assertTrue(bean instanceof ExtensionAware);
        ExtensionAware extensionBean = (ExtensionAware) bean;

        assertThat(extensionBean.getExtensions(), notNullValue());

        Bean extn = extensionBean.getExtensions().create("nested", Bean.class);

        DynamicObjectAware dynamicBean = (DynamicObjectAware) bean;
        assertSame(dynamicBean.getAsDynamicObject().getProperty("nested"), extn);

        registerInstanceOn(modelRegistry, "projectIdentifier", PROJECT_IDENTIFIER_MODEL_TYPE, this);
        registerInstanceOn(modelRegistry, "extensionContainer", EXTENSION_CONTAINER_MODEL_TYPE, getExtensions());
        modelRegistry.getRoot().applyToSelf(BasicServicesRules.class);
    }

    private <T> void registerInstanceOn(ModelRegistry modelRegistry, String path, ModelType<T> type, T instance) {

    }

    public List<Extension> getBuildExtensions() {
        Build build = getBuild();
        if ((build == null) || (build.getExtensions() == null)) {
            return Collections.emptyList();
        } else {
            return Collections.unmodifiableList(build.getExtensions());
        }
    }

    public void addProjectReference(MavenProject project) {
        projectReferences.put(

            // extensionArtifacts
            Set<Artifact> extensionArtifacts = new HashSet<>();
            List<Extension> extensions =
                    project.getModel().getDelegate().getBuild().getExtensions();
            if (extensions != null) {
                for (Extension ext : extensions) {
                    String version;
                    if (ext.getVersion() == null || ext.getVersion().isEmpty()) {

[[task_convention]]
==== Calling `Task.getConvention()`, `Task.getExtensions()` from a task action

Calling link:{javadocPath}/org/gradle/api/Task.html#getConvention--[Task.getConvention()], link:{javadocPath}/org/gradle/api/Task.html#getExtensions--[Task.getExtensions()] from a task action at execution time is now deprecated and will be made an error in Gradle 9.0.

     *
     * @return The <code>Convention</code>. Never returns null.
     * @deprecated The concept of conventions is deprecated. Use extensions if possible.
     * @see ExtensionAware#getExtensions()
     */
    @Deprecated
    org.gradle.api.plugins.Convention getConvention();

    /**
     * <p>Compares the nesting level of this project with another project of the multi-project hierarchy.</p>

                            EMPTY,
                            problems,
                            errOn30,
                            Version.V20,
                            p.getExtensions(),
                            p.getKey(),
                            p);

                    validate20EffectivePluginDependencies(problems, p, request);
                }

                            EMPTY,
                            problems,
                            errOn30,
                            Version.V20,
                            p.getExtensions(),
                            p.getKey(),
                            p);

                    validate20EffectivePluginDependencies(problems, p, request);
                }

        CoreExtensionsStaxReader parser = new CoreExtensionsStaxReader();

        try (InputStream is = Files.newInputStream(extensionsFile.toPath())) {
            return parser.read(is, true).getExtensions();
        }
    }

    private ClassRealm setupContainerRealm(
            ClassWorld classWorld, ClassRealm coreRealm, List<File> extClassPath, List<CoreExtensionEntry> extensions)

For example, here's how you configure the groovy sources from a plugin:

```java
GroovySourceDirectorySet groovySources = sourceSet.getExtensions().getByType(GroovySourceDirectorySet.class);
groovySources.setSrcDirs(Arrays.asList("sources/groovy"));
```

[[old_artifact_transforms_api]]
==== Registering artifact transforms extending `ArtifactTransform`