Don't show workboard action previews if the action won't have any effect

Summary:
Ref T10335. When you (for example) drag a "Resolved" task into a column with "Trigger: change status to resolved.", don't show a hint that the action will "Change status to resolved." since this isn't helpful and is somewhat confusing.

For now, the only visibility operator is "!=" since all current actions are simple field comparisons, but some actions in the future (like "add subscriber" or "remove project") might need other conditions.

Test Plan:
Dragged cards in ways that previously provided useless hints: move from column A to column B on a "Group by Priority" board; drag a resolved task to a "Trigger: change status to as resolved" column. Saw a more accurate preview in both cases.

Drags which actually cause effects still show the effects correctly.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T10335

Differential Revision: https://secure.phabricator.com/D20300

src/applications/project/controller/PhabricatorProjectBoardViewController.php

@@ -655,6 +655,8 @@ final class PhabricatorProjectBoardViewController
       $properties[$task->getPHID()] = array(
         'points' => (double)$task->getPoints(),
         'status' => $task->getStatus(),
+        'priority' => (int)$task->getPriority(),
+        'owner' => $task->getOwnerPHID(),
       );
     }
 

src/applications/project/icon/PhabricatorProjectDropEffect.php

@@ -6,6 +6,7 @@ final class PhabricatorProjectDropEffect
   private $icon;
   private $color;
   private $content;
+  private $conditions = array();
 
   public function setIcon($icon) {
     $this->icon = $icon;
@@ -39,7 +40,22 @@ final class PhabricatorProjectDropEffect
       'icon' => $this->getIcon(),
       'color' => $this->getColor(),
       'content' => hsprintf('%s', $this->getContent()),
+      'conditions' => $this->getConditions(),
     );
   }
 
+  public function addCondition($field, $operator, $value) {
+    $this->conditions[] = array(
+      'field' => $field,
+      'operator' => $operator,
+      'value' => $value,
+    );
+
+    return $this;
+  }
+
+  public function getConditions() {
+    return $this->conditions;
+  }
+
 }

src/applications/project/order/PhabricatorProjectColumnOwnerOrder.php

@@ -171,6 +171,7 @@ final class PhabricatorProjectColumnOwnerOrder
           $this->newEffect()
             ->setIcon($owner_icon)
             ->setColor($owner_color)
+            ->addCondition('owner', '!=', $owner_phid)
             ->setContent($effect_content));
       }
 

src/applications/project/order/PhabricatorProjectColumnPriorityOrder.php

@@ -68,6 +68,7 @@ final class PhabricatorProjectColumnPriorityOrder
       $drop_effect = $this->newEffect()
         ->setIcon($priority_icon)
         ->setColor($priority_color)
+        ->addCondition('priority', '!=', $priority)
         ->setContent(
           pht(
             'Change priority to %s.',

src/applications/project/order/PhabricatorProjectColumnStatusOrder.php

@@ -75,6 +75,7 @@ final class PhabricatorProjectColumnStatusOrder
       $drop_effect = $this->newEffect()
         ->setIcon($status_icon)
         ->setColor($status_color)
+        ->addCondition('status', '!=', $status_key)
         ->setContent(
           pht(
             'Change status to %s.',

src/applications/project/trigger/PhabricatorProjectTriggerManiphestStatusRule.php

@@ -51,6 +51,7 @@ final class PhabricatorProjectTriggerManiphestStatusRule
       $this->newEffect()
         ->setIcon($status_icon)
         ->setColor($status_color)
+        ->addCondition('status', '!=', $value)
         ->setContent($content),
     );
   }