if (source is TransformedArtifactSet) {
            // Should only be contained in a ResolutionBackedFileCollection
            throw IllegalArgumentException("Found artifact set $source but was not expecting an artifact set")
        } else {
            FileCollectionStructureVisitor.VisitType.Visit
        }

            }
        }

        @Override
        public FileCollectionStructureVisitor.VisitType prepareForVisit(FileCollectionInternal.Source source) {
            if (source instanceof LocalDependencyFiles) {
                return FileCollectionStructureVisitor.VisitType.NoContents;
            }
            return FileCollectionStructureVisitor.VisitType.Visit;
        }

        @Override

     * This is final - override {@link #visitContents(FileCollectionStructureVisitor)} instead to provide the contents.
     */
    @Override
    public final void visitStructure(FileCollectionStructureVisitor visitor) {
        if (visitor.startVisit(OTHER, this)) {
            visitContents(visitor);
        }
    }

    protected void visitContents(FileCollectionStructureVisitor visitor) {
        visitor.visitCollection(OTHER, this);

                result.add(new BrokenArtifacts(failure));
            }
        });
    }

    @Override
    public FileCollectionStructureVisitor.VisitType prepareForVisit(FileCollectionInternal.Source source) {
        // Visit everything
        return FileCollectionStructureVisitor.VisitType.Visit;
    }

    public static class TransformedArtifact implements ResolvedArtifactSet.Artifacts, RunnableBuildOperation {

        then:
        difference.files == toLinkedSet(file1)
    }

    def "can visit the result of subtracting a collection"() {
        def visitor = Mock(FileCollectionStructureVisitor)
        File file1 = new File("f1")
        File file2 = new File("f2")
        File file3 = new File("f3")
        def collection1 = new TestFileCollection(file1, file2)

    }

    public abstract ImmutableAttributes getRequestAttributes();

    @Override
    public void visit(Visitor listener) {
        FileCollectionStructureVisitor.VisitType visitType = listener.prepareForVisit(this);
        if (visitType == FileCollectionStructureVisitor.VisitType.NoContents) {
            listener.visitArtifacts(new EndCollection(this));
            return;
        }

import org.gradle.api.internal.artifacts.ivyservice.TypedResolveException;
import org.gradle.api.internal.file.FileCollectionInternal;
import org.gradle.api.internal.file.FileCollectionStructureVisitor;
import org.gradle.api.internal.tasks.TaskDependencyFactory;
import org.gradle.api.internal.tasks.TaskDependencyResolveContext;
import org.gradle.internal.DisplayName;
import org.gradle.internal.UncheckedException;

import org.gradle.api.internal.CollectionCallbackActionDecorator
import org.gradle.api.internal.DefaultDomainObjectSet
import org.gradle.api.internal.file.FileCollectionInternal
import org.gradle.api.internal.file.FileCollectionStructureVisitor
import org.gradle.api.plugins.ExtensionAware
import org.gradle.language.base.LanguageSourceSet
import org.gradle.language.nativeplatform.HeaderExportingSourceSet
import org.gradle.language.rc.WindowsResourceSet

                visitor.accept(child1)
                visitor.accept(child2)
            }
        }
        def visitor = Mock(FileCollectionStructureVisitor)

        when:
        collection.visitStructure(visitor)

        then:
        1 * visitor.startVisit(FileCollectionInternal.OTHER, collection) >> true
        1 * child1.visitStructure(visitor)

package org.gradle.execution.plan;

import org.gradle.api.file.FileTreeElement;
import org.gradle.api.internal.TaskInternal;
import org.gradle.api.internal.file.FileCollectionInternal;
import org.gradle.api.internal.file.FileCollectionStructureVisitor;
import org.gradle.api.internal.file.FileTreeInternal;
import org.gradle.api.internal.file.collections.FileSystemMirroringFileTree;
import org.gradle.api.problems.Severity;