Fix missing link targets for "View Object" header buttons in HTML email

Summary:
See <https://discourse.phabricator-community.org/t/view-task-from-maniphest-e-mail-doesnt-have-url/2827>.

I added "View Task" / "View Commit" buttons recently but the logic for generating URIs isn't quite right. Fix it up.

Test Plan:
  - Commented on a task.
  - Used `bin/mail show-outbound --id ... --dump-html > out.html` to dump the HTML.
  - Previewed the HTML in a browser.
  - This time, actually clicked the button to go to the task.

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D20586

src/applications/audit/editor/PhabricatorAuditEditor.php

@@ -485,7 +485,8 @@ final class PhabricatorAuditEditor
     return $phids;
   }
 
-  protected function getObjectLinkButtonLabelForMail() {
+  protected function getObjectLinkButtonLabelForMail(
+    PhabricatorLiskDAO $object) {
     return pht('View Commit');
   }
 

src/applications/differential/editor/DifferentialTransactionEditor.php

@@ -601,7 +601,8 @@ final class DifferentialTransactionEditor
     return $xactions;
   }
 
-  protected function getObjectLinkButtonLabelForMail() {
+  protected function getObjectLinkButtonLabelForMail(
+    PhabricatorLiskDAO $object) {
     return pht('View Revision');
   }
 
@@ -614,8 +615,7 @@ final class DifferentialTransactionEditor
     $body = id(new PhabricatorMetaMTAMailBody())
       ->setViewer($viewer);
 
-    $revision_uri = $object->getURI();
-    $revision_uri = PhabricatorEnv::getProductionURI($revision_uri);
+    $revision_uri = $this->getObjectLinkButtonURIForMail($object);
     $new_uri = $revision_uri.'/new/';
 
     $this->addHeadersAndCommentsToMailBody(

src/applications/maniphest/editor/ManiphestTransactionEditor.php

@@ -206,7 +206,8 @@ final class ManiphestTransactionEditor
       ->setSubject("T{$id}: {$title}");
   }
 
-  protected function getObjectLinkButtonLabelForMail() {
+  protected function getObjectLinkButtonLabelForMail(
+    PhabricatorLiskDAO $object) {
     return pht('View Task');
   }
 

src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php

@@ -3423,17 +3423,39 @@ abstract class PhabricatorApplicationTransactionEditor
       ->setContextObject($object);
 
     $button_label = $this->getObjectLinkButtonLabelForMail($object);
+    $button_uri = $this->getObjectLinkButtonURIForMail($object);
+
+    $this->addHeadersAndCommentsToMailBody(
+      $body,
+      $xactions,
+      $button_label,
+      $button_uri);
 
-    $this->addHeadersAndCommentsToMailBody($body, $xactions, $button_label);
     $this->addCustomFieldsToMailBody($body, $object, $xactions);
 
     return $body;
   }
 
-  protected function getObjectLinkButtonLabelForMail() {
+  protected function getObjectLinkButtonLabelForMail(
+    PhabricatorLiskDAO $object) {
     return null;
   }
 
+  protected function getObjectLinkButtonURIForMail(
+    PhabricatorLiskDAO $object) {
+
+    // Most objects define a "getURI()" method which does what we want, but
+    // this isn't formally part of an interface at time of writing. Try to
+    // call the method, expecting an exception if it does not exist.
+
+    try {
+      $uri = $object->getURI();
+      return PhabricatorEnv::getProductionURI($uri);
+    } catch (Exception $ex) {
+      return null;
+    }
+  }
+
   /**
    * @task mail
    */
@@ -3455,7 +3477,7 @@ abstract class PhabricatorApplicationTransactionEditor
     PhabricatorMetaMTAMailBody $body,
     array $xactions,
     $object_label = null,
-    $object_href = null) {
+    $object_uri = null) {
 
     // First, remove transactions which shouldn't be rendered in mail.
     foreach ($xactions as $key => $xaction) {
@@ -3521,7 +3543,7 @@ abstract class PhabricatorApplicationTransactionEditor
     $headers_html = phutil_implode_html(phutil_tag('br'), $headers_html);
 
     $header_button = null;
-    if ($object_label !== null) {
+    if ($object_label !== null && $object_uri !== null) {
       $button_style = array(
         'text-decoration: none;',
         'padding: 4px 8px;',
@@ -3540,7 +3562,7 @@ abstract class PhabricatorApplicationTransactionEditor
         'a',
         array(
           'style' => implode(' ', $button_style),
-          'href' => $object_href,
+          'href' => $object_uri,
         ),
         $object_label);
     }