show merged commits in herald emails for merge commits

Summary:
Includes a new Block in Herad emails which tells the user about which commits were merged in a merge commit
Otherwise the email would just say "Merge branch XYZ". Ref T8295

Test Plan: imported various commits (and merges) and watched resulting herald emails for all of them

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8295

Differential Revision: https://secure.phabricator.com/D12993

src/__phutil_library_map__.php

@@ -1541,6 +1541,7 @@ phutil_register_library_map(array(
     'PhabricatorClusterConfigOptions' => 'applications/config/option/PhabricatorClusterConfigOptions.php',
     'PhabricatorCommitBranchesField' => 'applications/repository/customfield/PhabricatorCommitBranchesField.php',
     'PhabricatorCommitCustomField' => 'applications/repository/customfield/PhabricatorCommitCustomField.php',
+    'PhabricatorCommitMergedCommitsField' => 'applications/repository/customfield/PhabricatorCommitMergedCommitsField.php',
     'PhabricatorCommitSearchEngine' => 'applications/audit/query/PhabricatorCommitSearchEngine.php',
     'PhabricatorCommitTagsField' => 'applications/repository/customfield/PhabricatorCommitTagsField.php',
     'PhabricatorCommonPasswords' => 'applications/auth/constants/PhabricatorCommonPasswords.php',
@@ -4906,6 +4907,7 @@ phutil_register_library_map(array(
     'PhabricatorClusterConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorCommitBranchesField' => 'PhabricatorCommitCustomField',
     'PhabricatorCommitCustomField' => 'PhabricatorCustomField',
+    'PhabricatorCommitMergedCommitsField' => 'PhabricatorCommitCustomField',
     'PhabricatorCommitSearchEngine' => 'PhabricatorApplicationSearchEngine',
     'PhabricatorCommitTagsField' => 'PhabricatorCommitCustomField',
     'PhabricatorCommonPasswords' => 'Phobject',

src/applications/diffusion/config/PhabricatorDiffusionConfigOptions.php

@@ -20,6 +20,21 @@ final class PhabricatorDiffusionConfigOptions
   }
 
   public function getOptions() {
+    $custom_field_type = 'custom:PhabricatorCustomFieldConfigOptionType';
+
+    $fields = array(
+      new PhabricatorCommitBranchesField(),
+      new PhabricatorCommitTagsField(),
+      new PhabricatorCommitMergedCommitsField(),
+    );
+
+    $default_fields = array();
+    foreach ($fields as $field) {
+      $default_fields[$field->getFieldKey()] = array(
+        'disabled' => $field->shouldDisableByDefault(),
+      );
+    }
+
     return array(
       $this->newOption(
         'metamta.diffusion.subject-prefix',
@@ -124,6 +139,13 @@ final class PhabricatorDiffusionConfigOptions
             'from web traffic (for example, if you use different SSH and '.
             'web load balancers), you can set the SSH hostname here. This '.
             'is an advanced option.')),
+      $this->newOption('diffusion.fields', $custom_field_type, $default_fields)
+        ->setCustomData(
+          id(new PhabricatorRepositoryCommit())
+          ->getCustomFieldBaseClass())
+        ->setDescription(pht(
+          "Select and reorder diffusion fields.\n\n".
+          "These will primarily show up in Mail Notifications.")),
     );
   }
 

src/applications/repository/customfield/PhabricatorCommitMergedCommitsField.php

@@ -0,0 +1,66 @@
+<?php
+
+final class PhabricatorCommitMergedCommitsField
+  extends PhabricatorCommitCustomField {
+
+  public function getFieldKey() {
+    return 'diffusion:mergedcommits';
+  }
+
+  public function shouldDisableByDefault() {
+    return true;
+  }
+
+  public function shouldAppearInTransactionMail() {
+    return true;
+  }
+
+  public function updateTransactionMailBody(
+    PhabricatorMetaMTAMailBody $body,
+    PhabricatorApplicationTransactionEditor $editor,
+    array $xactions) {
+
+    // Put all the merged commits info int the mail body if this is a merge
+    $merges_caption = '';
+    // TODO: Make this limit configurable after T6030
+    $limit = 50;
+    $commit = $this->getObject();
+
+    try {
+      $merges = DiffusionPathChange::newFromConduit(
+        id(new ConduitCall('diffusion.mergedcommitsquery', array(
+          'commit' => $commit->getCommitIdentifier(),
+          'limit' => $limit + 1,
+          'callsign' => $commit->getRepository()->getCallsign(),
+        )))
+        ->setUser($this->getViewer())
+        ->execute());
+
+      if (count($merges) > $limit) {
+        $merges = array_slice($merges, 0, $limit);
+        $merges_caption =
+          pht("This commit merges more than %d changes. Only the first ".
+          "%d are shown.\n", $limit, $limit);
+      }
+
+      if ($merges) {
+        $merge_commits = array();
+        foreach ($merges as $merge) {
+          $merge_commits[] = $merge->getAuthorName().
+            ': '.
+            $merge->getSummary();
+        }
+        $body->addTextSection(
+          pht('MERGED COMMITS'),
+          $merges_caption.implode("\n", $merge_commits));
+      }
+    } catch (ConduitException $ex) {
+      // Log the exception into the email body
+      $body->addTextSection(
+        pht('MERGED COMMITS'),
+        pht('Error generating merged commits: ').$ex->getMessage());
+    }
+
+  }
+
+}

src/applications/repository/storage/PhabricatorRepositoryCommit.php

@@ -349,9 +349,7 @@ final class PhabricatorRepositoryCommit
 
 
   public function getCustomFieldSpecificationForRole($role) {
-    // TODO: We could make this configurable eventually, but just use the
+    return PhabricatorEnv::getEnvConfig('diffusion.fields');
-    // defaults for now.
-    return array();
   }
 
   public function getCustomFieldBaseClass() {