* is optional or mandatory), and possible exclusions for transitive dependencies.
 * The {@linkplain #getVersionConstraint() version} and the {@linkplain #getOptional() obligation}
 * may not be defined precisely.
 *
 * @since 4.0.0
 */
@Experimental
@Immutable
public interface DependencyCoordinates extends ArtifactCoordinates {
    /**

  private static final Collector<Object, ?, Optional<Object>> TO_OPTIONAL =
      Collector.of(
          ToOptionalState::new,
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *

                && Objects.equals(d1.getScope(), d2.getScope())
                && Objects.equals(d1.getSystemPath(), d2.getSystemPath())
                && Objects.equals(d1.getOptional(), d2.getOptional())
                && equals(d1.getExclusions(), d2.getExclusions());
    }

    private boolean equals(Collection<Exclusion> ce1, Collection<Exclusion> ce2) {
        if (ce1.size() == ce2.size()) {

     * The value is computed during the dependencies collection phase.
     *
     * @return {@code true} if the dependency is optional, or {@code false} if mandatory
     * @see DependencyCoordinates#getOptional()
     */
    boolean isOptional();

    /**
     * {@return coordinates with the same identifiers as this dependency}
     */
    @Nonnull
    @Override
    DependencyCoordinates toCoordinates();

            exclusions.add(convert(exclusion));
        }

        return new Dependency(
                artifact,
                dependency.getScope(),
                dependency.getOptional() != null ? dependency.isOptional() : null,
                exclusions);
    }

    private Exclusion convert(org.apache.maven.model.Exclusion exclusion) {

                String scope = dependency.getScope() != null ? dependency.getScope() : "";
                return session.requireDependencyScope(scope);
            }

            @Override
            public Boolean getOptional() {
                return dependency.isOptional();
            }

            @Nonnull
            @Override
            public Collection<Exclusion> getExclusions() {

                .collect(Collectors.toList());

        return new Dependency(
                artifact,
                dependency.getScope(),
                dependency.getOptional() != null ? dependency.isOptional() : null,
                exclusions);
    }

    private static Exclusion toExclusion(org.apache.maven.model.Exclusion exclusion) {

            if (request.getValidationLevel() >= ModelBuildingRequest.VALIDATION_LEVEL_MAVEN_2_0) {
                validateBoolean(
                        prefix, "optional", problems, errOn30, Version.V20, d.getOptional(), d.getManagementKey(), d);

                if (!management) {
                    validateVersion(

    public boolean isOptional() {
        return (getOptional() != null) ? Boolean.parseBoolean(getOptional()) : false;
    }

            ]]>
          </code>
        </codeSegment>
        <codeSegment>
          <version>4.0.0/4.0.99</version>
          <code>
            <![CDATA[
    public void setOptional(boolean optional) {
        setOptional(String.valueOf(optional));
    }

abstract class BuildTimestampValueSource : ValueSource<String, BuildTimestampValueSource.Parameters>, Describable {

    interface Parameters : ValueSourceParameters {

        @get:Optional
        val buildTimestampFromBuildReceipt: Property<String>

        @get:Optional
        val buildTimestampFromGradleProperty: Property<String>

        val runningOnCi: Property<Boolean>

        val runningInstallTask: Property<Boolean>