Allow applications to test if a user could edit a certain field by clicking "Edit Thing"

Summary: See D15432. There, we can use this test to check if the user //could// reassign the task by using "Edit Form" or the stacked actions, so any dedicated "claim" element is consistent with the other permissions.

Test Plan:
  - Added a `var_dump($can_reassign)` after the call.
  - Saw `true`.
  - Edited the edit form, locked and disabled "Assigned To".
  - Saw `false`.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D15433

src/applications/maniphest/controller/ManiphestTaskDetailController.php

@@ -26,6 +26,10 @@ final class ManiphestTaskDetailController extends ManiphestController {
       ->setViewer($viewer)
       ->readFieldsFromStorage($task);
 
+    $edit_engine = id(new ManiphestEditEngine())
+      ->setViewer($viewer)
+      ->setTargetObject($task);
+
     $e_commit = ManiphestTaskHasCommitEdgeType::EDGECONST;
     $e_dep_on = ManiphestTaskDependsOnTaskEdgeType::EDGECONST;
     $e_dep_by = ManiphestTaskDependedOnByTaskEdgeType::EDGECONST;
@@ -73,12 +77,11 @@ final class ManiphestTaskDetailController extends ManiphestController {
     $header = $this->buildHeaderView($task);
     $details = $this->buildPropertyView($task, $field_list, $edges, $handles);
     $description = $this->buildDescriptionView($task, $engine);
-    $curtain = $this->buildCurtain($task);
+    $curtain = $this->buildCurtain($task, $edit_engine);
 
     $title = pht('%s %s', $monogram, $task->getTitle());
 
-    $comment_view = id(new ManiphestEditEngine())
+    $comment_view = $edit_engine
-      ->setViewer($viewer)
       ->buildEditEngineCommentView($task);
 
     $timeline->setQuoteRef($monogram);
@@ -146,7 +149,9 @@ final class ManiphestTaskDetailController extends ManiphestController {
   }
 
 
-  private function buildCurtain(ManiphestTask $task) {
+  private function buildCurtain(
+    ManiphestTask $task,
+    PhabricatorEditEngine $edit_engine) {
     $viewer = $this->getViewer();
 
     $id = $task->getID();
@@ -176,11 +181,12 @@ final class ManiphestTaskDetailController extends ManiphestController {
         ->setDisabled(!$can_edit)
         ->setWorkflow(true));
 
-    $edit_config = id(new ManiphestEditEngine())
+    $edit_config = $edit_engine->loadDefaultEditConfiguration();
-      ->setViewer($viewer)
-      ->loadDefaultEditConfiguration();
-
     $can_create = (bool)$edit_config;
+
+    $can_reassign = $edit_engine->hasEditAccessToTransaction(
+      ManiphestTransaction::TYPE_OWNER);
+
     if ($can_create) {
       $form_key = $edit_config->getIdentifier();
       $edit_uri = id(new PhutilURI("/task/edit/form/{$form_key}/"))

src/applications/transactions/editengine/PhabricatorEditEngine.php

@@ -821,7 +821,7 @@ abstract class PhabricatorEditEngine
   }
 
   private function buildCrumbs($object, $final = false) {
-    $controller = $this->getcontroller();
+    $controller = $this->getController();
 
     $crumbs = $controller->buildApplicationCrumbsForEditEngine();
     if ($this->getIsCreate()) {
@@ -1179,6 +1179,60 @@ abstract class PhabricatorEditEngine
     return $actions;
   }
 
+
+  /**
+   * Test if the viewer could apply a certain type of change by using the
+   * normal "Edit" form.
+   *
+   * This method returns `true` if the user has access to an edit form and
+   * that edit form has a field which applied the specified transaction type,
+   * and that field is visible and editable for the user.
+   *
+   * For example, you can use it to test if a user is able to reassign tasks
+   * or not, prior to rendering dedicated UI for task reassingment.
+   *
+   * Note that this method does NOT test if the user can actually edit the
+   * current object, just if they have access to the related field.
+   *
+   * @param const Transaction type to test for.
+   * @return bool True if the user could "Edit" to apply the transaction type.
+   */
+  final public function hasEditAccessToTransaction($xaction_type) {
+    $viewer = $this->getViewer();
+
+    $config = $this->loadDefaultEditConfiguration();
+    if (!$config) {
+      return false;
+    }
+
+    $object = $this->getTargetObject();
+    if (!$object) {
+      $object = $this->newEditableObject();
+    }
+
+    $fields = $this->buildEditFields($object);
+
+    $field = null;
+    foreach ($fields as $form_field) {
+      $field_xaction_type = $form_field->getTransactionType();
+      if ($field_xaction_type === $xaction_type) {
+        $field = $form_field;
+        break;
+      }
+    }
+
+    if (!$field) {
+      return false;
+    }
+
+    if (!$field->shouldReadValueFromSubmit()) {
+      return false;
+    }
+
+    return true;
+  }
+
+
   final public function addActionToCrumbs(PHUICrumbsView $crumbs) {
     $viewer = $this->getViewer();