Improve Diffusion behavior for no-longer-existing commits

Summary:
Ref T9028. When users push a commit, then later delete it (e.g., by deleting the branch which contained it) we currently explode when trying to view it.

Instead, degrade gradually if some information is not available.

Test Plan:
  - Looked at valid commits with parents, refs, branches and merges.
  - Looked at invalid commits.
  - Looked at a previously valid, now-deleted + gc'd commit:

{F859273}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9028

Differential Revision: https://secure.phabricator.com/D14227

src/applications/diffusion/controller/DiffusionCommitController.php

@@ -7,6 +7,12 @@ final class DiffusionCommitController extends DiffusionController {
   private $auditAuthorityPHIDs;
   private $highlightedAudits;
 
+  private $commitParents;
+  private $commitRefs;
+  private $commitMerges;
+  private $commitErrors;
+  private $commitExists;
+
   public function shouldAllowPublic() {
     return true;
   }
@@ -17,6 +23,7 @@ final class DiffusionCommitController extends DiffusionController {
 
   protected function processDiffusionRequest(AphrontRequest $request) {
     $user = $request->getUser();
+
     // This controller doesn't use blob/path stuff, just pass the dictionary
     // in directly instead of using the AphrontRequest parsing mechanism.
     $data = $request->getURIMap();
@@ -45,10 +52,7 @@ final class DiffusionCommitController extends DiffusionController {
     ));
 
     if (!$commit) {
-      $exists = $this->callConduitWithDiffusionRequest(
-        'diffusion.existsquery',
-        array('commit' => $drequest->getCommit()));
-      if (!$exists) {
+      if (!$this->getCommitExists()) {
         return new Aphront404Response();
       }
 
@@ -95,18 +99,6 @@ final class DiffusionCommitController extends DiffusionController {
 
       require_celerity_resource('phabricator-remarkup-css');
 
-      $parents = $this->callConduitWithDiffusionRequest(
-        'diffusion.commitparentsquery',
-        array('commit' => $drequest->getCommit()));
-
-      if ($parents) {
-        $parents = id(new DiffusionCommitQuery())
-          ->setViewer($user)
-          ->withRepository($repository)
-          ->withIdentifiers($parents)
-          ->execute();
-      }
-
       $headsup_view = id(new PHUIHeaderView())
         ->setHeader(nonempty($commit->getSummary(), pht('Commit Detail')));
 
@@ -115,7 +107,6 @@ final class DiffusionCommitController extends DiffusionController {
       $commit_properties = $this->loadCommitProperties(
         $commit,
         $commit_data,
-        $parents,
         $audit_requests);
       $property_list = id(new PHUIPropertyListView())
         ->setHasKeyboardShortcuts(true)
@@ -148,8 +139,10 @@ final class DiffusionCommitController extends DiffusionController {
           $message));
 
       $headsup_view->setTall(true);
+
       $object_box = id(new PHUIObjectBoxView())
         ->setHeader($headsup_view)
+        ->setFormErrors($this->getCommitErrors())
         ->addPropertyList($property_list)
         ->addPropertyList($detail_list);
 
@@ -216,6 +209,10 @@ final class DiffusionCommitController extends DiffusionController {
           'This commit is enormous, and affects more than %d files. '.
           'Changes are not shown.',
           $hard_limit));
+    } else if (!$this->getCommitExists()) {
+      $content[] = $this->renderStatusMessage(
+        pht('Commit No Longer Exists'),
+        pht('This commit no longer exists in the repository.'));
     } else {
       $show_changesets = true;
 
@@ -382,10 +379,8 @@ final class DiffusionCommitController extends DiffusionController {
   private function loadCommitProperties(
     PhabricatorRepositoryCommit $commit,
     PhabricatorRepositoryCommitData $data,
-    array $parents,
     array $audit_requests) {
 
-    assert_instances_of($parents, 'PhabricatorRepositoryCommit');
     $viewer = $this->getRequest()->getUser();
     $commit_phid = $commit->getPHID();
     $drequest = $this->getDiffusionRequest();
@@ -423,11 +418,6 @@ final class DiffusionCommitController extends DiffusionController {
     if ($data->getCommitDetail('committerPHID')) {
       $phids[] = $data->getCommitDetail('committerPHID');
     }
-    if ($parents) {
-      foreach ($parents as $parent) {
-        $phids[] = $parent->getPHID();
-      }
-    }
 
     // NOTE: We should never normally have more than a single push log, but
     // it can occur naturally if a commit is pushed, then the branch it was
@@ -564,14 +554,12 @@ final class DiffusionCommitController extends DiffusionController {
       $props['Differential Revision'] = $handles[$revision_phid]->renderLink();
     }
 
+    $parents = $this->getCommitParents();
     if ($parents) {
-      $parent_links = array();
-      foreach ($parents as $parent) {
-        $parent_links[] = $handles[$parent->getPHID()]->renderLink();
-      }
-      $props['Parents'] = phutil_implode_html(" \xC2\xB7 ", $parent_links);
+      $props['Parents'] = $viewer->renderHandleList(mpull($parents, 'getPHID'));
     }
 
+    if ($this->getCommitExists()) {
       $props['Branches'] = phutil_tag(
         'span',
         array(
@@ -593,10 +581,20 @@ final class DiffusionCommitController extends DiffusionController {
           $root.'/branches/' => 'commit-branches',
           $root.'/tags/' => 'commit-tags',
         ));
+    }
 
-    $refs = $this->buildRefs($drequest);
+    $refs = $this->getCommitRefs();
     if ($refs) {
-      $props['References'] = $refs;
+      $ref_links = array();
+      foreach ($refs as $ref_data) {
+        $ref_links[] = phutil_tag(
+          'a',
+          array(
+            'href' => $ref_data['href'],
+          ),
+          $ref_data['ref']);
+      }
+      $props['References'] = phutil_implode_html(', ', $ref_links);
     }
 
     if ($reverts_phids) {
@@ -860,26 +858,12 @@ final class DiffusionCommitController extends DiffusionController {
     $drequest = $this->getDiffusionRequest();
     $repository = $drequest->getRepository();
 
-    $vcs = $repository->getVersionControlSystem();
-    switch ($vcs) {
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
-        // These aren't supported under SVN.
-        return null;
-    }
-
-    $limit = 50;
-
-    $merges = $this->callConduitWithDiffusionRequest(
-      'diffusion.mergedcommitsquery',
-      array(
-        'commit' => $drequest->getCommit(),
-        'limit' => $limit + 1,
-      ));
-
+    $merges = $this->getCommitMerges();
     if (!$merges) {
       return null;
     }
-    $merges = DiffusionPathChange::newFromConduit($merges);
+
+    $limit = $this->getMergeDisplayLimit();
 
     $caption = null;
     if (count($merges) > $limit) {
@@ -961,27 +945,6 @@ final class DiffusionCommitController extends DiffusionController {
     return $actions;
   }
 
-  private function buildRefs(DiffusionRequest $request) {
-    // this is git-only, so save a conduit round trip and just get out of
-    // here if the repository isn't git
-    $type_git = PhabricatorRepositoryType::REPOSITORY_TYPE_GIT;
-    $repository = $request->getRepository();
-    if ($repository->getVersionControlSystem() != $type_git) {
-      return null;
-    }
-
-    $results = $this->callConduitWithDiffusionRequest(
-      'diffusion.refsquery',
-      array('commit' => $request->getCommit()));
-    $ref_links = array();
-    foreach ($results as $ref_data) {
-      $ref_links[] = phutil_tag('a',
-        array('href' => $ref_data['href']),
-        $ref_data['ref']);
-    }
-    return phutil_implode_html(', ', $ref_links);
-  }
-
   private function buildRawDiffResponse(DiffusionRequest $drequest) {
     $raw_diff = $this->callConduitWithDiffusionRequest(
       'diffusion.rawdiffquery',
@@ -1137,4 +1100,140 @@ final class DiffusionCommitController extends DiffusionController {
     return $toc_view;
   }
 
+  private function loadCommitState() {
+    $viewer = $this->getViewer();
+    $drequest = $this->getDiffusionRequest();
+    $repository = $drequest->getRepository();
+    $commit = $drequest->getCommit();
+
+    // TODO: We could use futures here and resolve these calls in parallel.
+
+    $exceptions = array();
+
+    try {
+      $parent_refs = $this->callConduitWithDiffusionRequest(
+        'diffusion.commitparentsquery',
+        array(
+          'commit' => $commit,
+        ));
+
+      if ($parent_refs) {
+        $parents = id(new DiffusionCommitQuery())
+          ->setViewer($viewer)
+          ->withRepository($repository)
+          ->withIdentifiers($parent_refs)
+          ->execute();
+      } else {
+        $parents = array();
+      }
+
+      $this->commitParents = $parents;
+    } catch (Exception $ex) {
+      $this->commitParents = false;
+      $exceptions[] = $ex;
+    }
+
+    $merge_limit = $this->getMergeDisplayLimit();
+
+    try {
+      $merges = $this->callConduitWithDiffusionRequest(
+        'diffusion.mergedcommitsquery',
+        array(
+          'commit' => $commit,
+          'limit' => $merge_limit + 1,
+        ));
+
+      $this->commitMerges = DiffusionPathChange::newFromConduit($merges);
+    } catch (Exception $ex) {
+      $this->commitMerges = false;
+      $exceptions[] = $ex;
+    }
+
+
+    try {
+      if ($repository->isGit()) {
+        $refs = $this->callConduitWithDiffusionRequest(
+          'diffusion.refsquery',
+          array(
+            'commit' => $commit,
+          ));
+      } else {
+        $refs = array();
+      }
+
+      $this->commitRefs = $refs;
+    } catch (Exception $ex) {
+      $this->commitRefs = false;
+      $exceptions[] = $ex;
+    }
+
+    if ($exceptions) {
+      $exists = $this->callConduitWithDiffusionRequest(
+        'diffusion.existsquery',
+        array(
+          'commit' => $commit,
+        ));
+
+      if ($exists) {
+        $this->commitExists = true;
+        foreach ($exceptions as $exception) {
+          $this->commitErrors[] = $exception->getMessage();
+        }
+      } else {
+        $this->commitExists = false;
+        $this->commitErrors[] = pht(
+          'This commit no longer exists in the repository. It may have '.
+          'been part of a branch which was deleted.');
+      }
+    } else {
+      $this->commitExists = true;
+      $this->commitErrors = array();
+    }
+  }
+
+  private function getMergeDisplayLimit() {
+    return 50;
+  }
+
+  private function getCommitExists() {
+    if ($this->commitExists === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitExists;
+  }
+
+  private function getCommitParents() {
+    if ($this->commitParents === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitParents;
+  }
+
+  private function getCommitRefs() {
+    if ($this->commitRefs === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitRefs;
+  }
+
+  private function getCommitMerges() {
+    if ($this->commitMerges === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitMerges;
+  }
+
+  private function getCommitErrors() {
+    if ($this->commitErrors === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitErrors;
+  }
+
+
 }