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

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

        def property = propertyWithNoValue()

        property.set(b)
        property.disallowUnsafeRead()

        b.set(c)
        b.attachOwner(owner(), displayName("<b>"))

        c.set(someValue())
        c.attachOwner(owner(), displayName("<c>"))
        c.disallowUnsafeRead()

        given:
        property."$method"()

        when:
        b.set(someOtherValue())

    }

    @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) {

        where:
        description            | propertyConfig
        "default behaviour"    | ""
        "finalize on read"     | "it.finalizeValueOnRead()"
        "disallow unsafe read" | "it.disallowUnsafeRead()"
    }

    def "task input collection property can consume the mapped output of another task"() {
        taskTypeWithInputFileProperty()
        taskTypeWithInputListProperty()

    }

    def "cannot query files when unsafe reads disallowed and host is not ready"() {
        given:
        def file = new File('one')
        collection.from('a')
        collection.disallowUnsafeRead()

        when:
        collection.files

        then:
        def e = thrown(IllegalStateException)
        e.message == "Cannot query the value of <display> because <reason>."

        // 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();

        def a = property()
        def b = property()
        def c = elementProperty()
        def property = property()
        property.disallowUnsafeRead()

        property.addAll(a)

        a.addAll(b)
        a.attachOwner(owner(), displayName("<a>"))

        b.attachOwner(owner(), displayName("<b>"))

        property.add(c)

        def a = property()
        def b = property()
        def c = valueProperty()
        def property = property()
        property.disallowUnsafeRead()

        property.putAll(a)

        a.putAll(b)
        a.attachOwner(owner(), displayName("<a>"))

        b.attachOwner(owner(), displayName("<b>"))

        property.put("c", c)