containerAllowsExternalProviders()
        def action = Mock(Action)
        def provider1 = Mock(CollectionProviderInternal)
        def provider2 = Mock(CollectionProviderInternal)

        container.addAllLater(provider1)

        when:
        container.all(action)

        then:
        1 * action.execute(c)

import org.gradle.api.Action;
import org.gradle.api.internal.DefaultMutationGuard;
import org.gradle.api.internal.MutationGuard;
import org.gradle.api.internal.provider.ChangingValue;
import org.gradle.api.internal.provider.CollectionProviderInternal;
import org.gradle.api.internal.provider.Collector;
import org.gradle.api.internal.provider.Collectors.ElementFromProvider;
import org.gradle.api.internal.provider.Collectors.ElementsFromCollectionProvider;

        public int hashCode() {
            return Objects.hashCode(provider);
        }

        @Override
        public int size() {
            if (provider instanceof CollectionProviderInternal) {
                return ((CollectionProviderInternal) provider).size();
            } else {
                throw new UnsupportedOperationException();
            }
        }

        @Override

import org.gradle.api.provider.Provider;

import java.util.Collection;

public interface CollectionPropertyInternal<T, C extends Collection<T>> extends PropertyInternal<C>, HasMultipleValues<T>, CollectionProviderInternal<T, C> {
    @Override
    Class<T> getElementType();

    /**
     * Adds an element to the property value.
     *
     * <p>