Improve messaging of special policy rules in applications

Summary: Ref T603. When the user encounters an action which is controlled by a special policy rule in the application, make it easier for applications to show the user what policy controls the action and what the setting is. I took this about halfway before and left a TODO, but turn it into something more useful.

Test Plan: See screenshots.

Reviewers: btrahan, chad

Reviewed By: chad

CC: chad, aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7265

src/applications/base/controller/PhabricatorController.php

@@ -364,9 +364,46 @@ abstract class PhabricatorController extends AphrontController {
       $capability);
   }
 
-  protected function explainApplicationCapability($capability, $message) {
-    // TODO: Render a link to get more information.
-    return $message;
+  protected function explainApplicationCapability(
+    $capability,
+    $positive_message,
+    $negative_message) {
+
+    $can_act = $this->hasApplicationCapability($capability);
+    if ($can_act) {
+      $message = $positive_message;
+      $icon_name = 'enable-grey';
+    } else {
+      $message = $negative_message;
+      $icon_name = 'lock';
+    }
+
+    $icon = id(new PHUIIconView())
+      ->setSpriteSheet(PHUIIconView::SPRITE_ICONS)
+      ->setSpriteIcon($icon_name);
+
+    require_celerity_resource('policy-css');
+
+    $phid = $this->getCurrentApplication()->getPHID();
+    $explain_uri = "/policy/explain/{$phid}/{$capability}/";
+
+    $message = phutil_tag(
+      'div',
+      array(
+        'class' => 'policy-capability-explanation',
+      ),
+      array(
+        $icon,
+        javelin_tag(
+          'a',
+          array(
+            'href' => $explain_uri,
+            'sigil' => 'workflow',
+          ),
+          $message),
+      ));
+
+    return array($can_act, $message);
   }
 
 }