static class ASingleton {

    }

    public static interface SingletonsFactory {
        ASingleton getSingleton();
    }

    @Test
    public void factoryModuleBuilderShouldRespectSingleton() {
        Injector injector = Guice.createInjector(new AbstractModule() {
            @Override
            protected void configure() {
                install(new FactoryModuleBuilder().build(SingletonsFactory.class));
            }
        });
        assertSame(injector.getInstance(ASingleton.class), injector.getInstance(ASingleton.class));
        assertSame(injector.getInstance(ASingleton.class), injector.getInstance(SingletonsFactory.class).getSingleton());
    }
}

Original issue: http://code.google.com/p/google-guice/issues/detail?id=742