Don't return any results for viewerprojects() if the viewer is in no projects

Summary:
Fixes T10135. When the viewer is a member of no projects, specify the constraint type as a new "EMPTY" type.

When a query has an "EMPTY" constraint, fail fast with no results.

Test Plan:
  - Viewed a viewerprojects() query result set as a user in no projects.
    - Before patch: got a lot of hits. After patch: no hits.
  - Viewed a normal result set, no changes.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10135

Differential Revision: https://secure.phabricator.com/D15003

src/applications/project/typeahead/PhabricatorProjectLogicalViewerDatasource.php

@@ -63,11 +63,17 @@ final class PhabricatorProjectLogicalViewerDatasource
     $phids = mpull($projects, 'getPHID');
 
     $results = array();
+    if ($phids) {
       foreach ($phids as $phid) {
         $results[] = new PhabricatorQueryConstraint(
           PhabricatorQueryConstraint::OPERATOR_OR,
           $phid);
       }
+    } else {
+      $results[] = new PhabricatorQueryConstraint(
+        PhabricatorQueryConstraint::OPERATOR_EMPTY,
+        null);
+    }
 
     return $results;
   }

src/infrastructure/query/constraint/PhabricatorQueryConstraint.php

@@ -7,6 +7,7 @@ final class PhabricatorQueryConstraint extends Phobject {
   const OPERATOR_NOT = 'not';
   const OPERATOR_NULL = 'null';
   const OPERATOR_ANCESTOR = 'ancestor';
+  const OPERATOR_EMPTY = 'empty';
 
   private $operator;
   private $value;

src/infrastructure/query/policy/PhabricatorCursorPagedPolicyAwareQuery.php

@@ -1872,6 +1872,16 @@ abstract class PhabricatorCursorPagedPolicyAwareQuery
       return $this;
     }
 
+    foreach ($this->edgeLogicConstraints as $type => $constraints) {
+      foreach ($constraints as $operator => $list) {
+        switch ($operator) {
+          case PhabricatorQueryConstraint::OPERATOR_EMPTY:
+            throw new PhabricatorEmptyQueryException(
+              pht('This query specifies an empty constraint.'));
+        }
+      }
+    }
+
     // This should probably be more modular, eventually, but we only do
     // project-based edge logic today.