Warn in comment field if task is closed as duplicate

Summary:
Display a placeholder text in the text comment field of a Maniphest task if the task status has been set to Duplicate.
This makes it clearer to users (who may have not checked the task status at the top of the page) not to fragment conversations.

Closes T15749

Test Plan:
* Be logged in and go to a task which is closed as a duplicate and see the placeholder text in the field to add a comment.
* Be logged in and go to tasks which are not closed as a duplicate and see no placeholder text in the field to add a comment.
* Go to other places whose code calls a `PhabricatorApplicationTransactionCommentView` constructor and check that it still renders correctly, for example Ponder in http://phorge.localhost/Q1, Slowvote in http://phorge.localhost/V1, Differential in http://phorge.localhost/D1

Reviewers: O1 Blessed Committers, valerio.bozzolan, avivey

Reviewed By: O1 Blessed Committers, valerio.bozzolan, avivey

Subscribers: avivey, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15749

Differential Revision: https://we.phorge.it/D25546

src/applications/maniphest/editor/ManiphestEditEngine.php

@@ -69,6 +69,14 @@ final class ManiphestEditEngine
     return pht('Set Sail for Adventure');
   }
 
+  public function getCommentFieldPlaceholderText($object) {
+    if ($object->getStatus() === ManiphestTaskStatus::STATUS_CLOSED_DUPLICATE) {
+      return pht('This task is closed as a duplicate. '.
+      'Only comment if you think that this task is not a duplicate.');
+    }
+    return '';
+  }
+
   protected function getObjectViewURI($object) {
     return '/'.$object->getMonogram();
   }

src/applications/pholio/controller/PholioMockViewController.php

@@ -223,7 +223,7 @@ final class PholioMockViewController extends PholioController {
 
     $form = id(new PhabricatorApplicationTransactionCommentView())
       ->setUser($viewer)
-      ->setObjectPHID($mock->getPHID())
+      ->setObject($mock)
       ->setFormID($comment_form_id)
       ->setDraft($draft)
       ->setHeaderText($title)

src/applications/ponder/controller/PonderQuestionViewController.php

@@ -60,7 +60,7 @@ final class PonderQuestionViewController extends PonderController {
 
     $add_comment = id(new PhabricatorApplicationTransactionCommentView())
       ->setUser($viewer)
-      ->setObjectPHID($question->getPHID())
+      ->setObject($question)
       ->setShowPreview(false)
       ->setAction($this->getApplicationURI("/question/comment/{$id}/"))
       ->setSubmitButtonName(pht('Comment'));

src/applications/ponder/view/PonderAnswerView.php

@@ -121,7 +121,7 @@ final class PonderAnswerView extends AphrontTagView {
 
     $comment_view = id(new PhabricatorApplicationTransactionCommentView())
       ->setUser($viewer)
-      ->setObjectPHID($answer->getPHID())
+      ->setObject($answer)
       ->setShowPreview(false)
       ->setHeaderText(pht('Answer Comment'))
       ->setAction("/ponder/answer/comment/{$id}/")

src/applications/slowvote/controller/PhabricatorSlowvotePollController.php

@@ -154,7 +154,7 @@ final class PhabricatorSlowvotePollController
 
     return id(new PhabricatorApplicationTransactionCommentView())
       ->setUser($viewer)
-      ->setObjectPHID($poll->getPHID())
+      ->setObject($poll)
       ->setDraft($draft)
       ->setHeaderText($add_comment_header)
       ->setAction($this->getApplicationURI('/comment/'.$poll->getID().'/'))

src/applications/transactions/editengine/PhabricatorEditEngine.php

@@ -339,7 +339,17 @@ abstract class PhabricatorEditEngine
     return null;
   }
 
-
+  /**
+   * Set default placeholder plain text in the comment textarea of the engine.
+   * To be overwritten by conditions defined in the child EditEngine class.
+   *
+   * @param  object Object in which the comment textarea is displayed.
+   * @return string Placeholder text to display in the comment textarea.
+   * @task text
+   */
+  public function getCommentFieldPlaceholderText($object) {
+    return '';
+  }
 
   /**
    * Return a human-readable header describing what this engine is used to do,
@@ -1664,10 +1674,11 @@ abstract class PhabricatorEditEngine
 
     $view = id(new PhabricatorApplicationTransactionCommentView())
       ->setUser($viewer)
-      ->setObjectPHID($object_phid)
       ->setHeaderText($header_text)
       ->setAction($comment_uri)
       ->setRequiresMFA($requires_mfa)
+      ->setObject($object)
+      ->setEditEngine($this)
       ->setSubmitButtonName($button_text);
 
     $draft = PhabricatorVersionedDraft::loadDraft(

src/applications/transactions/view/PhabricatorApplicationTransactionCommentView.php

@@ -15,11 +15,12 @@ final class PhabricatorApplicationTransactionCommentView
   private $draft;
   private $requestURI;
   private $showPreview = true;
-  private $objectPHID;
+  private $object;
   private $headerText;
   private $noPermission;
   private $fullWidth;
   private $infoView;
+  private $editEngine;
   private $editEngineLock;
   private $noBorder;
   private $requiresMFA;
@@ -30,13 +31,19 @@ final class PhabricatorApplicationTransactionCommentView
   private $commentActionGroups = array();
   private $transactionTimeline;
 
-  public function setObjectPHID($object_phid) {
-    $this->objectPHID = $object_phid;
+  /**
+   * Set object in which this comment textarea field is displayed
+   */
+  public function setObject($object) {
+    $this->object = $object;
     return $this;
   }
 
-  public function getObjectPHID() {
-    return $this->objectPHID;
+  /**
+   * Get object in which this comment textarea is displayed
+   */
+  public function getObject() {
+    return $this->object;
   }
 
   public function setShowPreview($show_preview) {
@@ -150,6 +157,15 @@ final class PhabricatorApplicationTransactionCommentView
     return $this->noPermission;
   }
 
+  public function setEditEngine(PhabricatorEditEngine $edit_engine) {
+    $this->editEngine = $edit_engine;
+    return $this;
+  }
+
+  public function getEditEngine() {
+    return $this->editEngine;
+  }
+
   public function setEditEngineLock(PhabricatorEditEngineLock $lock) {
     $this->editEngineLock = $lock;
     return $this;
@@ -295,6 +311,15 @@ final class PhabricatorApplicationTransactionCommentView
 
   private function renderCommentPanel() {
     $viewer = $this->getViewer();
+    $engine = $this->getEditEngine();
+    // In a few rare cases PhabricatorApplicationTransactionCommentView gets
+    // initiated in a View or Controller class. Don't crash in that case.
+    if ($engine) {
+      $placeholder_text = $engine
+        ->getCommentFieldPlaceholderText($this->getObject());
+    } else {
+      $placeholder_text = '';
+    }
 
     $remarkup_control = id(new PhabricatorRemarkupControl())
       ->setViewer($viewer)
@@ -302,6 +327,7 @@ final class PhabricatorApplicationTransactionCommentView
       ->addClass('phui-comment-fullwidth-control')
       ->addClass('phui-comment-textarea-control')
       ->setCanPin(true)
+      ->setPlaceholder($placeholder_text)
       ->setName('comment');
 
     $draft_comment = '';
@@ -331,7 +357,7 @@ final class PhabricatorApplicationTransactionCommentView
     }
     $remarkup_control->setRemarkupMetadata($draft_metadata);
 
-    if (!$this->getObjectPHID()) {
+    if (!$this->getObject()->getPHID()) {
       throw new PhutilInvalidStateException('setObjectPHID', 'render');
     }
 
@@ -345,7 +371,7 @@ final class PhabricatorApplicationTransactionCommentView
       ->setFullWidth($this->fullWidth)
       ->setMetadata(
         array(
-          'objectPHID' => $this->getObjectPHID(),
+          'objectPHID' => $this->getObject()->getPHID(),
         ))
       ->setAction($this->getAction())
       ->setID($this->getFormID())