Show login page if a search token requires a valid viewer

Summary:
A saved query can have tokens that require a valid current viewer. For example, this token:

    viewer()

Before this change, visiting such saved queries would cause this:

    This datasource ("PhabricatorPeopleUserFunctionDatasource") can not evaluate the function "viewer(...)".

After this change, instead of that, you are just redirected to the login page,
so, after you do the login, you are redirected back to that saved query and it works.

This fix was boosted during the Wikimedia Hackaton (wmhack) in Tallinn. Thanks Tallinn!

https://phabricator.wikimedia.org/T356384

Fixes T15704

Test Plan:
Go to Maniphest > Advanced Search > Assigned to > "Viewer". It still works.

Visit the same page in a new anonymous tab: now it redirects to the login page. You login,
and that page works again.

Do the same specific test for all these cases:

- Maniphest
    - Assigned To: viewer
    - Tags: current Viewer's Projects
    - Authors: viewer
    - Subscribers: ...
    - Closed by
- Badges
    - Subscribers
- Differential
    - Responsible Users
    - Authors
    - Reviewers
    - Subscribers
    - Tags
- Dashboards
    - Authored By
    - Tags
- Dashboard Panels
    - Authored By
- Dashboard Portals
    - Tags
- Calendar:
    - Hosts
    - Invited
    - Subscribers
    - Tags
- Countdown
    - Authors
- Diffusion
    - Tags
    - Subscribers
    - Tags
- Diffusion commit
    - Responsible Users
    - Authors
    - Subscribers
    - Tags
- Diffusion identities
    - Matching Users
- Feed
    - Include Users
    - Include Projects (interestingly it does not support "current Viewer's Projects")
- Files
    - Authors
- Herald
    - Authors
    - Subscribers
- Legalpad
    - Subscribers
- Nuance (none of their entity support search by token)
- Passphrase
    - Subscribers
- Paste
    - Authors
    - Subscribers
    - Tags
- Phame
    - Subscribers
    - Tags
- Pholio
    - Authors
    - Subscribers
    - Tags
- Phrequent
    - Users (interestingly it does not support "viewer")
- Ponder
    - Authors
    - Answered By
- Projects
    - Members
    - Watchers
- Transactions - /feed/transactions/
    - Authors
- General search at /search/query/
    - Authors
    - Owners
    - Subscribers
    - Tags

All the above fields were tested in a clean search, one at a time, both logged-in and logged-out, with the function "viewer" or anything similar like "current Viewer's Projects":

For all cases, the login page appeared successfully where needed, instead of a crash.

Reviewers: O1 Blessed Committers, aklapper

Reviewed By: O1 Blessed Committers, aklapper

Subscribers: aklapper, avivey, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15704

Differential Revision: https://we.phorge.it/D25621

src/__phutil_library_map__.php

@@ -5078,6 +5078,7 @@ phutil_register_library_map(array(
     'PhabricatorTypeaheadDatasourceTestCase' => 'applications/typeahead/datasource/__tests__/PhabricatorTypeaheadDatasourceTestCase.php',
     'PhabricatorTypeaheadFunctionHelpController' => 'applications/typeahead/controller/PhabricatorTypeaheadFunctionHelpController.php',
     'PhabricatorTypeaheadInvalidTokenException' => 'applications/typeahead/exception/PhabricatorTypeaheadInvalidTokenException.php',
+    'PhabricatorTypeaheadLoginRequiredException' => 'applications/typeahead/exception/PhabricatorTypeaheadLoginRequiredException.php',
     'PhabricatorTypeaheadModularDatasourceController' => 'applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php',
     'PhabricatorTypeaheadMonogramDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadMonogramDatasource.php',
     'PhabricatorTypeaheadProxyDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadProxyDatasource.php',
@@ -11819,6 +11820,7 @@ phutil_register_library_map(array(
     'PhabricatorTypeaheadDatasourceTestCase' => 'PhabricatorTestCase',
     'PhabricatorTypeaheadFunctionHelpController' => 'PhabricatorTypeaheadDatasourceController',
     'PhabricatorTypeaheadInvalidTokenException' => 'Exception',
+    'PhabricatorTypeaheadLoginRequiredException' => 'Exception',
     'PhabricatorTypeaheadModularDatasourceController' => 'PhabricatorTypeaheadDatasourceController',
     'PhabricatorTypeaheadMonogramDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorTypeaheadProxyDatasource' => 'PhabricatorTypeaheadCompositeDatasource',

src/applications/calendar/typeahead/PhabricatorCalendarInviteeViewerFunctionDatasource.php

@@ -28,8 +28,12 @@ final class PhabricatorCalendarInviteeViewerFunctionDatasource
     );
   }
 
+  protected function isFunctionWithLoginRequired($function) {
+    return true;
+  }
+
   public function loadResults() {
-    if ($this->getViewer()->getPHID()) {
+    if ($this->getViewer()->isLoggedIn()) {
       $results = array($this->renderViewerFunctionToken());
     } else {
       $results = array();
@@ -39,7 +43,7 @@ final class PhabricatorCalendarInviteeViewerFunctionDatasource
   }
 
   protected function canEvaluateFunction($function) {
-    if (!$this->getViewer()->getPHID()) {
+    if (!$this->getViewer()->isLoggedIn()) {
       return false;
     }
 

src/applications/differential/typeahead/DifferentialResponsibleViewerFunctionDatasource.php

@@ -28,8 +28,12 @@ final class DifferentialResponsibleViewerFunctionDatasource
     );
   }
 
+  protected function isFunctionWithLoginRequired($function) {
+    return true;
+  }
+
   public function loadResults() {
-    if ($this->getViewer()->getPHID()) {
+    if ($this->getViewer()->isLoggedIn()) {
       $results = array($this->renderViewerFunctionToken());
     } else {
       $results = array();
@@ -39,7 +43,7 @@ final class DifferentialResponsibleViewerFunctionDatasource
   }
 
   protected function canEvaluateFunction($function) {
-    if (!$this->getViewer()->getPHID()) {
+    if (!$this->getViewer()->isLoggedIn()) {
       return false;
     }
 

src/applications/people/typeahead/PhabricatorViewerDatasource.php

@@ -34,8 +34,12 @@ final class PhabricatorViewerDatasource
     );
   }
 
+  protected function isFunctionWithLoginRequired($function) {
+    return true;
+  }
+
   public function loadResults() {
-    if ($this->getViewer()->getPHID()) {
+    if ($this->getViewer()->isLoggedIn()) {
       $results = array($this->renderViewerFunctionToken());
     } else {
       $results = array();
@@ -45,7 +49,7 @@ final class PhabricatorViewerDatasource
   }
 
   protected function canEvaluateFunction($function) {
-    if (!$this->getViewer()->getPHID()) {
+    if (!$this->getViewer()->isLoggedIn()) {
       return false;
     }
 

src/applications/project/typeahead/PhabricatorProjectLogicalViewerDatasource.php

@@ -35,8 +35,12 @@ final class PhabricatorProjectLogicalViewerDatasource
     );
   }
 
+  protected function isFunctionWithLoginRequired($function) {
+    return true;
+  }
+
   public function loadResults() {
-    if ($this->getViewer()->getPHID()) {
+    if ($this->getViewer()->isLoggedIn()) {
       $results = array($this->renderViewerProjectsFunctionToken());
     } else {
       $results = array();
@@ -46,7 +50,7 @@ final class PhabricatorProjectLogicalViewerDatasource
   }
 
   protected function canEvaluateFunction($function) {
-    if (!$this->getViewer()->getPHID()) {
+    if (!$this->getViewer()->isLoggedIn()) {
       return false;
     }
 

src/applications/search/controller/PhabricatorApplicationSearchController.php

@@ -346,6 +346,15 @@ final class PhabricatorApplicationSearchController
             $body[] = $pager_box;
           }
         }
+      } catch (PhabricatorTypeaheadLoginRequiredException $ex) {
+
+        // A specific token requires login. Show login page.
+        $auth_class = PhabricatorAuthApplication::class;
+        $auth_application = PhabricatorApplication::getByClass($auth_class);
+        $login_controller = new PhabricatorAuthStartController();
+        $this->setCurrentApplication($auth_application);
+        return $this->delegateToController($login_controller);
+
       } catch (PhabricatorTypeaheadInvalidTokenException $ex) {
         $exec_errors[] = pht(
           'This query specifies an invalid parameter. Review the '.

src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php

@@ -304,6 +304,15 @@ abstract class PhabricatorTypeaheadCompositeDatasource
     return parent::evaluateFunction($function, $argv);
   }
 
+  protected function isFunctionWithLoginRequired($function) {
+    foreach ($this->getUsableDatasources() as $source) {
+      if ($source->isFunctionWithLoginRequired($function)) {
+        return true;
+      }
+    }
+    return parent::isFunctionWithLoginRequired($function);
+  }
+
   public function renderFunctionTokens($function, array $argv_list) {
     foreach ($this->getUsableDatasources() as $source) {
       if ($source->canEvaluateFunction($function)) {

src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php

@@ -365,6 +365,19 @@ abstract class PhabricatorTypeaheadDatasource extends Phobject {
   }
 
 
+  /**
+   * Check if this datasource requires a logged-in viewer.
+   * @task functions
+   * @param string $function Function name.
+   * @return bool
+   */
+  protected function isFunctionWithLoginRequired($function) {
+    // This is just a default.
+    // Make sure to override this method to require login.
+    return false;
+  }
+
+
   /**
    * @task functions
    */
@@ -498,6 +511,18 @@ abstract class PhabricatorTypeaheadDatasource extends Phobject {
 
     if (!$this->canEvaluateFunction($function)) {
       if (!$allow_partial) {
+
+        if ($this->isFunctionWithLoginRequired($function)) {
+          if (!$this->getViewer() || !$this->getViewer()->isLoggedIn()) {
+            throw new PhabricatorTypeaheadLoginRequiredException(
+              pht(
+                'This datasource ("%s") requires to be logged-in to use the '.
+                'function "%s(...)".',
+                get_class($this),
+                $function));
+          }
+        }
+
         throw new PhabricatorTypeaheadInvalidTokenException(
           pht(
             'This datasource ("%s") can not evaluate the function "%s(...)".',

src/applications/typeahead/exception/PhabricatorTypeaheadLoginRequiredException.php

@@ -0,0 +1,6 @@
+<?php
+
+/**
+ * Exception thrown when a specific typehead requires login to be used.
+ */
+final class PhabricatorTypeaheadLoginRequiredException extends Exception {}