Phabricator Diffusion: handle missing path errors in browse view

Summary:
When the user gets a path wrong, show them a helpful error message, as
in Diffusion/Confusion.

Test Plan:
Browsed some nonexistent and previously-deleted paths.

Reviewed By: aran
Reviewers: aran, jwilson
CC: aran
Differential Revision: 59

src/applications/diffusion/controller/browse/DiffusionBrowseController.php

@@ -42,10 +42,43 @@ class DiffusionBrowseController extends DiffusionController {
       $this->commit);
     $results = $browse_data->loadPaths();
 
+    $content = array();
+
     if (!$results) {
-      // TODO: useful output (path does not exist / never existed), or file
-      // data.
-      throw new Exception("No browse results.");
+
+      switch ($browse_data->getReasonForEmptyResultSet()) {
+        case DiffusionBrowseQuery::REASON_IS_NONEXISTENT:
+          $title = 'Path Does Not Exist';
+          // TODO: Under git, this error message should be more specific. It
+          // may exist on some other branch.
+          $body  = "This path does not exist anywhere.";
+          $severity = AphrontErrorView::SEVERITY_ERROR;
+          break;
+        case DiffusionBrowseQuery::REASON_IS_DELETED:
+          // TODO: Format all these commits into nice VCS-agnostic links.
+          $commit = $this->commit;
+          $deleted = $browse_data->getDeletedAtCommit();
+          $existed = $browse_data->getExistedAtCommit();
+
+          $title = 'Path Was Deleted';
+          $body = "This path does not exist at {$commit}. It was deleted in ".
+                  "{$deleted} and last existed at {$existed}.";
+          $severity = AphrontErrorView::SEVERITY_WARNING;
+          break;
+        case DiffusionBrowseQuery::REASON_IS_FILE:
+          throw new Exception("TODO: implement this");
+          break;
+        default:
+          throw new Exception("Unknown failure reason!");
+      }
+
+      $error_view = new AphrontErrorView();
+      $error_view->setSeverity($severity);
+      $error_view->setTitle($title);
+      $error_view->appendChild('<p>'.$body.'</p>');
+
+      $content[] = $error_view;
+
     } else {
       $browse_table = new DiffusionBrowseTableView();
       $browse_table->setRepository($repository);
@@ -57,6 +90,8 @@ class DiffusionBrowseController extends DiffusionController {
       $browse_panel->setHeader($this->path);
       $browse_panel->appendChild($browse_table);
 
+      $content[] = $browse_panel;
+
       // TODO: Branch table
     }
 
@@ -64,7 +99,7 @@ class DiffusionBrowseController extends DiffusionController {
     // TODO: Side nav
 
     return $this->buildStandardPageResponse(
-      $browse_panel,
+      $content,
       array(
         'title' => basename($this->path),
       ));

src/applications/diffusion/controller/browse/__init__.php

@@ -9,6 +9,7 @@
 phutil_require_module('phabricator', 'applications/diffusion/controller/base');
 phutil_require_module('phabricator', 'applications/diffusion/query/browse/base');
 phutil_require_module('phabricator', 'applications/diffusion/view/browsetable');
+phutil_require_module('phabricator', 'view/form/error');
 phutil_require_module('phabricator', 'view/layout/panel');
 
 phutil_require_module('phutil', 'utils');

src/applications/diffusion/query/browse/base/DiffusionBrowseQuery.php

@@ -23,9 +23,12 @@ abstract class DiffusionBrowseQuery {
   private $commit;
 
   protected $reason;
+  protected $existedAtCommit;
+  protected $deletedAtCommit;
 
-  const REASON_IS_FILE          = 'is-file';
-  const REASON_IS_NONEXISTENT   = 'nonexistent';
+  const REASON_IS_FILE            = 'is-file';
+  const REASON_IS_DELETED         = 'is-deleted';
+  const REASON_IS_NONEXISTENT     = 'nonexistent';
 
   final private function __construct() {
     // <private>
@@ -71,6 +74,14 @@ abstract class DiffusionBrowseQuery {
     return $this->reason;
   }
 
+  final public function getExistedAtCommit() {
+    return $this->existedAtCommit;
+  }
+
+  final public function getDeletedAtCommit() {
+    return $this->deletedAtCommit;
+  }
+
   final public function loadPaths() {
     return $this->executeQuery();
   }

src/applications/diffusion/query/browse/git/DiffusionGitBrowseQuery.php

@@ -36,6 +36,22 @@ final class DiffusionGitBrowseQuery extends DiffusionBrowseQuery {
         $path);
     } catch (CommandException $e) {
       if (preg_match('/^fatal: Not a valid object name/', $e->getStderr())) {
+        // Grab two logs, since the first one is when the object was deleted.
+        list($stdout) = execx(
+          '(cd %s && %s log -n2 --format="%%H" %s -- %s)',
+          $local_path,
+          $git,
+          $commit,
+          $path);
+        $stdout = trim($stdout);
+        if ($stdout) {
+          $commits = explode("\n", $stdout);
+          $this->reason = self::REASON_IS_DELETED;
+          $this->deletedAtCommit = idx($commits, 0);
+          $this->existedAtCommit = idx($commits, 1);
+          return array();
+        }
+
         $this->reason = self::REASON_IS_NONEXISTENT;
         return array();
       } else {