identifiers.put(ident, method);
          }
        }
      }
    }
    return ImmutableList.copyOf(identifiers.values());
  }

  /** Global cache of classes to their flattened hierarchy of supertypes. */
  private static final LoadingCache<Class<?>, ImmutableSet<Class<?>>> flattenHierarchyCache =
      CacheBuilder.newBuilder()
          .weakKeys()
          .build(

 * <p>
 * This builder applies two orthogonal transformations:
 * <ul>
 *   <li><b>Dependency Flattening</b>: When enabled via {@code maven.consumer.pom.flatten=true}, dependency management
 *       is flattened into direct dependencies for non-POM projects, and mixins are removed.</li>
 *   <li><b>Model Version Handling</b>: When {@code preserve.model.version=true} is set, the consumer POM

    /**
     * Shortcut for {@code getService(DependencyResolver.class).flatten(...)}.
     *
     * @param node node for which to get a flattened list
     * @param scope build path scope (main compile, test compile, etc.) of desired nodes
     * @return flattened list of node with the given build path scope

          <type>String</type>
          <description>pathScope used to flatten dependencies</description>
        </field>
        <field>
          <name>requestType</name>
          <required>false</required>
          <version>2.0.0+</version>
          <type>String</type>
          <description>either {@code collect}, {@code flatten}, or {@code resolve}</description>
        </field>
      </fields>
    </class>

 * <ul>
 *   <li><strong>maven-exec-plugin</strong>: Upgrades to version 3.2.0 or higher</li>
 *   <li><strong>maven-enforcer-plugin</strong>: Upgrades to version 3.0.0 or higher</li>
 *   <li><strong>flatten-maven-plugin</strong>: Upgrades to version 1.2.7 or higher</li>
 *   <li><strong>maven-shade-plugin</strong>: Upgrades to version 3.5.0 or higher</li>

            new PluginUpgrade(
                    DEFAULT_MAVEN_PLUGIN_GROUP_ID, "maven-enforcer-plugin", "3.0.0", MAVEN_4_COMPATIBILITY_REASON),
            new PluginUpgrade("org.codehaus.mojo", "flatten-maven-plugin", "1.2.7", MAVEN_4_COMPATIBILITY_REASON),
            new PluginUpgrade(
                    DEFAULT_MAVEN_PLUGIN_GROUP_ID, "maven-shade-plugin", "3.5.0", MAVEN_4_COMPATIBILITY_REASON),
            new PluginUpgrade(

                    <build>
                        <plugins>
                            <plugin>
                                <groupId>org.codehaus.mojo</groupId>
                                <artifactId>flatten-maven-plugin</artifactId>
                                <version>1.3.0</version>
                            </plugin>
                        </plugins>
                    </build>
                </project>

 *
 * @since 4.0.0
 */
@Experimental
@Immutable
public interface DependencyResolverRequest extends RepositoryAwareRequest {

    enum RequestType {
        COLLECT,
        FLATTEN,
        RESOLVE
    }

    @Nonnull
    RequestType getRequestType();

    @Nonnull
    Optional<Project> getProject();

    @Nonnull
    Optional<Artifact> getRootArtifact();

    @Nonnull