Element cleanPlugin = plugins.child("plugin").orElse(null);
            Element executions = cleanPlugin.child("executions").orElse(null);
            Element execution = executions.child("execution").orElse(null);
            Element phase = execution.child("phase").orElse(null);

            assertEquals("pre-clean", phase.textContent(), "Phase should remain as pre-clean for 4.0.0");

            </configuration>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-source-plugin</artifactId>
        <executions>
          <execution>
            <id>attach-test-sources</id>
            <phase>post-integration-test</phase>
            <goals><goal>test-jar</goal></goals>
          </execution>
        </executions>
      </plugin>
      <plugin>

import org.apache.maven.project.MavenProject;

/**
 * Lifecycle mapping delegate component interface. Calculates project build execution plan given {@link Lifecycle} and
 * lifecycle phase. Standard lifecycles use plugin execution {@code <phase>} or mojo default lifecycle phase to
 * calculate the execution plan, but custom lifecycles can use alternative mapping strategies.
 */
@Named(DefaultLifecycleMappingDelegate.HINT)
@Singleton

                <configuration/>
                <executions>
                    <execution>
                        <id>compile</id>
                        <phase>process-sources</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>test-compile</id>

        <executions>
          <execution>
            <id>default-compile</id>
            <configuration>
              <compilerArgs combine.children="append" combine.self="append">
                <arg>-XDignore.symbol.file</arg>
              </compilerArgs>
            </configuration>
          </execution>
          <execution>
            <id>compile-java9</id>

        <executions>
          <execution>
            <id>default-compile</id>
            <configuration>
              <compilerArgs combine.children="append" combine.self="append">
                <arg>-XDignore.symbol.file</arg>
              </compilerArgs>
            </configuration>
          </execution>
          <execution>
            <id>compile-java9</id>

public enum PhaseExecutionPoint {
    /**
     * Execution must occur before any executions of the phase proper. Failure of any {@code #BEFORE} dynamic phase
     * execution will prevent the {@link #AT} phase but will not prevent any {@link #AFTER} dynamic phases.
     */
    BEFORE("before:"),
    /**
     * Execution is the execution of the phase proper. Failure of any {@code #AT} dynamic phase execution will fail

        MojoDescriptor mojoDescriptor = execution.getMojoDescriptor();

        if (mojoDescriptor == null) {
            mojoDescriptor = pluginManager.getMojoDescriptor(
                    execution.getPlugin(),
                    execution.getGoal(),
                    project.getRemotePluginRepositories(),
                    session.getRepositorySession());

            execution.setMojoDescriptor(mojoDescriptor);
        }

                }

                PluginExecution execution = new PluginExecution();
                execution.setId(getExecutionId(plugin, gs.goal));
                execution.setPhase(phase);
                execution.setPriority(i - mojos.size());
                execution.getGoals().add(gs.goal);

                execution.setLocation("", location);
                execution.setLocation("id", location);

     * method is called on a new/empty execution request before the caller mutates it to fit its needs.
     *
     * @param request The execution request to populate, must not be {@code null}.
     * @param toolchains The toolchains to copy into the execution request, may be {@code null}.
     * @return The populated execution request, never {@code null}.