clean install

web/core/modules/workflows/src/Annotation/WorkflowType.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace Drupal\workflows\Annotation;
+
+use Drupal\Component\Annotation\Plugin;
+
+/**
+ * Defines a Workflow type annotation object.
+ *
+ * Plugin Namespace: Plugin\WorkflowType
+ *
+ * For a working example, see \Drupal\content_moderation\Plugin\Workflow\ContentModerate
+ *
+ * @see \Drupal\workflows\WorkflowTypeInterface
+ * @see \Drupal\workflows\WorkflowTypeManager
+ * @see workflow_type_info_alter()
+ * @see plugin_api
+ *
+ * @Annotation
+ */
+class WorkflowType extends Plugin {
+
+  /**
+   * The plugin ID.
+   *
+   * @var string
+   */
+  public $id;
+
+  /**
+   * The label of the workflow.
+   *
+   * @var \Drupal\Core\Annotation\Translation
+   *
+   * @ingroup plugin_translatable
+   */
+  public $label = '';
+
+  /**
+   * States required to exist.
+   *
+   * Normally supplied by WorkflowType::defaultConfiguration().
+   *
+   * @var array
+   */
+  public $required_states = [];
+
+  /**
+   * A list of optional form classes implementing PluginFormInterface.
+   *
+   * Forms which will be used for the workflow UI are:
+   * - 'configure' (\Drupal\workflows\WorkflowTypeInterface::PLUGIN_FORM_KEY)
+   * - 'state' (\Drupal\workflows\StateInterface::PLUGIN_FORM_KEY)
+   * - 'transition' (\Drupal\workflows\TransitionInterface::PLUGIN_FORM_KEY)
+   *
+   * @see \Drupal\Core\Plugin\PluginWithFormsInterface
+   * @see \Drupal\Core\Plugin\PluginFormInterface
+   * @see \Drupal\workflows\Plugin\WorkflowTypeConfigureFormBase
+   * @see \Drupal\workflows\Plugin\WorkflowTypeStateFormBase
+   * @see \Drupal\workflows\Plugin\WorkflowTypeTransitionFormBase
+   * @see \Drupal\workflows\WorkflowTypeInterface::PLUGIN_FORM_KEY
+   * @see \Drupal\workflows\StateInterface::PLUGIN_FORM_KEY
+   * @see \Drupal\workflows\TransitionInterface::PLUGIN_FORM_KEY
+   *
+   * @var array
+   */
+  public $forms = [];
+
+}

web/core/modules/workflows/src/Attribute/WorkflowType.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace Drupal\workflows\Attribute;
+
+use Drupal\Component\Plugin\Attribute\Plugin;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Defines a Workflow type attribute object.
+ *
+ * Plugin Namespace: Plugin\WorkflowType
+ *
+ * For a working example, see \Drupal\content_moderation\Plugin\Workflow\ContentModerate
+ *
+ * @see \Drupal\workflows\WorkflowTypeInterface
+ * @see \Drupal\workflows\WorkflowTypeManager
+ * @see workflow_type_info_alter()
+ * @see plugin_api
+ */
+#[\Attribute(\Attribute::TARGET_CLASS)]
+class WorkflowType extends Plugin {
+
+  /**
+   * States required to exist.
+   *
+   * Normally supplied by WorkflowType::defaultConfiguration().
+   */
+  public array $required_states = [];
+
+  /**
+   * A list of optional form classes implementing PluginFormInterface.
+   *
+   * Forms which will be used for the workflow UI are:
+   * - 'configure' (\Drupal\workflows\WorkflowTypeInterface::PLUGIN_FORM_KEY)
+   * - 'state' (\Drupal\workflows\StateInterface::PLUGIN_FORM_KEY)
+   * - 'transition' (\Drupal\workflows\TransitionInterface::PLUGIN_FORM_KEY)
+   *
+   * @see \Drupal\Core\Plugin\PluginWithFormsInterface
+   * @see \Drupal\Core\Plugin\PluginFormInterface
+   * @see \Drupal\workflows\Plugin\WorkflowTypeConfigureFormBase
+   * @see \Drupal\workflows\Plugin\WorkflowTypeStateFormBase
+   * @see \Drupal\workflows\Plugin\WorkflowTypeTransitionFormBase
+   * @see \Drupal\workflows\WorkflowTypeInterface::PLUGIN_FORM_KEY
+   * @see \Drupal\workflows\StateInterface::PLUGIN_FORM_KEY
+   * @see \Drupal\workflows\TransitionInterface::PLUGIN_FORM_KEY
+   */
+  public array $forms = [];
+
+  /**
+   * Constructs an Action attribute.
+   *
+   * @param string $id
+   *   The plugin ID.
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup|null $label
+   *   The label of the action.
+   * @param string[] $forms
+   *   A list of optional form classes implementing PluginFormInterface.
+   * @param string[] $required_states
+   *   States required to exist.
+   */
+  public function __construct(
+    public readonly string $id,
+    public readonly ?TranslatableMarkup $label = NULL,
+    array $forms = [],
+    array $required_states = [],
+  ) {
+    $this->forms = $forms;
+    $this->required_states = $required_states;
+  }
+
+}

web/core/modules/workflows/src/Entity/Workflow.php

@@ -0,0 +1,179 @@
+<?php
+
+namespace Drupal\workflows\Entity;
+
+use Drupal\Core\Config\Entity\ConfigEntityBase;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\EntityWithPluginCollectionInterface;
+use Drupal\Core\Plugin\DefaultSingleLazyPluginCollection;
+use Drupal\workflows\Exception\RequiredStateMissingException;
+use Drupal\workflows\WorkflowInterface;
+
+/**
+ * Defines the workflow entity.
+ *
+ * @ConfigEntityType(
+ *   id = "workflow",
+ *   label = @Translation("Workflow"),
+ *   label_collection = @Translation("Workflows"),
+ *   label_singular = @Translation("workflow"),
+ *   label_plural = @Translation("workflows"),
+ *   label_count = @PluralTranslation(
+ *     singular = "@count workflow",
+ *     plural = "@count workflows",
+ *   ),
+ *   handlers = {
+ *     "access" = "Drupal\workflows\WorkflowAccessControlHandler",
+ *     "list_builder" = "Drupal\workflows\WorkflowListBuilder",
+ *     "form" = {
+ *       "add" = "Drupal\workflows\Form\WorkflowAddForm",
+ *       "edit" = "Drupal\workflows\Form\WorkflowEditForm",
+ *       "delete" = "Drupal\workflows\Form\WorkflowDeleteForm",
+ *       "add-state" = "Drupal\workflows\Form\WorkflowStateAddForm",
+ *       "edit-state" = "Drupal\workflows\Form\WorkflowStateEditForm",
+ *       "delete-state" = "Drupal\workflows\Form\WorkflowStateDeleteForm",
+ *       "add-transition" = "Drupal\workflows\Form\WorkflowTransitionAddForm",
+ *       "edit-transition" = "Drupal\workflows\Form\WorkflowTransitionEditForm",
+ *       "delete-transition" = "Drupal\workflows\Form\WorkflowTransitionDeleteForm",
+ *     },
+ *     "route_provider" = {
+ *       "html" = "Drupal\Core\Entity\Routing\AdminHtmlRouteProvider",
+ *     },
+ *   },
+ *   config_prefix = "workflow",
+ *   admin_permission = "administer workflows",
+ *   entity_keys = {
+ *     "id" = "id",
+ *     "label" = "label",
+ *     "uuid" = "uuid",
+ *   },
+ *   links = {
+ *     "add-form" = "/admin/config/workflow/workflows/add",
+ *     "edit-form" = "/admin/config/workflow/workflows/manage/{workflow}",
+ *     "delete-form" = "/admin/config/workflow/workflows/manage/{workflow}/delete",
+ *     "add-state-form" = "/admin/config/workflow/workflows/manage/{workflow}/add_state",
+ *     "add-transition-form" = "/admin/config/workflow/workflows/manage/{workflow}/add_transition",
+ *     "collection" = "/admin/config/workflow/workflows",
+ *   },
+ *   config_export = {
+ *     "id",
+ *     "label",
+ *     "type",
+ *     "type_settings",
+ *   },
+ * )
+ */
+class Workflow extends ConfigEntityBase implements WorkflowInterface, EntityWithPluginCollectionInterface {
+
+  /**
+   * The Workflow ID.
+   *
+   * @var string
+   */
+  protected $id;
+
+  /**
+   * The workflow label.
+   *
+   * @var string
+   */
+  protected $label;
+
+  /**
+   * The workflow type plugin ID.
+   *
+   * @see \Drupal\workflows\WorkflowTypeManager
+   *
+   * @var string
+   */
+  protected $type;
+
+  /**
+   * The configuration for the workflow type plugin.
+   *
+   * @var array
+   */
+  protected $type_settings = [];
+
+  /**
+   * The workflow type plugin collection.
+   *
+   * @var \Drupal\Component\Plugin\LazyPluginCollection
+   */
+  protected $pluginCollection;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function preSave(EntityStorageInterface $storage) {
+    $workflow_type = $this->getTypePlugin();
+    $missing_states = array_diff($workflow_type->getRequiredStates(), array_keys($this->getTypePlugin()->getStates()));
+    if (!empty($missing_states)) {
+      throw new RequiredStateMissingException(sprintf("Workflow type '{$workflow_type->label()}' requires states with the ID '%s' in workflow '{$this->id()}'", implode("', '", $missing_states)));
+    }
+    parent::preSave($storage);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTypePlugin() {
+    return $this->getPluginCollection()->get($this->type);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPluginCollections() {
+    return ['type_settings' => $this->getPluginCollection()];
+  }
+
+  /**
+   * Encapsulates the creation of the workflow's plugin collection.
+   *
+   * @return \Drupal\Core\Plugin\DefaultSingleLazyPluginCollection
+   *   The workflow's plugin collection.
+   */
+  protected function getPluginCollection() {
+    if (!$this->pluginCollection && $this->type) {
+      $this->pluginCollection = new DefaultSingleLazyPluginCollection(\Drupal::service('plugin.manager.workflows.type'), $this->type, $this->type_settings);
+    }
+    return $this->pluginCollection;
+  }
+
+  /**
+   * Loads all workflows of the provided type.
+   *
+   * @param string $type
+   *   The workflow type to load all workflows for.
+   *
+   * @return static[]
+   *   An array of workflow objects of the provided workflow type, indexed by
+   *   their IDs.
+   *
+   *  @see \Drupal\workflows\Annotation\WorkflowType
+   */
+  public static function loadMultipleByType($type) {
+    return self::loadMultiple(\Drupal::entityQuery('workflow')->condition('type', $type)->execute());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function status() {
+    // In order for a workflow to be usable it must have at least one state.
+    return !empty($this->status) && !empty($this->getTypePlugin()->getStates());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onDependencyRemoval(array $dependencies) {
+    // Give the parent method and the workflow type plugin a chance to react
+    // to removed dependencies and report if either of these two made a change.
+    $parent_changed_entity = parent::onDependencyRemoval($dependencies);
+    $plugin_changed_entity = $this->getTypePlugin()->onDependencyRemoval($dependencies);
+    return $plugin_changed_entity || $parent_changed_entity;
+  }
+
+}

web/core/modules/workflows/src/Exception/RequiredStateMissingException.php

@@ -0,0 +1,11 @@
+<?php
+
+namespace Drupal\workflows\Exception;
+
+use Drupal\Core\Config\ConfigException;
+
+/**
+ * Indicates that a workflow does not contain a required state.
+ */
+class RequiredStateMissingException extends ConfigException {
+}

web/core/modules/workflows/src/Form/WorkflowAddForm.php

@@ -0,0 +1,116 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\Component\Plugin\PluginManagerInterface;
+use Drupal\workflows\Entity\Workflow;
+use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Form for adding workflows.
+ *
+ * @internal
+ */
+class WorkflowAddForm extends EntityForm {
+
+  /**
+   * The workflow type plugin manager.
+   *
+   * @var \Drupal\Component\Plugin\PluginManagerInterface
+   */
+  protected $workflowTypePluginManager;
+
+  /**
+   * WorkflowAddForm constructor.
+   *
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $workflow_type_plugin_manager
+   *   The workflow type plugin manager.
+   */
+  public function __construct(PluginManagerInterface $workflow_type_plugin_manager) {
+    $this->workflowTypePluginManager = $workflow_type_plugin_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin.manager.workflows.type')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $form = parent::form($form, $form_state);
+
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $form['label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Label'),
+      '#maxlength' => 255,
+      '#default_value' => $workflow->label(),
+      '#required' => TRUE,
+    ];
+
+    $form['id'] = [
+      '#type' => 'machine_name',
+      '#default_value' => $workflow->id(),
+      '#machine_name' => [
+        'exists' => [Workflow::class, 'load'],
+      ],
+    ];
+
+    $workflow_types = array_column($this->workflowTypePluginManager->getDefinitions(), 'label', 'id');
+
+    $form['workflow_type'] = [
+      '#type' => 'select',
+      '#title' => $this->t('Workflow type'),
+      '#required' => TRUE,
+      '#options' => $workflow_types,
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $return = $workflow->save();
+    if (empty($workflow->getTypePlugin()->getStates())) {
+      $this->messenger()->addStatus($this->t('Created the %label Workflow. In order for the workflow to be enabled there needs to be at least one state.', [
+        '%label' => $workflow->label(),
+      ]));
+      $form_state->setRedirectUrl($workflow->toUrl('add-state-form'));
+    }
+    else {
+      $this->messenger()->addStatus($this->t('Created the %label Workflow.', [
+        '%label' => $workflow->label(),
+      ]));
+      $form_state->setRedirectUrl($workflow->toUrl('edit-form'));
+    }
+    return $return;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
+    // This form can only set the workflow's ID, label and the weights for each
+    // state.
+    /** @var \Drupal\workflows\WorkflowInterface $entity */
+    $values = $form_state->getValues();
+    $entity->set('label', $values['label']);
+    $entity->set('id', $values['id']);
+    $entity->set('type', $values['workflow_type']);
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowDeleteForm.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\Core\Entity\EntityConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Url;
+
+/**
+ * Builds the form to delete Workflow entities.
+ *
+ * @internal
+ */
+class WorkflowDeleteForm extends EntityConfirmFormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    if ($this->entity->getTypePlugin()->workflowHasData($this->entity)) {
+      $form['#title'] = $this->getQuestion();
+      $form['description'] = ['#markup' => $this->t('This workflow is in use. You cannot remove this workflow until you have removed all content using it.')];
+      return $form;
+    }
+
+    return parent::buildForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Are you sure you want to delete %name?', ['%name' => $this->entity->label()]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return new Url('entity.workflow.collection');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConfirmText() {
+    return $this->t('Delete');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->entity->delete();
+
+    $this->messenger()->addStatus($this->t(
+      'Workflow %label deleted.',
+      ['%label' => $this->entity->label()]
+    ));
+
+    $form_state->setRedirectUrl($this->getCancelUrl());
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowEditForm.php

@@ -0,0 +1,283 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\Core\Form\SubformState;
+use Drupal\Core\Plugin\PluginFormFactoryInterface;
+use Drupal\workflows\Entity\Workflow;
+use Drupal\workflows\State;
+use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Url;
+use Drupal\workflows\WorkflowTypeInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * The form for editing workflows.
+ *
+ * @internal
+ */
+class WorkflowEditForm extends EntityForm {
+
+  /**
+   * The plugin form factory.
+   *
+   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
+   */
+  protected $pluginFormFactory;
+
+  /**
+   * Creates an instance of WorkflowStateEditForm.
+   *
+   * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $pluginFormFactory
+   *   The plugin form factory.
+   */
+  public function __construct(PluginFormFactoryInterface $pluginFormFactory) {
+    $this->pluginFormFactory = $pluginFormFactory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin_form.factory')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $form = parent::form($form, $form_state);
+
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+    $form['#title'] = $this->t('Edit %label workflow', ['%label' => $workflow->label()]);
+
+    $form['label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Label'),
+      '#maxlength' => 255,
+      '#default_value' => $workflow->label(),
+      '#required' => TRUE,
+    ];
+
+    $form['id'] = [
+      '#type' => 'machine_name',
+      '#default_value' => $workflow->id(),
+      '#machine_name' => [
+        'exists' => [Workflow::class, 'load'],
+      ],
+      '#disabled' => TRUE,
+    ];
+
+    $header = [
+      'state' => $this->t('State'),
+      'weight' => $this->t('Weight'),
+      'operations' => $this->t('Operations'),
+    ];
+    $form['states_container'] = [
+      '#type' => 'details',
+      '#title' => $this->t('States'),
+      '#open' => TRUE,
+    ];
+    $form['states_container']['states'] = [
+      '#type' => 'table',
+      '#header' => $header,
+      '#title' => $this->t('States'),
+      '#empty' => $this->t('There are no states yet.'),
+      '#tabledrag' => [
+        [
+          'action' => 'order',
+          'relationship' => 'sibling',
+          'group' => 'state-weight',
+        ],
+      ],
+    ];
+
+    $states = $workflow->getTypePlugin()->getStates();
+
+    // Warn the user if there are no states.
+    if (empty($states)) {
+      $this->messenger()->addWarning(
+        $this->t(
+          'This workflow has no states and will be disabled until there is at least one, <a href=":add-state">add a new state.</a>',
+          [':add-state' => $workflow->toUrl('add-state-form')->toString()]
+        )
+      );
+    }
+
+    $state_weight_delta = round(count($states) / 2);
+    foreach ($states as $state) {
+      $links = [
+        'edit' => [
+          'title' => $this->t('Edit'),
+          'url' => Url::fromRoute('entity.workflow.edit_state_form', ['workflow' => $workflow->id(), 'workflow_state' => $state->id()]),
+        ],
+      ];
+      if ($this->entity->access('delete-state:' . $state->id())) {
+        $links['delete'] = [
+          'title' => $this->t('Delete'),
+          'url' => Url::fromRoute('entity.workflow.delete_state_form', [
+            'workflow' => $workflow->id(),
+            'workflow_state' => $state->id(),
+          ]),
+        ];
+      }
+      $form['states_container']['states'][$state->id()] = [
+        '#attributes' => ['class' => ['draggable']],
+        'state' => ['#markup' => $state->label()],
+        '#weight' => $state->weight(),
+        'weight' => [
+          '#type' => 'weight',
+          '#title' => $this->t('Weight for @title', ['@title' => $state->label()]),
+          '#title_display' => 'invisible',
+          '#default_value' => $state->weight(),
+          '#attributes' => ['class' => ['state-weight']],
+          '#delta' => $state_weight_delta,
+        ],
+        'operations' => [
+          '#type' => 'operations',
+          '#links' => $links,
+        ],
+      ];
+    }
+    $form['states_container']['state_add'] = [
+      '#markup' => $workflow->toLink($this->t('Add a new state'), 'add-state-form')->toString(),
+    ];
+
+    $header = [
+      'label' => $this->t('Label'),
+      'weight' => $this->t('Weight'),
+      'from' => $this->t('From'),
+      'to' => $this->t('To'),
+      'operations' => $this->t('Operations'),
+    ];
+    $form['transitions_container'] = [
+      '#type' => 'details',
+      '#title' => $this->t('Transitions'),
+      '#open' => TRUE,
+    ];
+    $form['transitions_container']['transitions'] = [
+      '#type' => 'table',
+      '#header' => $header,
+      '#title' => $this->t('Transitions'),
+      '#empty' => $this->t('There are no transitions yet.'),
+      '#tabledrag' => [
+        [
+          'action' => 'order',
+          'relationship' => 'sibling',
+          'group' => 'transition-weight',
+        ],
+      ],
+    ];
+
+    $transitions = $workflow->getTypePlugin()->getTransitions();
+    $transition_weight_delta = round(count($transitions) / 2);
+    foreach ($transitions as $transition) {
+      $links['edit'] = [
+        'title' => $this->t('Edit'),
+        'url' => Url::fromRoute('entity.workflow.edit_transition_form', ['workflow' => $workflow->id(), 'workflow_transition' => $transition->id()]),
+      ];
+      $links['delete'] = [
+        'title' => $this->t('Delete'),
+        'url' => Url::fromRoute('entity.workflow.delete_transition_form', ['workflow' => $workflow->id(), 'workflow_transition' => $transition->id()]),
+      ];
+      $form['transitions_container']['transitions'][$transition->id()] = [
+        '#attributes' => ['class' => ['draggable']],
+        'label' => ['#markup' => $transition->label()],
+        '#weight' => $transition->weight(),
+        'weight' => [
+          '#type' => 'weight',
+          '#title' => $this->t('Weight for @title', ['@title' => $transition->label()]),
+          '#title_display' => 'invisible',
+          '#default_value' => $transition->weight(),
+          '#attributes' => ['class' => ['transition-weight']],
+          '#delta' => $transition_weight_delta,
+        ],
+        'from' => [
+          '#theme' => 'item_list',
+          '#items' => array_map([State::class, 'labelCallback'], $transition->from()),
+          '#context' => ['list_style' => 'comma-list'],
+        ],
+        'to' => ['#markup' => $transition->to()->label()],
+        'operations' => [
+          '#type' => 'operations',
+          '#links' => $links,
+        ],
+      ];
+    }
+    $form['transitions_container']['transition_add'] = [
+      '#markup' => $workflow->toLink($this->t('Add a new transition'), 'add-transition-form')->toString(),
+    ];
+
+    if ($workflow_type->hasFormClass(WorkflowTypeInterface::PLUGIN_FORM_KEY)) {
+      $form['type_settings'] = [
+        '#tree' => TRUE,
+      ];
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $form['type_settings'] += $this->pluginFormFactory
+        ->createInstance($workflow_type, WorkflowTypeInterface::PLUGIN_FORM_KEY)
+        ->buildConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+
+    if ($workflow_type->hasFormClass(WorkflowTypeInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, WorkflowTypeInterface::PLUGIN_FORM_KEY)
+        ->validateConfigurationForm($form['type_settings'], $subform_state);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+
+    if ($workflow_type->hasFormClass(WorkflowTypeInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, WorkflowTypeInterface::PLUGIN_FORM_KEY)
+        ->submitConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    $workflow->save();
+    $this->messenger()->addStatus($this->t('Saved the %label Workflow.', ['%label' => $workflow->label()]));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
+    // This form can only set the workflow's ID, label and the weights for each
+    // state.
+    /** @var \Drupal\workflows\WorkflowInterface $entity */
+    $values = $form_state->getValues();
+    $entity->set('label', $values['label']);
+    $entity->set('id', $values['id']);
+    foreach ($values['states'] as $state_id => $state_values) {
+      $entity->getTypePlugin()->setStateWeight($state_id, $state_values['weight']);
+    }
+    foreach ($values['transitions'] as $transition_id => $transition_values) {
+      $entity->getTypePlugin()->setTransitionWeight($transition_id, $transition_values['weight']);
+    }
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowStateAddForm.php

@@ -0,0 +1,181 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
+use Drupal\Core\Plugin\PluginFormFactoryInterface;
+use Drupal\workflows\StateInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Entity form variant for adding workflow states.
+ *
+ * @internal
+ */
+class WorkflowStateAddForm extends EntityForm {
+
+  /**
+   * The plugin form factory.
+   *
+   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
+   */
+  protected $pluginFormFactory;
+
+  /**
+   * Creates an instance of WorkflowStateEditForm.
+   *
+   * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $pluginFormFactory
+   *   The plugin form factory.
+   */
+  public function __construct(PluginFormFactoryInterface $pluginFormFactory) {
+    $this->pluginFormFactory = $pluginFormFactory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin_form.factory')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workflow_state_add_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $form = parent::form($form, $form_state);
+
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->getEntity();
+    $workflow_type = $workflow->getTypePlugin();
+
+    $form['label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('State label'),
+      '#maxlength' => 255,
+      '#default_value' => '',
+      '#required' => TRUE,
+    ];
+
+    $form['id'] = [
+      '#type' => 'machine_name',
+      '#machine_name' => [
+        'exists' => [$this, 'exists'],
+      ],
+    ];
+
+    if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
+      $form['type_settings'] = [
+        '#tree' => TRUE,
+      ];
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $form['type_settings'] += $this->pluginFormFactory
+        ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
+        ->buildConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    return $form;
+  }
+
+  /**
+   * Determines if the workflow state already exists.
+   *
+   * @param string $state_id
+   *   The workflow state ID.
+   *
+   * @return bool
+   *   TRUE if the workflow state exists, FALSE otherwise.
+   */
+  public function exists($state_id) {
+    /** @var \Drupal\workflows\WorkflowInterface $original_workflow */
+    $original_workflow = \Drupal::entityTypeManager()->getStorage('workflow')->loadUnchanged($this->getEntity()->id());
+    return $original_workflow->getTypePlugin()->hasState($state_id);
+  }
+
+  /**
+   * Copies top-level form values to entity properties.
+   *
+   * This form can only change values for a state, which is part of workflow.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity the current form should operate upon.
+   * @param array $form
+   *   A nested array of form elements comprising the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
+    if (!$form_state->isValidationComplete()) {
+      // Only do something once form validation is complete.
+      return;
+    }
+    /** @var \Drupal\workflows\WorkflowInterface $entity */
+    $values = $form_state->getValues();
+    $entity->getTypePlugin()->addState($values['id'], $values['label']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
+    /** @var \Drupal\workflows\WorkflowTypeInterface $workflow_type */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+
+    if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
+        ->validateConfigurationForm($form['type_settings'], $subform_state);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+    $state = $workflow_type->getState($form_state->getValue('id'));
+
+    if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('state', $state);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
+        ->submitConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    $workflow->save();
+    $this->messenger()->addStatus($this->t('Created %label state.', [
+      '%label' => $workflow->getTypePlugin()->getState($form_state->getValue('id'))->label(),
+    ]));
+    $form_state->setRedirectUrl($workflow->toUrl('edit-form'));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function actions(array $form, FormStateInterface $form_state) {
+    $actions['submit'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Save'),
+      '#submit' => ['::submitForm', '::save'],
+    ];
+    return $actions;
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowStateDeleteForm.php

@@ -0,0 +1,109 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\workflows\WorkflowInterface;
+use Drupal\Core\Form\ConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
+
+/**
+ * Builds the form to delete states from Workflow entities.
+ *
+ * @internal
+ */
+class WorkflowStateDeleteForm extends ConfirmFormBase {
+
+  /**
+   * The workflow entity the state being deleted belongs to.
+   *
+   * @var \Drupal\workflows\WorkflowInterface
+   */
+  protected $workflow;
+
+  /**
+   * The state being deleted.
+   *
+   * @var string
+   */
+  protected $stateId;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workflow_state_delete_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Are you sure you want to delete %state from %workflow?', ['%state' => $this->workflow->getTypePlugin()->getState($this->stateId)->label(), '%workflow' => $this->workflow->label()]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return $this->workflow->toUrl();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConfirmText() {
+    return $this->t('Delete');
+  }
+
+  /**
+   * Form constructor.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   * @param \Drupal\workflows\WorkflowInterface $workflow
+   *   The workflow entity being edited.
+   * @param string|null $workflow_state
+   *   The workflow state being deleted.
+   *
+   * @return array
+   *   The form structure.
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, ?WorkflowInterface $workflow = NULL, $workflow_state = NULL) {
+    if (!$workflow->getTypePlugin()->hasState($workflow_state)) {
+      throw new NotFoundHttpException();
+    }
+    $this->workflow = $workflow;
+    $this->stateId = $workflow_state;
+
+    if ($this->workflow->getTypePlugin()->workflowStateHasData($this->workflow, $this->workflow->getTypePlugin()->getState($this->stateId))) {
+      $form['#title'] = $this->getQuestion();
+      $form['description'] = ['#markup' => $this->t('This workflow state is in use. You cannot remove this workflow state until you have removed all content using it.')];
+      return $form;
+    }
+
+    return parent::buildForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+
+    $workflow_label = $this->workflow->getTypePlugin()->getState($this->stateId)->label();
+    $this->workflow
+      ->getTypePlugin()
+      ->deleteState($this->stateId);
+    $this->workflow->save();
+
+    $this->messenger()->addStatus($this->t(
+      'State %label deleted.',
+      ['%label' => $workflow_label]
+    ));
+
+    $form_state->setRedirectUrl($this->getCancelUrl());
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowStateEditForm.php

@@ -0,0 +1,240 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
+use Drupal\Core\Plugin\PluginFormFactoryInterface;
+use Drupal\Core\Url;
+use Drupal\workflows\StateInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Entity form variant for editing workflow states.
+ *
+ * @internal
+ */
+class WorkflowStateEditForm extends EntityForm {
+
+  /**
+   * The ID of the state that is being edited.
+   *
+   * @var string
+   */
+  protected $stateId;
+
+  /**
+   * The plugin form factory.
+   *
+   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
+   */
+  protected $pluginFormFactory;
+
+  /**
+   * Creates an instance of WorkflowStateEditForm.
+   *
+   * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $pluginFormFactory
+   *   The plugin form factory.
+   */
+  public function __construct(PluginFormFactoryInterface $pluginFormFactory) {
+    $this->pluginFormFactory = $pluginFormFactory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin_form.factory')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workflow_state_edit_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $workflow_state = NULL) {
+    $this->stateId = $workflow_state;
+    return parent::buildForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $form = parent::form($form, $form_state);
+
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->getEntity();
+    $workflow_type = $workflow->getTypePlugin();
+    $state = $workflow->getTypePlugin()->getState($this->stateId);
+
+    $form['label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('State label'),
+      '#maxlength' => 255,
+      '#default_value' => $state->label(),
+      '#required' => TRUE,
+    ];
+
+    $form['id'] = [
+      '#type' => 'machine_name',
+      '#default_value' => $this->stateId,
+      '#machine_name' => [
+        'exists' => [$this, 'exists'],
+      ],
+      '#disabled' => TRUE,
+    ];
+
+    // Add additional form fields from the workflow type plugin.
+    if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
+      $form['type_settings'] = [
+        '#tree' => TRUE,
+      ];
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('state', $state);
+      $form['type_settings'] += $this->pluginFormFactory
+        ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
+        ->buildConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    $header = [
+      'label' => $this->t('Transition'),
+      'state' => $this->t('To'),
+      'operations' => $this->t('Operations'),
+    ];
+    $form['transitions'] = [
+      '#type' => 'table',
+      '#header' => $header,
+      '#empty' => $this->t('There are no transitions to or from this state yet.'),
+    ];
+    foreach ($state->getTransitions() as $transition) {
+      $links['edit'] = [
+        'title' => $this->t('Edit'),
+        'url' => Url::fromRoute('entity.workflow.edit_transition_form', [
+          'workflow' => $workflow->id(),
+          'workflow_transition' => $transition->id(),
+        ]),
+      ];
+      $links['delete'] = [
+        'title' => $this->t('Delete'),
+        'url' => Url::fromRoute('entity.workflow.delete_transition_form', [
+          'workflow' => $workflow->id(),
+          'workflow_transition' => $transition->id(),
+        ]),
+      ];
+      $form['transitions'][$transition->id()] = [
+        'label' => [
+          '#markup' => $transition->label(),
+        ],
+        'state' => [
+          '#markup' => $transition->to()->label(),
+        ],
+        'operations' => [
+          '#type' => 'operations',
+          '#links' => $links,
+        ],
+      ];
+    }
+
+    return $form;
+  }
+
+  /**
+   * Copies top-level form values to entity properties.
+   *
+   * This form can only change values for a state, which is part of workflow.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity the current form should operate upon.
+   * @param array $form
+   *   A nested array of form elements comprising the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
+    if (!$form_state->isValidationComplete()) {
+      // Only do something once form validation is complete.
+      return;
+    }
+    /** @var \Drupal\workflows\WorkflowInterface $entity */
+    $values = $form_state->getValues();
+    $entity->getTypePlugin()->setStateLabel($values['id'], $values['label']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
+    /** @var \Drupal\workflows\WorkflowTypeInterface $workflow_type */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+
+    if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('state', $workflow_type->getState($this->stateId));
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
+        ->validateConfigurationForm($form['type_settings'], $subform_state);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+
+    if ($workflow_type->hasFormClass(StateInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('state', $workflow_type->getState($this->stateId));
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, StateInterface::PLUGIN_FORM_KEY)
+        ->submitConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    $workflow->save();
+    $this->messenger()->addStatus($this->t('Saved %label state.', [
+      '%label' => $workflow->getTypePlugin()->getState($this->stateId)->label(),
+    ]));
+    $form_state->setRedirectUrl($workflow->toUrl('edit-form'));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function actions(array $form, FormStateInterface $form_state) {
+    $actions['submit'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Save'),
+      '#submit' => ['::submitForm', '::save'],
+    ];
+
+    $actions['delete'] = [
+      '#type' => 'link',
+      '#title' => $this->t('Delete'),
+      '#access' => $this->entity->access('delete-state:' . $this->stateId),
+      '#attributes' => [
+        'class' => ['button', 'button--danger'],
+      ],
+      '#url' => Url::fromRoute('entity.workflow.delete_state_form', [
+        'workflow' => $this->entity->id(),
+        'workflow_state' => $this->stateId,
+      ]),
+    ];
+
+    return $actions;
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowTransitionAddForm.php

@@ -0,0 +1,209 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
+use Drupal\Core\Plugin\PluginFormFactoryInterface;
+use Drupal\workflows\State;
+use Drupal\workflows\TransitionInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Entity form variant for adding workflow transitions.
+ *
+ * @internal
+ */
+class WorkflowTransitionAddForm extends EntityForm {
+
+  /**
+   * The plugin form factory.
+   *
+   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
+   */
+  protected $pluginFormFactory;
+
+  /**
+   * Creates an instance of WorkflowStateEditForm.
+   *
+   * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $pluginFormFactory
+   *   The plugin form factory.
+   */
+  public function __construct(PluginFormFactoryInterface $pluginFormFactory) {
+    $this->pluginFormFactory = $pluginFormFactory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin_form.factory')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workflow_transition_add_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $form = parent::form($form, $form_state);
+
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->getEntity();
+    $workflow_type = $workflow->getTypePlugin();
+
+    $form['label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Transition label'),
+      '#maxlength' => 255,
+      '#default_value' => '',
+      '#required' => TRUE,
+    ];
+
+    $form['id'] = [
+      '#type' => 'machine_name',
+      '#machine_name' => [
+        'exists' => [$this, 'exists'],
+      ],
+    ];
+
+    // @todo https://www.drupal.org/node/2830584 Add some ajax to ensure that
+    //   only valid transitions are selectable.
+    $states = array_map([State::class, 'labelCallback'], $workflow->getTypePlugin()->getStates());
+    $form['from'] = [
+      '#type' => 'checkboxes',
+      '#title' => $this->t('From'),
+      '#required' => TRUE,
+      '#default_value' => [],
+      '#options' => $states,
+    ];
+    $form['to'] = [
+      '#type' => 'radios',
+      '#title' => $this->t('To'),
+      '#required' => TRUE,
+      '#options' => $states,
+    ];
+
+    // Add additional form fields from the workflow type plugin.
+    if ($workflow_type->hasFormClass(TransitionInterface::PLUGIN_FORM_KEY)) {
+      $form['type_settings'] = [
+        '#tree' => TRUE,
+      ];
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $form['type_settings'] += $this->pluginFormFactory
+        ->createInstance($workflow_type, TransitionInterface::PLUGIN_FORM_KEY)
+        ->buildConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    return $form;
+  }
+
+  /**
+   * Determines if the workflow transition already exists.
+   *
+   * @param string $transition_id
+   *   The workflow transition ID.
+   *
+   * @return bool
+   *   TRUE if the workflow transition exists, FALSE otherwise.
+   */
+  public function exists($transition_id) {
+    /** @var \Drupal\workflows\WorkflowInterface $original_workflow */
+    $original_workflow = \Drupal::entityTypeManager()->getStorage('workflow')->loadUnchanged($this->getEntity()->id());
+    return $original_workflow->getTypePlugin()->hasTransition($transition_id);
+  }
+
+  /**
+   * Copies top-level form values to entity properties.
+   *
+   * This form can only change values for a state, which is part of workflow.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity the current form should operate upon.
+   * @param array $form
+   *   A nested array of form elements comprising the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
+    if (!$form_state->isValidationComplete()) {
+      // Only do something once form validation is complete.
+      return;
+    }
+    /** @var \Drupal\workflows\WorkflowInterface $entity */
+    $values = $form_state->getValues();
+    $entity->getTypePlugin()->addTransition($values['id'], $values['label'], array_filter($values['from']), $values['to']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->getEntity();
+    $workflow_type = $workflow->getTypePlugin();
+
+    $values = $form_state->getValues();
+    foreach (array_filter($values['from']) as $from_state_id) {
+      if ($workflow->getTypePlugin()->hasTransitionFromStateToState($from_state_id, $values['to'])) {
+        $form_state->setErrorByName('from][' . $from_state_id, $this->t('The transition from %from to %to already exists.', [
+          '%from' => $workflow->getTypePlugin()->getState($from_state_id)->label(),
+          '%to' => $workflow->getTypePlugin()->getState($values['to'])->label(),
+        ]));
+      }
+    }
+
+    if ($workflow_type->hasFormClass(TransitionInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, TransitionInterface::PLUGIN_FORM_KEY)
+        ->validateConfigurationForm($form['type_settings'], $subform_state);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+    $transition = $workflow_type->getTransition($form_state->getValue('id'));
+
+    if ($workflow_type->hasFormClass(TransitionInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('transition', $transition);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, TransitionInterface::PLUGIN_FORM_KEY)
+        ->submitConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    $workflow->save();
+    $this->messenger()->addStatus($this->t('Created %label transition.', [
+      '%label' => $form_state->getValue('label'),
+    ]));
+    $form_state->setRedirectUrl($workflow->toUrl('edit-form'));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function actions(array $form, FormStateInterface $form_state) {
+    $actions['submit'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Save'),
+      '#submit' => ['::submitForm', '::save'],
+    ];
+    return $actions;
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowTransitionDeleteForm.php

@@ -0,0 +1,105 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\workflows\WorkflowInterface;
+use Drupal\Core\Form\ConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
+
+/**
+ * Builds the form to delete transitions from Workflow entities.
+ *
+ * @internal
+ */
+class WorkflowTransitionDeleteForm extends ConfirmFormBase {
+
+  /**
+   * The workflow entity the transition being deleted belongs to.
+   *
+   * @var \Drupal\workflows\WorkflowInterface
+   */
+  protected $workflow;
+
+  /**
+   * The workflow transition being deleted.
+   *
+   * @var \Drupal\workflows\TransitionInterface
+   */
+  protected $transition;
+
+  /**
+   * The transition being deleted.
+   *
+   * @var string
+   */
+  protected $transitionId;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workflow_transition_delete_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Are you sure you want to delete %transition from %workflow?', ['%transition' => $this->transition->label(), '%workflow' => $this->workflow->label()]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return $this->workflow->toUrl();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConfirmText() {
+    return $this->t('Delete');
+  }
+
+  /**
+   * Form constructor.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   * @param \Drupal\workflows\WorkflowInterface $workflow
+   *   The workflow entity being edited.
+   * @param string|null $workflow_transition
+   *   The workflow transition being deleted.
+   *
+   * @return array
+   *   The form structure.
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, ?WorkflowInterface $workflow = NULL, $workflow_transition = NULL) {
+    try {
+      $this->transition = $workflow->getTypePlugin()->getTransition($workflow_transition);
+    }
+    catch (\InvalidArgumentException $e) {
+      throw new NotFoundHttpException();
+    }
+    $this->workflow = $workflow;
+    return parent::buildForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->workflow
+      ->getTypePlugin()
+      ->deleteTransition($this->transition->id());
+    $this->workflow->save();
+
+    $this->messenger()->addStatus($this->t('%transition transition deleted.', ['%transition' => $this->transition->label()]));
+    $form_state->setRedirectUrl($this->getCancelUrl());
+  }
+
+}

web/core/modules/workflows/src/Form/WorkflowTransitionEditForm.php

@@ -0,0 +1,234 @@
+<?php
+
+namespace Drupal\workflows\Form;
+
+use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
+use Drupal\Core\Plugin\PluginFormFactoryInterface;
+use Drupal\Core\Url;
+use Drupal\workflows\State;
+use Drupal\workflows\TransitionInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Entity form variant for editing workflow transitions.
+ *
+ * @internal
+ */
+class WorkflowTransitionEditForm extends EntityForm {
+
+  /**
+   * The ID of the transition that is being edited.
+   *
+   * @var string
+   */
+  protected $transitionId;
+
+  /**
+   * The plugin form factory.
+   *
+   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
+   */
+  protected $pluginFormFactory;
+
+  /**
+   * Creates an instance of WorkflowStateEditForm.
+   *
+   * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $pluginFormFactory
+   *   The plugin form factory.
+   */
+  public function __construct(PluginFormFactoryInterface $pluginFormFactory) {
+    $this->pluginFormFactory = $pluginFormFactory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin_form.factory')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workflow_transition_edit_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $workflow_transition = NULL) {
+    $this->transitionId = $workflow_transition;
+    return parent::buildForm($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $form = parent::form($form, $form_state);
+
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->getEntity();
+    $workflow_type = $workflow->getTypePlugin();
+    $transition = $workflow->getTypePlugin()->getTransition($this->transitionId);
+
+    $form['label'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Transition label'),
+      '#maxlength' => 255,
+      '#default_value' => $transition->label(),
+      '#required' => TRUE,
+    ];
+
+    $form['id'] = [
+      '#type' => 'value',
+      '#value' => $this->transitionId,
+    ];
+
+    // @todo https://www.drupal.org/node/2830584 Add some ajax to ensure that
+    //   only valid transitions are selectable.
+    $states = array_map([State::class, 'labelCallback'], $workflow->getTypePlugin()->getStates());
+    $form['from'] = [
+      '#type' => 'checkboxes',
+      '#title' => $this->t('From'),
+      '#required' => TRUE,
+      '#default_value' => array_keys($transition->from()),
+      '#options' => $states,
+    ];
+    $form['to'] = [
+      '#type' => 'radios',
+      '#title' => $this->t('To'),
+      '#required' => TRUE,
+      '#default_value' => $transition->to()->id(),
+      '#options' => $states,
+      '#disabled' => TRUE,
+    ];
+
+    // Add additional form fields from the workflow type plugin.
+    if ($workflow_type->hasFormClass(TransitionInterface::PLUGIN_FORM_KEY)) {
+      $form['type_settings'] = [
+        '#tree' => TRUE,
+      ];
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('transition', $transition);
+      $form['type_settings'] += $this->pluginFormFactory
+        ->createInstance($workflow_type, TransitionInterface::PLUGIN_FORM_KEY)
+        ->buildConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->getEntity();
+    $workflow_type = $workflow->getTypePlugin();
+    $transition = $workflow_type->getTransition($this->transitionId);
+
+    $values = $form_state->getValues();
+    foreach (array_filter($values['from']) as $from_state_id) {
+      if ($workflow_type->hasTransitionFromStateToState($from_state_id, $values['to'])) {
+        $existing_transition = $workflow_type->getTransitionFromStateToState($from_state_id, $values['to']);
+        if ($existing_transition->id() !== $values['id']) {
+          $form_state->setErrorByName('from][' . $from_state_id, $this->t('The transition from %from to %to already exists.', [
+            '%from' => $workflow->getTypePlugin()->getState($from_state_id)->label(),
+            '%to' => $workflow->getTypePlugin()->getState($values['to'])->label(),
+          ]));
+        }
+      }
+    }
+
+    if ($workflow_type->hasFormClass(TransitionInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('transition', $transition);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, TransitionInterface::PLUGIN_FORM_KEY)
+        ->validateConfigurationForm($form['type_settings'], $subform_state);
+    }
+  }
+
+  /**
+   * Copies top-level form values to entity properties.
+   *
+   * This form can only change values for a state, which is part of workflow.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity the current form should operate upon.
+   * @param array $form
+   *   A nested array of form elements comprising the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
+    if (!$form_state->isValidationComplete()) {
+      // Only do something once form validation is complete.
+      return;
+    }
+    /** @var \Drupal\workflows\WorkflowInterface $entity */
+    $values = $form_state->getValues();
+    $form_state->set('created_transition', FALSE);
+    $entity->getTypePlugin()->setTransitionLabel($values['id'], $values['label']);
+    $entity->getTypePlugin()->setTransitionFromStates($values['id'], array_filter($values['from']));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    /** @var \Drupal\workflows\WorkflowInterface $workflow */
+    $workflow = $this->entity;
+    $workflow_type = $workflow->getTypePlugin();
+    $transition = $workflow_type->getTransition($this->transitionId);
+
+    if ($workflow_type->hasFormClass(TransitionInterface::PLUGIN_FORM_KEY)) {
+      $subform_state = SubformState::createForSubform($form['type_settings'], $form, $form_state);
+      $subform_state->set('transition', $transition);
+      $this->pluginFormFactory
+        ->createInstance($workflow_type, TransitionInterface::PLUGIN_FORM_KEY)
+        ->submitConfigurationForm($form['type_settings'], $subform_state);
+    }
+
+    $workflow->save();
+    $this->messenger()->addStatus($this->t('Saved %label transition.', [
+      '%label' => $workflow->getTypePlugin()->getTransition($this->transitionId)->label(),
+    ]));
+    $form_state->setRedirectUrl($workflow->toUrl('edit-form'));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function actions(array $form, FormStateInterface $form_state) {
+    $actions['submit'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Save'),
+      '#submit' => ['::submitForm', '::save'],
+    ];
+
+    $actions['delete'] = [
+      '#type' => 'link',
+      '#title' => $this->t('Delete'),
+      // Deleting a transition is editing a workflow.
+      '#access' => $this->entity->access('edit'),
+      '#attributes' => [
+        'class' => ['button', 'button--danger'],
+      ],
+      '#url' => Url::fromRoute('entity.workflow.delete_transition_form', [
+        'workflow' => $this->entity->id(),
+        'workflow_transition' => $this->transitionId,
+      ]),
+    ];
+
+    return $actions;
+  }
+
+}

web/core/modules/workflows/src/Plugin/WorkflowTypeBase.php

@@ -0,0 +1,464 @@
+<?php
+
+namespace Drupal\workflows\Plugin;
+
+use Drupal\Component\Plugin\PluginBase;
+use Drupal\Core\Plugin\PluginWithFormsTrait;
+use Drupal\workflows\State;
+use Drupal\workflows\StateInterface;
+use Drupal\workflows\Transition;
+use Drupal\workflows\TransitionInterface;
+use Drupal\workflows\WorkflowInterface;
+use Drupal\workflows\WorkflowTypeInterface;
+
+/**
+ * A base class for Workflow type plugins.
+ *
+ * @see \Drupal\workflows\Annotation\WorkflowType
+ */
+abstract class WorkflowTypeBase extends PluginBase implements WorkflowTypeInterface {
+
+  use PluginWithFormsTrait;
+
+  /**
+   * A regex for matching a valid state/transition machine name.
+   */
+  const VALID_ID_REGEX = '/[^a-z0-9_]+/';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->setConfiguration($configuration);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function label() {
+    $definition = $this->getPluginDefinition();
+    // The label can be an object.
+    // @see \Drupal\Core\StringTranslation\TranslatableMarkup
+    return $definition['label'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function workflowHasData(WorkflowInterface $workflow) {
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function workflowStateHasData(WorkflowInterface $workflow, StateInterface $state) {
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConfiguration() {
+    return $this->configuration;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setConfiguration(array $configuration) {
+    $this->configuration = $configuration + $this->defaultConfiguration();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRequiredStates() {
+    return $this->getPluginDefinition()['required_states'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return [
+      'states' => [],
+      'transitions' => [],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function calculateDependencies() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function onDependencyRemoval(array $dependencies) {
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getInitialState() {
+    $ordered_states = $this->getStates();
+    return reset($ordered_states);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addState($state_id, $label) {
+    if ($this->hasState($state_id)) {
+      throw new \InvalidArgumentException("The state '$state_id' already exists in workflow.");
+    }
+    if (preg_match(static::VALID_ID_REGEX, $state_id)) {
+      throw new \InvalidArgumentException("The state ID '$state_id' must contain only lowercase letters, numbers, and underscores");
+    }
+    $this->configuration['states'][$state_id] = [
+      'label' => $label,
+      'weight' => $this->getNextWeight($this->configuration['states']),
+    ];
+    ksort($this->configuration['states']);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasState($state_id) {
+    return isset($this->configuration['states'][$state_id]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getStates($state_ids = NULL) {
+    if ($state_ids === NULL) {
+      $state_ids = array_keys($this->configuration['states']);
+    }
+    /** @var \Drupal\workflows\StateInterface[] $states */
+    $states = array_combine($state_ids, array_map([$this, 'getState'], $state_ids));
+    return static::labelWeightMultisort($states);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getState($state_id) {
+    if (!isset($this->configuration['states'][$state_id])) {
+      throw new \InvalidArgumentException("The state '$state_id' does not exist in workflow.");
+    }
+    return new State(
+      $this,
+      $state_id,
+      $this->configuration['states'][$state_id]['label'],
+      $this->configuration['states'][$state_id]['weight']
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setStateLabel($state_id, $label) {
+    if (!$this->hasState($state_id)) {
+      throw new \InvalidArgumentException("The state '$state_id' does not exist in workflow.");
+    }
+    $this->configuration['states'][$state_id]['label'] = $label;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setStateWeight($state_id, $weight) {
+    if (!$this->hasState($state_id)) {
+      throw new \InvalidArgumentException("The state '$state_id' does not exist in workflow.");
+    }
+    if (!is_numeric($weight)) {
+      $label = $this->getState($state_id)->label();
+      throw new \InvalidArgumentException("The weight '$weight' must be numeric for state '$label'.");
+    }
+    $this->configuration['states'][$state_id]['weight'] = $weight;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function deleteState($state_id) {
+    if (!$this->hasState($state_id)) {
+      throw new \InvalidArgumentException("The state '$state_id' does not exist in workflow.");
+    }
+    if (count($this->configuration['states']) === 1) {
+      throw new \InvalidArgumentException("The state '$state_id' can not be deleted from workflow as it is the only state.");
+    }
+
+    foreach ($this->configuration['transitions'] as $transition_id => $transition) {
+      if ($transition['to'] === $state_id) {
+        $this->deleteTransition($transition_id);
+        continue;
+      }
+      $from_key = array_search($state_id, $transition['from'], TRUE);
+      if ($from_key !== FALSE) {
+        // Remove state from the from array.
+        unset($transition['from'][$from_key]);
+        if (empty($transition['from'])) {
+          // There are no more 'from' entries, remove the transition.
+          $this->deleteTransition($transition_id);
+          continue;
+        }
+        // We changed the from state, update the transition.
+        $this->setTransitionFromStates($transition_id, $transition['from']);
+      }
+    }
+    unset($this->configuration['states'][$state_id]);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function addTransition($transition_id, $label, array $from_state_ids, $to_state_id) {
+    if ($this->hasTransition($transition_id)) {
+      throw new \InvalidArgumentException("The transition '$transition_id' already exists in workflow.");
+    }
+    if (preg_match(static::VALID_ID_REGEX, $transition_id)) {
+      throw new \InvalidArgumentException("The transition ID '$transition_id' must contain only lowercase letters, numbers, and underscores.");
+    }
+
+    if (!$this->hasState($to_state_id)) {
+      throw new \InvalidArgumentException("The state '$to_state_id' does not exist in workflow.");
+    }
+    $this->configuration['transitions'][$transition_id] = [
+      'label' => $label,
+      'from' => [],
+      'to' => $to_state_id,
+      // Always add to the end.
+      'weight' => $this->getNextWeight($this->configuration['transitions']),
+    ];
+
+    try {
+      $this->setTransitionFromStates($transition_id, $from_state_ids);
+    }
+    catch (\InvalidArgumentException $e) {
+      unset($this->configuration['transitions'][$transition_id]);
+      throw $e;
+    }
+
+    ksort($this->configuration['transitions']);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTransitions(?array $transition_ids = NULL) {
+    if ($transition_ids === NULL) {
+      $transition_ids = array_keys($this->configuration['transitions']);
+    }
+    /** @var \Drupal\workflows\TransitionInterface[] $transitions */
+    $transitions = array_combine($transition_ids, array_map([$this, 'getTransition'], $transition_ids));
+    return static::labelWeightMultisort($transitions);
+  }
+
+  /**
+   * Sort states or transitions by weight, label, and key.
+   *
+   * @param \Drupal\workflows\StateInterface[]|\Drupal\workflows\TransitionInterface[] $objects
+   *   An array of state or transition objects to multi-sort, keyed by the
+   *   state or transition ID.
+   *
+   * @return \Drupal\workflows\StateInterface[]|\Drupal\workflows\TransitionInterface[]
+   *   An array of sorted transitions or states, keyed by the state or
+   *   transition ID.
+   */
+  protected static function labelWeightMultisort($objects) {
+    if (count($objects) > 1) {
+      // Separate weights, labels, and keys into arrays.
+      $weights = $labels = [];
+      $keys = array_keys($objects);
+      foreach ($objects as $id => $object) {
+        $weights[$id] = $object->weight();
+        $labels[$id] = $object->label();
+      }
+      // Sort weights, labels, and keys in the same order as each other.
+      array_multisort(
+      // Use the numerical weight as the primary sort.
+        $weights, SORT_NUMERIC, SORT_ASC,
+        // When objects have the same weight, sort them alphabetically by label.
+        $labels, SORT_NATURAL, SORT_ASC,
+        // Ensure that the keys (the object IDs) are sorted in the same order as
+        // the weights.
+        $keys
+      );
+      // Combine keys and weights to make sure the weights are keyed with the
+      // correct keys.
+      $weights = array_combine($keys, $weights);
+      // Return the objects sorted by weight.
+      return array_replace($weights, $objects);
+    }
+    return $objects;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTransition($transition_id) {
+    if (!$this->hasTransition($transition_id)) {
+      throw new \InvalidArgumentException("The transition '$transition_id' does not exist in workflow.");
+    }
+    return new Transition(
+      $this,
+      $transition_id,
+      $this->configuration['transitions'][$transition_id]['label'],
+      $this->configuration['transitions'][$transition_id]['from'],
+      $this->configuration['transitions'][$transition_id]['to'],
+      $this->configuration['transitions'][$transition_id]['weight']
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasTransition($transition_id) {
+    return isset($this->configuration['transitions'][$transition_id]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTransitionsForState($state_id, $direction = TransitionInterface::DIRECTION_FROM) {
+    $transition_ids = array_keys(array_filter($this->configuration['transitions'], function ($transition) use ($state_id, $direction) {
+      return in_array($state_id, (array) $transition[$direction], TRUE);
+    }));
+    return $this->getTransitions($transition_ids);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTransitionFromStateToState($from_state_id, $to_state_id) {
+    $transition_id = $this->getTransitionIdFromStateToState($from_state_id, $to_state_id);
+    if (empty($transition_id)) {
+      throw new \InvalidArgumentException("The transition from '$from_state_id' to '$to_state_id' does not exist in workflow.");
+    }
+    return $this->getTransition($transition_id);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasTransitionFromStateToState($from_state_id, $to_state_id) {
+    return $this->getTransitionIdFromStateToState($from_state_id, $to_state_id) !== NULL;
+  }
+
+  /**
+   * Gets the transition ID from state to state.
+   *
+   * @param string $from_state_id
+   *   The state ID to transition from.
+   * @param string $to_state_id
+   *   The state ID to transition to.
+   *
+   * @return string|null
+   *   The transition ID, or NULL if no transition exists.
+   */
+  protected function getTransitionIdFromStateToState($from_state_id, $to_state_id) {
+    foreach ($this->configuration['transitions'] as $transition_id => $transition) {
+      if (in_array($from_state_id, $transition['from'], TRUE) && $transition['to'] === $to_state_id) {
+        return $transition_id;
+      }
+    }
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setTransitionLabel($transition_id, $label) {
+    if (!$this->hasTransition($transition_id)) {
+      throw new \InvalidArgumentException("The transition '$transition_id' does not exist in workflow.");
+    }
+    $this->configuration['transitions'][$transition_id]['label'] = $label;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setTransitionWeight($transition_id, $weight) {
+    if (!$this->hasTransition($transition_id)) {
+      throw new \InvalidArgumentException("The transition '$transition_id' does not exist in workflow.");
+    }
+    if (!is_numeric($weight)) {
+      $label = $this->getTransition($transition_id)->label();
+      throw new \InvalidArgumentException("The weight '$weight' must be numeric for transition '$label'.");
+    }
+    $this->configuration['transitions'][$transition_id]['weight'] = $weight;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setTransitionFromStates($transition_id, array $from_state_ids) {
+    if (!$this->hasTransition($transition_id)) {
+      throw new \InvalidArgumentException("The transition '$transition_id' does not exist in workflow.");
+    }
+
+    // Ensure that the states exist.
+    foreach ($from_state_ids as $from_state_id) {
+      if (!$this->hasState($from_state_id)) {
+        throw new \InvalidArgumentException("The state '$from_state_id' does not exist in workflow.");
+      }
+      if ($this->hasTransitionFromStateToState($from_state_id, $this->configuration['transitions'][$transition_id]['to'])) {
+        $existing_transition_id = $this->getTransitionIdFromStateToState($from_state_id, $this->configuration['transitions'][$transition_id]['to']);
+        if ($transition_id !== $existing_transition_id) {
+          throw new \InvalidArgumentException("The '$existing_transition_id' transition already allows '$from_state_id' to '{$this->configuration['transitions'][$transition_id]['to']}' transitions in workflow.");
+        }
+      }
+    }
+
+    // Preserve the order of the state IDs in the from value and don't save any
+    // keys.
+    $from_state_ids = array_values($from_state_ids);
+    sort($from_state_ids);
+    $this->configuration['transitions'][$transition_id]['from'] = $from_state_ids;
+
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function deleteTransition($transition_id) {
+    if (!$this->hasTransition($transition_id)) {
+      throw new \InvalidArgumentException("The transition '$transition_id' does not exist in workflow.");
+    }
+    unset($this->configuration['transitions'][$transition_id]);
+    return $this;
+  }
+
+  /**
+   * Gets the weight for a new state or transition.
+   *
+   * @param array $items
+   *   An array of states or transitions information where each item has a
+   *   'weight' key with a numeric value.
+   *
+   * @return int
+   *   The weight for a new item in the array so that it has the highest weight.
+   */
+  protected function getNextWeight(array $items) {
+    return array_reduce($items, function ($carry, $item) {
+      return max($carry, $item['weight'] + 1);
+    }, 0);
+  }
+
+}

web/core/modules/workflows/src/Plugin/WorkflowTypeConfigureFormBase.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\workflows\Plugin;
+
+use Drupal\Component\Plugin\PluginAwareInterface;
+use Drupal\Component\Plugin\PluginInspectionInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginFormInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+
+/**
+ * A base class for workflow type configuration forms.
+ */
+abstract class WorkflowTypeConfigureFormBase implements PluginFormInterface, PluginAwareInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The workflow type.
+   *
+   * @var \Drupal\workflows\WorkflowTypeInterface
+   */
+  protected $workflowType;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setPlugin(PluginInspectionInterface $plugin) {
+    $this->workflowType = $plugin;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
+  }
+
+}

web/core/modules/workflows/src/Plugin/WorkflowTypeStateFormBase.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace Drupal\workflows\Plugin;
+
+use Drupal\Component\Plugin\PluginAwareInterface;
+use Drupal\Component\Plugin\PluginInspectionInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginFormInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+
+/**
+ * A base class for workflow type state forms.
+ */
+abstract class WorkflowTypeStateFormBase implements PluginFormInterface, PluginAwareInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The workflow type.
+   *
+   * @var \Drupal\workflows\WorkflowTypeInterface
+   */
+  protected $workflowType;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setPlugin(PluginInspectionInterface $plugin) {
+    $this->workflowType = $plugin;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    $values = $form_state->getValues();
+    $state = $form_state->get('state');
+    $configuration = $this->workflowType->getConfiguration();
+    $configuration['states'][$state->id()] = $values + $configuration['states'][$state->id()];
+    $this->workflowType->setConfiguration($configuration);
+  }
+
+}

web/core/modules/workflows/src/Plugin/WorkflowTypeTransitionFormBase.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace Drupal\workflows\Plugin;
+
+use Drupal\Component\Plugin\PluginAwareInterface;
+use Drupal\Component\Plugin\PluginInspectionInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginFormInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+
+/**
+ * A base class for workflow type transition forms.
+ */
+abstract class WorkflowTypeTransitionFormBase implements PluginFormInterface, PluginAwareInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The workflow type.
+   *
+   * @var \Drupal\workflows\WorkflowTypeInterface
+   */
+  protected $workflowType;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setPlugin(PluginInspectionInterface $plugin) {
+    $this->workflowType = $plugin;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    $values = $form_state->getValues();
+    $transition = $form_state->get('transition');
+    $configuration = $this->workflowType->getConfiguration();
+    $configuration['transitions'][$transition->id()] = $values + $configuration['transitions'][$transition->id()];
+    $this->workflowType->setConfiguration($configuration);
+  }
+
+}

web/core/modules/workflows/src/State.php

@@ -0,0 +1,115 @@
+<?php
+
+namespace Drupal\workflows;
+
+/**
+ * A value object representing a workflow state.
+ */
+class State implements StateInterface {
+
+  /**
+   * The workflow the state is attached to.
+   *
+   * @var \Drupal\workflows\WorkflowTypeInterface
+   */
+  protected $workflow;
+
+  /**
+   * The state's ID.
+   *
+   * @var string
+   */
+  protected $id;
+
+  /**
+   * The state's label.
+   *
+   * @var string
+   */
+  protected $label;
+
+  /**
+   * The state's weight.
+   *
+   * @var int
+   */
+  protected $weight;
+
+  /**
+   * State constructor.
+   *
+   * @param \Drupal\workflows\WorkflowTypeInterface $workflow
+   *   The workflow the state is attached to.
+   * @param string $id
+   *   The state's ID.
+   * @param string $label
+   *   The state's label.
+   * @param int $weight
+   *   The state's weight.
+   */
+  public function __construct(WorkflowTypeInterface $workflow, $id, $label, $weight = 0) {
+    $this->workflow = $workflow;
+    $this->id = $id;
+    $this->label = $label;
+    $this->weight = $weight;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function id() {
+    return $this->id;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function label() {
+    return $this->label;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function weight() {
+    return $this->weight;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function canTransitionTo($to_state_id) {
+    return $this->workflow->hasTransitionFromStateToState($this->id, $to_state_id);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTransitionTo($to_state_id) {
+    if (!$this->canTransitionTo($to_state_id)) {
+      throw new \InvalidArgumentException("Can not transition to '$to_state_id' state");
+    }
+    return $this->workflow->getTransitionFromStateToState($this->id(), $to_state_id);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTransitions() {
+    return $this->workflow->getTransitionsForState($this->id);
+  }
+
+  /**
+   * Helper method to convert a State value object to a label.
+   *
+   * @param \Drupal\workflows\StateInterface $state
+   *   The state.
+   *
+   * @return string
+   *   The label of the state.
+   */
+  public static function labelCallback(StateInterface $state) {
+    return $state->label();
+  }
+
+}

web/core/modules/workflows/src/StateInterface.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace Drupal\workflows;
+
+/**
+ * An interface for state value objects.
+ *
+ * @internal
+ *   The StateInterface should only be used by Workflows and Content Moderation.
+ * @todo Revisit the need for this in https://www.drupal.org/node/2902309.
+ */
+interface StateInterface {
+
+  /**
+   * The key of the state plugin form.
+   */
+  const PLUGIN_FORM_KEY = 'state';
+
+  /**
+   * Gets the state's ID.
+   *
+   * @return string
+   *   The state's ID.
+   */
+  public function id();
+
+  /**
+   * Gets the state's label.
+   *
+   * @return string
+   *   The state's label.
+   */
+  public function label();
+
+  /**
+   * Gets the state's weight.
+   *
+   * @return int
+   *   The state's weight.
+   */
+  public function weight();
+
+  /**
+   * Determines if the state can transition to the provided state ID.
+   *
+   * @param $to_state_id
+   *   The state to transition to.
+   *
+   * @return bool
+   *   TRUE if the state can transition to the provided state ID. FALSE, if not.
+   */
+  public function canTransitionTo($to_state_id);
+
+  /**
+   * Gets the Transition object for the provided state ID.
+   *
+   * @param $to_state_id
+   *   The state to transition to.
+   *
+   * @return \Drupal\workflows\TransitionInterface
+   *   The Transition object for the provided state ID.
+   *
+   * @throws \InvalidArgumentException()
+   *   Exception thrown when the provided state ID can not be transitioned to.
+   */
+  public function getTransitionTo($to_state_id);
+
+  /**
+   * Gets all the possible transition objects for the state.
+   *
+   * @return \Drupal\workflows\TransitionInterface[]
+   *   All the possible transition objects for the state.
+   */
+  public function getTransitions();
+
+}

web/core/modules/workflows/src/Transition.php

@@ -0,0 +1,112 @@
+<?php
+
+namespace Drupal\workflows;
+
+/**
+ * A transition value object that describes the transition between states.
+ */
+class Transition implements TransitionInterface {
+
+  /**
+   * The workflow that this transition is attached to.
+   *
+   * @var \Drupal\workflows\WorkflowTypeInterface
+   */
+  protected $workflow;
+
+  /**
+   * The transition's ID.
+   *
+   * @var string
+   */
+  protected $id;
+
+  /**
+   * The transition's label.
+   *
+   * @var string
+   */
+  protected $label;
+
+  /**
+   * The transition's from state IDs.
+   *
+   * @var string[]
+   */
+  protected $fromStateIds;
+
+  /**
+   * The transition's to state ID.
+   *
+   * @var string
+   */
+  protected $toStateId;
+
+  /**
+   * The transition's weight.
+   *
+   * @var int
+   */
+  protected $weight;
+
+  /**
+   * Transition constructor.
+   *
+   * @param \Drupal\workflows\WorkflowTypeInterface $workflow
+   *   The workflow the state is attached to.
+   * @param string $id
+   *   The transition's ID.
+   * @param string $label
+   *   The transition's label.
+   * @param array $from_state_ids
+   *   A list of from state IDs.
+   * @param string $to_state_id
+   *   The to state ID.
+   * @param int $weight
+   *   (optional) The transition's weight. Defaults to 0.
+   */
+  public function __construct(WorkflowTypeInterface $workflow, $id, $label, array $from_state_ids, $to_state_id, $weight = 0) {
+    $this->workflow = $workflow;
+    $this->id = $id;
+    $this->label = $label;
+    $this->fromStateIds = $from_state_ids;
+    $this->toStateId = $to_state_id;
+    $this->weight = $weight;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function id() {
+    return $this->id;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function label() {
+    return $this->label;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function from() {
+    return $this->workflow->getStates($this->fromStateIds);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function to() {
+    return $this->workflow->getState($this->toStateId);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function weight() {
+    return $this->weight;
+  }
+
+}

web/core/modules/workflows/src/TransitionInterface.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace Drupal\workflows;
+
+/**
+ * A transition value object that describes the transition between two states.
+ *
+ * @internal
+ *   The TransitionInterface should only be used by Workflows and Content
+ *   Moderation.
+ *
+ * @todo Revisit the need for this in https://www.drupal.org/node/2902309.
+ */
+interface TransitionInterface {
+
+  /**
+   * The key of the transition plugin form.
+   */
+  const PLUGIN_FORM_KEY = 'transition';
+
+  /**
+   * The transition direction from.
+   */
+  const DIRECTION_FROM = 'from';
+
+  /**
+   * The transition direction to.
+   */
+  const DIRECTION_TO = 'to';
+
+  /**
+   * Gets the transition's ID.
+   *
+   * @return string
+   *   The transition's ID.
+   */
+  public function id();
+
+  /**
+   * Gets the transition's label.
+   *
+   * @return string
+   *   The transition's label.
+   */
+  public function label();
+
+  /**
+   * Gets the transition's from states.
+   *
+   * @return \Drupal\workflows\StateInterface[]
+   *   The transition's from states.
+   */
+  public function from();
+
+  /**
+   * Gets the transition's to state.
+   *
+   * @return \Drupal\workflows\StateInterface
+   *   The transition's to state.
+   */
+  public function to();
+
+  /**
+   * Gets the transition's weight.
+   *
+   * @return string
+   *   The transition's weight.
+   */
+  public function weight();
+
+}

web/core/modules/workflows/src/WorkflowAccessControlHandler.php

@@ -0,0 +1,82 @@
+<?php
+
+namespace Drupal\workflows;
+
+use Drupal\Component\Plugin\PluginManagerInterface;
+use Drupal\Core\Entity\EntityAccessControlHandler;
+use Drupal\Core\Entity\EntityHandlerInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\Access\AccessResult;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Access controller for the Workflow entity.
+ *
+ * @see \Drupal\workflows\Entity\Workflow.
+ */
+class WorkflowAccessControlHandler extends EntityAccessControlHandler implements EntityHandlerInterface {
+
+  /**
+   * The workflow type plugin manager.
+   *
+   * @var \Drupal\Component\Plugin\PluginManagerInterface
+   */
+  protected $workflowTypeManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    return new static(
+      $entity_type,
+      $container->get('plugin.manager.workflows.type')
+    );
+  }
+
+  /**
+   * Constructs the workflow access control handler instance.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $workflow_type_manager
+   *   The workflow type plugin manager.
+   */
+  public function __construct(EntityTypeInterface $entity_type, PluginManagerInterface $workflow_type_manager) {
+    parent::__construct($entity_type);
+    $this->workflowTypeManager = $workflow_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkAccess(EntityInterface $entity, $operation, AccountInterface $account) {
+    /** @var \Drupal\workflows\Entity\Workflow $entity */
+    $workflow_type = $entity->getTypePlugin();
+    if (str_starts_with($operation, 'delete-state')) {
+      [, $state_id] = explode(':', $operation, 2);
+      // Deleting a state is editing a workflow, but also we should forbid
+      // access if there is only one state.
+      return AccessResult::allowedIf(count($entity->getTypePlugin()->getStates()) > 1)
+        ->andIf(parent::checkAccess($entity, 'edit', $account))
+        ->andIf(AccessResult::allowedIf(!in_array($state_id, $workflow_type->getRequiredStates(), TRUE)))
+        ->addCacheableDependency($entity);
+    }
+
+    return parent::checkAccess($entity, $operation, $account);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkCreateAccess(AccountInterface $account, array $context, $entity_bundle = NULL) {
+    $workflow_types_count = count($this->workflowTypeManager->getDefinitions());
+    $admin_access = parent::checkCreateAccess($account, $context, $entity_bundle);
+    // Allow access if there is at least one workflow type. Since workflow types
+    // are provided by modules this is cacheable until extensions change.
+    return $admin_access
+      ->andIf(AccessResult::allowedIf($workflow_types_count > 0));
+  }
+
+}

web/core/modules/workflows/src/WorkflowInterface.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Drupal\workflows;
+
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
+
+/**
+ * Provides an interface for defining workflow entities.
+ */
+interface WorkflowInterface extends ConfigEntityInterface {
+
+  /**
+   * Gets the workflow type plugin.
+   *
+   * @return \Drupal\workflows\WorkflowTypeInterface
+   *   The workflow type plugin.
+   */
+  public function getTypePlugin();
+
+}

web/core/modules/workflows/src/WorkflowListBuilder.php

@@ -0,0 +1,102 @@
+<?php
+
+namespace Drupal\workflows;
+
+use Drupal\Component\Plugin\PluginManagerInterface;
+use Drupal\Core\Config\Entity\ConfigEntityListBuilder;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Url;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a listing of Workflow entities.
+ */
+class WorkflowListBuilder extends ConfigEntityListBuilder {
+
+  /**
+   * The workflow type plugin manager.
+   *
+   * @var \Drupal\Component\Plugin\PluginManagerInterface
+   */
+  protected $workflowTypeManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    return new static(
+      $entity_type,
+      $container->get('entity_type.manager')->getStorage($entity_type->id()),
+      $container->get('plugin.manager.workflows.type')
+    );
+  }
+
+  /**
+   * Constructs a new WorkflowListBuilder object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
+   *   The entity storage class.
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $workflow_type_manager
+   *   The workflow type plugin manager.
+   */
+  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, PluginManagerInterface $workflow_type_manager) {
+    parent::__construct($entity_type, $storage);
+    $this->workflowTypeManager = $workflow_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'workflow_admin_overview_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildHeader() {
+    $header['label'] = $this->t('Workflow');
+    $header['type'] = $this->t('Type');
+    $header['states'] = $this->t('States');
+
+    return $header + parent::buildHeader();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildRow(EntityInterface $entity) {
+    /** @var \Drupal\workflows\WorkflowInterface $entity */
+    $row['label'] = $entity->label();
+
+    $row['type']['data'] = [
+      '#markup' => $entity->getTypePlugin()->label(),
+    ];
+
+    $items = array_map([State::class, 'labelCallback'], $entity->getTypePlugin()->getStates());
+    $row['states']['data'] = [
+      '#theme' => 'item_list',
+      '#context' => ['list_style' => 'comma-list'],
+      '#items' => $items,
+    ];
+
+    return $row + parent::buildRow($entity);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function render() {
+    $build = parent::render();
+    $workflow_types_count = count($this->workflowTypeManager->getDefinitions());
+    if ($workflow_types_count === 0) {
+      $build['table']['#empty'] = $this->t('There are no workflow types available. In order to create workflows you need to install a module that provides a workflow type. For example, the <a href=":content-moderation">Content Moderation</a> module provides a workflow type that enables workflows for content entities.', [':content-moderation' => Url::fromRoute('system.modules_list', [], ['fragment' => 'module-content-moderation'])->toString()]);
+    }
+    return $build;
+  }
+
+}

web/core/modules/workflows/src/WorkflowStateTransitionOperationsAccessCheck.php

@@ -0,0 +1,84 @@
+<?php
+
+namespace Drupal\workflows;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Routing\Access\AccessInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Provides an access check for state and transition operations.
+ */
+class WorkflowStateTransitionOperationsAccessCheck implements AccessInterface {
+
+  /**
+   * Checks access for operations of workflow states and transitions.
+   *
+   * The value of '_workflow_access' is used to check to kind of access that
+   * should be applied to a route in the context of a workflow and a state or
+   * transition. States and transitions can individually have access control
+   * applied to them for 'add', 'update' and 'delete'. By default workflows will
+   * use the admin permission 'administer workflows' for all of these
+   * operations, except for delete-state which checks there is at least one
+   * state, a state does not have data and it's not a required state.
+   *
+   * For the update and delete operations, a workflow and a state or transition
+   * is required in the route for the access check to be applied. For the "add"
+   * operation, only a workflow is required. The '_workflow_access' requirement
+   * translates into access checks on the workflow entity type in the formats:
+   *   - @code"$operation-state:$state_id"@endcode
+   *   - @code"$operation-transition:$transition_id"@endcode
+   *
+   * For example the following route definition with the path
+   * "/test-workflow/foo-state/delete" the 'delete-state:foo-state' operation
+   * will be checked:
+   * @code
+   * pattern: '/{workflow}/{workflow_state}/delete'
+   * requirements:
+   *   _workflow_access: 'delete-state'
+   * @endcode
+   *
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The parametrized route
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The currently logged in account.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   An access result.
+   *
+   * @throws \Exception
+   *   Throws an exception when a route is defined with an invalid operation.
+   */
+  public function access(RouteMatchInterface $route_match, AccountInterface $account) {
+    $workflow_operation = $this->getOperation($route_match);
+    if (!preg_match('/^(?<operation>add|update|delete)-(?<type>state|transition)$/', $workflow_operation, $matches)) {
+      throw new \Exception("Invalid _workflow_access operation '$workflow_operation' specified for route '{$route_match->getRouteName()}'.");
+    }
+
+    $parameters = $route_match->getParameters();
+    $workflow = $parameters->get('workflow');
+    if ($workflow && $matches['operation'] === 'add') {
+      return $workflow->access($workflow_operation, $account, TRUE);
+    }
+    if ($workflow && $type = $parameters->get(sprintf('workflow_%s', $matches['type']))) {
+      return $workflow->access(sprintf('%s:%s', $workflow_operation, $type), $account, TRUE);
+    }
+
+    return AccessResult::neutral();
+  }
+
+  /**
+   * Get the operation that will be used for the access check.
+   *
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The parametrized route
+   *
+   * @return string
+   *   The access operation.
+   */
+  protected function getOperation(RouteMatchInterface $route_match) {
+    return $route_match->getRouteObject()->getRequirement('_workflow_access');
+  }
+
+}

web/core/modules/workflows/src/WorkflowTypeInterface.php

@@ -0,0 +1,352 @@
+<?php
+
+namespace Drupal\workflows;
+
+use Drupal\Component\Plugin\ConfigurableInterface;
+use Drupal\Component\Plugin\DependentPluginInterface;
+use Drupal\Component\Plugin\DerivativeInspectionInterface;
+use Drupal\Core\Plugin\PluginWithFormsInterface;
+
+/**
+ * An interface for Workflow type plugins.
+ */
+interface WorkflowTypeInterface extends PluginWithFormsInterface, DerivativeInspectionInterface, ConfigurableInterface, DependentPluginInterface {
+
+  /**
+   * The key of the global workflow plugin form.
+   */
+  const PLUGIN_FORM_KEY = 'configure';
+
+  /**
+   * Gets the label for the workflow type.
+   *
+   * @return string
+   *   The workflow type label.
+   */
+  public function label();
+
+  /**
+   * Determines if the workflow is being has data associated with it.
+   *
+   * @internal
+   *   Marked as internal until it's validated this should form part of the
+   *   public API in https://www.drupal.org/node/2897148.
+   *
+   * @param \Drupal\workflows\WorkflowInterface $workflow
+   *   The workflow to check.
+   *
+   * @return bool
+   *   TRUE if the workflow is being used, FALSE if not.
+   */
+  public function workflowHasData(WorkflowInterface $workflow);
+
+  /**
+   * Determines if the workflow state has data associated with it.
+   *
+   * @internal
+   *   Marked as internal until it's validated this should form part of the
+   *   public API in https://www.drupal.org/node/2897148.
+   *
+   * @param \Drupal\workflows\WorkflowInterface $workflow
+   *   The workflow to check.
+   * @param \Drupal\workflows\StateInterface $state
+   *   The workflow state to check.
+   *
+   * @return bool
+   *   TRUE if the workflow state is being used, FALSE if not.
+   */
+  public function workflowStateHasData(WorkflowInterface $workflow, StateInterface $state);
+
+  /**
+   * Gets the initial state for the workflow.
+   *
+   * @return \Drupal\workflows\StateInterface
+   *   The initial state.
+   */
+  public function getInitialState();
+
+  /**
+   * Gets the required states of workflow type.
+   *
+   * This is usually specified in the workflow type annotation.
+   *
+   * @return string[]
+   *   The required states.
+   *
+   * @see \Drupal\workflows\Annotation\WorkflowType
+   */
+  public function getRequiredStates();
+
+  /**
+   * Informs the plugin that a dependency of the workflow will be deleted.
+   *
+   * @param array $dependencies
+   *   An array of dependencies that will be deleted keyed by dependency type.
+   *
+   * @return bool
+   *   TRUE if the workflow settings have been changed, FALSE if not.
+   *
+   * @see \Drupal\Core\Config\ConfigEntityInterface::onDependencyRemoval()
+   *
+   * @todo https://www.drupal.org/node/2579743 make part of a generic interface.
+   */
+  public function onDependencyRemoval(array $dependencies);
+
+  /**
+   * Adds a state to the workflow.
+   *
+   * @param string $state_id
+   *   The state's ID.
+   * @param string $label
+   *   The state's label.
+   *
+   * @return $this
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if a state already exists or state ID is invalid.
+   */
+  public function addState($state_id, $label);
+
+  /**
+   * Determines if the workflow has a state with the provided ID.
+   *
+   * @param string $state_id
+   *   The state's ID.
+   *
+   * @return bool
+   *   TRUE if the workflow has a state with the provided ID, FALSE if not.
+   */
+  public function hasState($state_id);
+
+  /**
+   * Gets state objects for the provided state IDs.
+   *
+   * @param string[] $state_ids
+   *   A list of state IDs to get. If NULL then all states will be returned.
+   *
+   * @return \Drupal\workflows\StateInterface[]
+   *   An array of workflow states, keyed by state IDs.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if $state_ids contains a state ID that does not exist.
+   */
+  public function getStates($state_ids = NULL);
+
+  /**
+   * Gets a workflow state.
+   *
+   * @param string $state_id
+   *   The state's ID.
+   *
+   * @return \Drupal\workflows\StateInterface
+   *   The workflow state.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if $state_id does not exist.
+   */
+  public function getState($state_id);
+
+  /**
+   * Sets a state's label.
+   *
+   * @param string $state_id
+   *   The state ID to set the label for.
+   * @param string $label
+   *   The state's label.
+   *
+   * @return $this
+   */
+  public function setStateLabel($state_id, $label);
+
+  /**
+   * Sets a state's weight value.
+   *
+   * @param string $state_id
+   *   The state ID to set the weight for.
+   * @param int $weight
+   *   The state's weight.
+   *
+   * @return $this
+   */
+  public function setStateWeight($state_id, $weight);
+
+  /**
+   * Deletes a state from the workflow.
+   *
+   * @param string $state_id
+   *   The state ID to delete.
+   *
+   * @return $this
+   *   The workflow type plugin.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if $state_id does not exist.
+   */
+  public function deleteState($state_id);
+
+  /**
+   * Adds a transition to the workflow.
+   *
+   * @param string $id
+   *   The transition ID.
+   * @param string $label
+   *   The transition's label.
+   * @param array $from_state_ids
+   *   The state IDs to transition from.
+   * @param string $to_state_id
+   *   The state ID to transition to.
+   *
+   * @return $this
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if either state does not exist.
+   */
+  public function addTransition($id, $label, array $from_state_ids, $to_state_id);
+
+  /**
+   * Gets a transition object for the provided transition ID.
+   *
+   * @param string $transition_id
+   *   A transition ID.
+   *
+   * @return \Drupal\workflows\TransitionInterface
+   *   The transition.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if $transition_id does not exist.
+   */
+  public function getTransition($transition_id);
+
+  /**
+   * Determines if a transition exists.
+   *
+   * @param string $transition_id
+   *   The transition ID.
+   *
+   * @return bool
+   *   TRUE if the transition exists, FALSE if not.
+   */
+  public function hasTransition($transition_id);
+
+  /**
+   * Gets transition objects for the provided transition IDs.
+   *
+   * @param string[] $transition_ids
+   *   A list of transition IDs to get. If NULL then all transitions will be
+   *   returned.
+   *
+   * @return \Drupal\workflows\TransitionInterface[]
+   *   An array of transition objects.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if $transition_ids contains a transition ID that does not exist.
+   */
+  public function getTransitions(?array $transition_ids = NULL);
+
+  /**
+   * Gets the transitions for a state for the provided direction.
+   *
+   * @param $state_id
+   *   The state to get transitions for.
+   * @param string $direction
+   *   (optional) The direction of the transition, defaults to
+   *   TransitionInterface::DIRECTION_FROM. Possible values are:
+   *   TransitionInterface::DIRECTION_FROM or TransitionInterface::DIRECTION_TO.
+   *
+   * @return \Drupal\workflows\TransitionInterface[]
+   *   An array of the transition objects for the state in the given direction,
+   *   keyed by transition ID.
+   *
+   * @see \Drupal\workflows\TransitionInterface::DIRECTION_FROM
+   * @see \Drupal\workflows\TransitionInterface::DIRECTION_TO
+   */
+  public function getTransitionsForState($state_id, $direction = TransitionInterface::DIRECTION_FROM);
+
+  /**
+   * Gets a transition from state to state.
+   *
+   * @param string $from_state_id
+   *   The state ID to transition from.
+   * @param string $to_state_id
+   *   The state ID to transition to.
+   *
+   * @return \Drupal\workflows\TransitionInterface
+   *   The transitions.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if the transition does not exist.
+   */
+  public function getTransitionFromStateToState($from_state_id, $to_state_id);
+
+  /**
+   * Determines if a transition from state to state exists.
+   *
+   * @param string $from_state_id
+   *   The state ID to transition from.
+   * @param string $to_state_id
+   *   The state ID to transition to.
+   *
+   * @return bool
+   *   TRUE if the transition exists, FALSE if not.
+   */
+  public function hasTransitionFromStateToState($from_state_id, $to_state_id);
+
+  /**
+   * Sets a transition's label.
+   *
+   * @param string $transition_id
+   *   The transition ID.
+   * @param string $label
+   *   The transition's label.
+   *
+   * @return $this
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if the transition does not exist.
+   */
+  public function setTransitionLabel($transition_id, $label);
+
+  /**
+   * Sets a transition's weight.
+   *
+   * @param string $transition_id
+   *   The transition ID.
+   * @param int $weight
+   *   The transition's weight.
+   *
+   * @return $this
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if the transition does not exist.
+   */
+  public function setTransitionWeight($transition_id, $weight);
+
+  /**
+   * Sets a transition's from states.
+   *
+   * @param string $transition_id
+   *   The transition ID.
+   * @param array $from_state_ids
+   *   The state IDs to transition from.
+   *
+   * @return $this
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if the transition does not exist or the states do not exist.
+   */
+  public function setTransitionFromStates($transition_id, array $from_state_ids);
+
+  /**
+   * Deletes a transition.
+   *
+   * @param string $transition_id
+   *   The transition ID.
+   *
+   * @return $this
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown if the transition does not exist.
+   */
+  public function deleteTransition($transition_id);
+
+}

web/core/modules/workflows/src/WorkflowTypeManager.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Drupal\workflows;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Plugin\DefaultPluginManager;
+use Drupal\workflows\Attribute\WorkflowType;
+
+/**
+ * Provides a Workflow type plugin manager.
+ *
+ * @see \Drupal\workflows\Annotation\WorkflowType
+ * @see \Drupal\workflows\WorkflowTypeInterface
+ * @see plugin_api
+ */
+class WorkflowTypeManager extends DefaultPluginManager {
+
+  /**
+   * Constructs a new class instance.
+   *
+   * @param \Traversable $namespaces
+   *   An object that implements \Traversable which contains the root paths
+   *   keyed by the corresponding namespace to look for plugin implementations.
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
+   *   Cache backend instance to use.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler to invoke the alter hook with.
+   */
+  public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler) {
+    parent::__construct('Plugin/WorkflowType', $namespaces, $module_handler, WorkflowTypeInterface::class, WorkflowType::class, 'Drupal\workflows\Annotation\WorkflowType');
+    $this->alterInfo('workflow_type_info');
+    $this->setCacheBackend($cache_backend, 'workflow_type_info');
+  }
+
+}