}
            return finalizeOnNextGet || consumer == ValueSupplier.ValueConsumer.DisallowUnsafeRead;
        }

        @Override
        public ValueSupplier.ValueConsumer forUpstream(ValueSupplier.ValueConsumer consumer) {
            if (disallowUnsafeRead) {
                return ValueSupplier.ValueConsumer.DisallowUnsafeRead;
            } else {
                return consumer;
            }
        }

            interface ProjectModel {
                ConfigurableFileCollection getProp()
            }

            project.extensions.create('thing', ProjectModel.class)
            thing.prop.disallowUnsafeRead()
            thing.prop.from(layout.buildDirectory)

            try {
                thing.prop.files
            } catch(IllegalStateException e) {

        taskTypeWithOutputFileProperty()
        settingsFile << "rootProject.name = 'broken'"
        buildFile """
            task producer(type: FileProducer) {
                output.disallowUnsafeRead()
                output = layout.buildDir.file("text.out")
                def other = file('ignore')
                doFirst {
                    try {
                        output = other

        buildFile """
            interface ProjectModel {
                Property<String> getProp()
            }

            project.extensions.create('thing', ProjectModel.class)
            thing.prop.disallowUnsafeRead()
            thing.prop.set("value one")

            try {
                thing.prop.get()
            } catch(IllegalStateException e) {
                println("get failed with: " + e.message)

    }

    @Override
    public void implicitFinalizeValue() {
        state.disallowChangesAndFinalizeOnNextGet();
    }

    @Override
    public void disallowUnsafeRead() {
        state.disallowUnsafeRead();
    }

    protected abstract S finalValue(EvaluationContext.ScopeContext context, S value, ValueConsumer consumer);

    protected void setSupplier(S supplier) {

        // so we do not #disallowChanges().
        valueState.finalizeOnNextGet();
    }

    @Override
    public void disallowUnsafeRead() {
        valueState.disallowUnsafeRead();
    }

    @Override
    public int getFactoryId() {
        return ManagedFactories.ConfigurableFileCollectionManagedFactory.FACTORY_ID;
    }

    @Override

     */
    ValueProducer getProducer();

    boolean calculatePresence(ValueConsumer consumer);

    enum ValueConsumer {
        DisallowUnsafeRead, IgnoreUnsafeRead
    }

    /**
     * Carries information about the producer of a value.
     */
    interface ValueProducer {
        NoProducer NO_PRODUCER = new NoProducer();