diff --git a/.zuul.yaml b/.zuul.yaml
index 27c8491..52c12ce 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -2,7 +2,8 @@
     name: plugins-task-build
     parent: gerrit-plugin-build
     pre-run:
-        tools/playbooks/install_docker.yaml
+        - tools/playbooks/install_docker.yaml
+        - tools/playbooks/install_python3-distutils.yaml
     vars:
         bazelisk_test_targets: "plugins/task/lint_test plugins/task/..."
 
diff --git a/gr-task-plugin/gr-task-plugin.js b/gr-task-plugin/gr-task-plugin.js
index 34fa467..7e1add6 100644
--- a/gr-task-plugin/gr-task-plugin.js
+++ b/gr-task-plugin/gr-task-plugin.js
@@ -127,7 +127,7 @@
         icon.tooltip = 'Failed';
         break;
       case 'READY':
-        icon.id = 'gr-icons:rebase';
+        icon.id = 'gr-icons:playArrow';
         icon.color = 'green';
         icon.tooltip = 'Ready';
         break;
@@ -137,13 +137,18 @@
         icon.tooltip = 'Invalid';
         break;
       case 'WAITING':
-        icon.id = 'gr-icons:side-by-side';
+        icon.id = 'gr-icons:pause';
         icon.color = 'red';
         icon.tooltip = 'Waiting';
         break;
-      case 'PASS':
+      case 'DUPLICATE':
         icon.id = 'gr-icons:check';
         icon.color = 'green';
+        icon.tooltip = 'Duplicate';
+        break;
+      case 'PASS':
+        icon.id = 'gr-icons:check-circle';
+        icon.color = 'green';
         icon.tooltip = 'Passed';
         break;
     }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/Copier.java b/src/main/java/com/googlesource/gerrit/plugins/task/Copier.java
index 2c0ccad..10f4048 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/Copier.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/Copier.java
@@ -14,44 +14,19 @@
 
 package com.googlesource.gerrit.plugins.task;
 
-import com.google.common.primitives.Primitives;
 import java.lang.reflect.Field;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
 
 public class Copier {
-  protected static <T> void deepCopyDeclaredFields(
-      Class<T> cls,
-      T from,
-      T to,
-      boolean includeInaccessible,
-      Collection<Class<?>> copyReferenceOnly) {
+  protected static <T> void shallowCopyDeclaredFields(
+      Class<T> cls, T from, T to, boolean includeInaccessible) {
     for (Field field : cls.getDeclaredFields()) {
       try {
         if (includeInaccessible) {
           field.setAccessible(true);
         }
-        Class<?> fieldCls = field.getType();
         Object val = field.get(from);
-        if (field.getType().isPrimitive()
-            || Primitives.isWrapperType(fieldCls)
-            || (val instanceof String)
-            || val == null
-            || copyReferenceOnly.contains(fieldCls)) {
+        if (!field.getName().equals("this$0")) { // Can't copy internal final field
           field.set(to, val);
-        } else if (val instanceof List) {
-          List<?> list = List.class.cast(val);
-          field.set(to, new ArrayList<>(list));
-        } else if (val instanceof Map) {
-          Map<?, ?> map = Map.class.cast(val);
-          field.set(to, new HashMap<>(map));
-        } else if (field.getName().equals("this$0")) { // Can't copy internal final field
-        } else {
-          throw new RuntimeException(
-              "Don't know how to deep copy " + fieldValueToString(field, val));
         }
       } catch (IllegalAccessException e) {
         if (includeInaccessible) {
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/CopyOnWrite.java b/src/main/java/com/googlesource/gerrit/plugins/task/CopyOnWrite.java
index efafd57..8369d67 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/CopyOnWrite.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/CopyOnWrite.java
@@ -14,9 +14,58 @@
 
 package com.googlesource.gerrit.plugins.task;
 
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.Optional;
 import java.util.function.Function;
 
 public class CopyOnWrite<T> {
+  public static class CloneOnWrite<C extends Cloneable> extends CopyOnWrite<C> {
+    public CloneOnWrite(C cloneable) {
+      super(cloneable, copier(cloneable));
+    }
+  }
+
+  public static <C extends Cloneable> Function<C, C> copier(C cloneable) {
+    return c -> clone(c);
+  }
+
+  @SuppressWarnings("unchecked")
+  public static <C extends Cloneable> C clone(C cloneable) {
+    try {
+      for (Class<?> cls = cloneable.getClass(); cls != null; cls = cls.getSuperclass()) {
+        Optional<Method> optional = getOptionalDeclaredMethod(cls, "clone");
+        if (optional.isPresent()) {
+          Method clone = optional.get();
+          clone.setAccessible(true);
+          return (C) cloneable.getClass().cast(clone.invoke(cloneable));
+        }
+      }
+      throw new RuntimeException("Cannot find clone() method");
+    } catch (SecurityException
+        | IllegalAccessException
+        | IllegalArgumentException
+        | InvocationTargetException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /**
+   * A faster getDeclaredMethod() without exceptions. The original apparently does a linear search
+   * anyway, and it is significantly slower when it throws NoSuchMethodExceptions.
+   */
+  public static Optional<Method> getOptionalDeclaredMethod(
+      Class<?> cls, String name, Class<?>... parameterTypes) {
+    for (Method method : cls.getDeclaredMethods()) {
+      if (method.getName().equals(name)
+          && Arrays.equals(method.getParameterTypes(), parameterTypes)) {
+        return Optional.of(method);
+      }
+    }
+    return Optional.empty();
+  }
+
   protected Function<T, T> copier;
   protected T original;
   protected T copy;
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/MatchCache.java b/src/main/java/com/googlesource/gerrit/plugins/task/MatchCache.java
index 45fe46d..ef5af15 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/MatchCache.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/MatchCache.java
@@ -31,25 +31,28 @@
     this.changeData = changeData;
   }
 
-  protected boolean match(String query) throws StorageException, QueryParseException {
+  public boolean match(String query) throws StorageException, QueryParseException {
     if (query == null) {
       return true;
     }
     Boolean isMatched = matchResultByQuery.get(query);
     if (isMatched == null) {
-      isMatched = predicateCache.match(changeData, query);
+      isMatched = predicateCache.matchWithExceptions(changeData, query);
       matchResultByQuery.put(query, isMatched);
     }
     return isMatched;
   }
 
-  protected Boolean matchOrNull(String query) {
+  public Boolean matchOrNull(String query) {
     if (query == null) {
       return null;
     }
     Boolean isMatched = matchResultByQuery.get(query);
     if (isMatched == null) {
-      isMatched = predicateCache.matchOrNull(changeData, query);
+      try {
+        isMatched = predicateCache.matchWithExceptions(changeData, query);
+      } catch (QueryParseException | RuntimeException e) {
+      }
       matchResultByQuery.put(query, isMatched);
     }
     return isMatched;
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/PredicateCache.java b/src/main/java/com/googlesource/gerrit/plugins/task/PredicateCache.java
index 7896417..6540ad2 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/PredicateCache.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/PredicateCache.java
@@ -15,46 +15,52 @@
 package com.googlesource.gerrit.plugins.task;
 
 import com.google.gerrit.exceptions.StorageException;
+import com.google.gerrit.extensions.annotations.PluginName;
+import com.google.gerrit.index.query.AndPredicate;
+import com.google.gerrit.index.query.NotPredicate;
+import com.google.gerrit.index.query.OrPredicate;
 import com.google.gerrit.index.query.Predicate;
 import com.google.gerrit.index.query.QueryParseException;
 import com.google.gerrit.server.CurrentUser;
+import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.gerrit.server.query.change.ChangeQueryBuilder;
+import com.google.gerrit.server.query.change.DestinationPredicate;
+import com.google.gerrit.server.query.change.ProjectPredicate;
+import com.google.gerrit.server.query.change.RefPredicate;
+import com.google.gerrit.server.query.change.RegexProjectPredicate;
+import com.google.gerrit.server.query.change.RegexRefPredicate;
 import com.google.inject.Inject;
+import java.util.Arrays;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
+import java.util.Set;
+import org.eclipse.jgit.lib.Config;
 
 public class PredicateCache {
   protected final ChangeQueryBuilder cqb;
+  protected final Set<String> cacheableByBranchPredicateClassNames;
   protected final CurrentUser user;
 
   protected final Map<String, ThrowingProvider<Predicate<ChangeData>, QueryParseException>>
       predicatesByQuery = new HashMap<>();
 
   @Inject
-  public PredicateCache(CurrentUser user, ChangeQueryBuilder cqb) {
+  public PredicateCache(
+      @GerritServerConfig Config config,
+      @PluginName String pluginName,
+      CurrentUser user,
+      ChangeQueryBuilder cqb) {
     this.user = user;
     this.cqb = cqb;
+    cacheableByBranchPredicateClassNames =
+        new HashSet<>(
+            Arrays.asList(
+                config.getStringList(pluginName, "cacheable-predicates", "byBranch-className")));
   }
 
-  public boolean match(ChangeData c, String query) throws StorageException, QueryParseException {
-    if (query == null) {
-      return true;
-    }
-    return matchWithExceptions(c, query);
-  }
-
-  public Boolean matchOrNull(ChangeData c, String query) {
-    if (query != null) {
-      try {
-        return matchWithExceptions(c, query);
-      } catch (QueryParseException | RuntimeException e) {
-      }
-    }
-    return null;
-  }
-
-  protected boolean matchWithExceptions(ChangeData c, String query)
+  public boolean matchWithExceptions(ChangeData c, String query)
       throws QueryParseException, StorageException {
     if ("true".equalsIgnoreCase(query)) {
       return true;
@@ -78,4 +84,39 @@
       throw e;
     }
   }
+
+  /**
+   * Can this query's output be assumed to be constant given any Change destined for the same
+   * Branch.NameKey?
+   */
+  public boolean isCacheableByBranch(String query) throws QueryParseException {
+    if (query == null
+        || "".equals(query)
+        || "false".equalsIgnoreCase(query)
+        || "true".equalsIgnoreCase(query)) {
+      return true;
+    }
+    return isCacheableByBranch(getPredicate(query));
+  }
+
+  protected boolean isCacheableByBranch(Predicate<ChangeData> predicate) {
+    if (predicate instanceof AndPredicate
+        || predicate instanceof NotPredicate
+        || predicate instanceof OrPredicate) {
+      for (Predicate<ChangeData> subPred : predicate.getChildren()) {
+        if (!isCacheableByBranch(subPred)) {
+          return false;
+        }
+      }
+      return true;
+    }
+    if (predicate instanceof DestinationPredicate
+        || predicate instanceof ProjectPredicate
+        || predicate instanceof RefPredicate
+        || predicate instanceof RegexProjectPredicate
+        || predicate instanceof RegexRefPredicate) {
+      return true;
+    }
+    return cacheableByBranchPredicateClassNames.contains(predicate.getClass().getName());
+  }
 }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/Preloader.java b/src/main/java/com/googlesource/gerrit/plugins/task/Preloader.java
index c48ed6e..b240c3b 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/Preloader.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/Preloader.java
@@ -14,7 +14,10 @@
 
 package com.googlesource.gerrit.plugins.task;
 
+import com.google.inject.Inject;
 import com.googlesource.gerrit.plugins.task.TaskConfig.Task;
+import com.googlesource.gerrit.plugins.task.cli.PatchSetArgument;
+import java.io.IOException;
 import java.lang.reflect.Field;
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -26,17 +29,23 @@
 
 /** Use to pre-load a task definition with values from its preload-task definition. */
 public class Preloader {
+  protected final TaskConfigFactory taskConfigFactory;
   protected final Map<TaskExpressionKey, Optional<Task>> optionalTaskByExpression = new HashMap<>();
 
-  public List<Task> getRootTasks(TaskConfig cfg) {
-    return getTasks(cfg, TaskConfig.SECTION_ROOT);
+  @Inject
+  public Preloader(TaskConfigFactory taskConfigFactory) {
+    this.taskConfigFactory = taskConfigFactory;
   }
 
-  public List<Task> getTasks(TaskConfig cfg) {
-    return getTasks(cfg, TaskConfig.SECTION_TASK);
+  public List<Task> getRootTasks() throws IOException, ConfigInvalidException {
+    return getTasks(taskConfigFactory.getRootConfig(), TaskConfig.SECTION_ROOT);
   }
 
-  protected List<Task> getTasks(TaskConfig cfg, String type) {
+  public List<Task> getTasks(FileKey file) throws IOException, ConfigInvalidException {
+    return getTasks(taskConfigFactory.getTaskConfig(file), TaskConfig.SECTION_TASK);
+  }
+
+  protected List<Task> getTasks(TaskConfig cfg, String type) throws IOException {
     List<Task> preloaded = new ArrayList<>();
     for (Task task : cfg.getTasks(type)) {
       try {
@@ -55,27 +64,27 @@
    * @return Optional<Task> which is empty if the expression is optional and no tasks are resolved
    * @throws ConfigInvalidException if the expression requires a task and no tasks are resolved
    */
-  public Optional<Task> getOptionalTask(TaskConfig cfg, TaskExpression expression)
-      throws ConfigInvalidException {
+  public Optional<Task> getOptionalTask(TaskExpression expression)
+      throws ConfigInvalidException, IOException {
     Optional<Task> task = optionalTaskByExpression.get(expression.key);
     if (task == null) {
-      task = preloadOptionalTask(cfg, expression);
+      task = preloadOptionalTask(expression);
       optionalTaskByExpression.put(expression.key, task);
     }
     return task;
   }
 
-  protected Optional<Task> preloadOptionalTask(TaskConfig cfg, TaskExpression expression)
-      throws ConfigInvalidException {
-    Optional<Task> definition = loadOptionalTask(cfg, expression);
+  protected Optional<Task> preloadOptionalTask(TaskExpression expression)
+      throws ConfigInvalidException, IOException {
+    Optional<Task> definition = loadOptionalTask(expression);
     return definition.isPresent() ? Optional.of(preload(definition.get())) : definition;
   }
 
-  public Task preload(Task definition) throws ConfigInvalidException {
+  public Task preload(Task definition) throws ConfigInvalidException, IOException {
     String expression = definition.preloadTask;
     if (expression != null) {
       Optional<Task> preloadFrom =
-          getOptionalTask(definition.config, new TaskExpression(definition.file(), expression));
+          getOptionalTask(new TaskExpression(definition.file(), expression));
       if (preloadFrom.isPresent()) {
         return preloadFrom(definition, preloadFrom.get());
       }
@@ -83,11 +92,11 @@
     return definition;
   }
 
-  protected Optional<Task> loadOptionalTask(TaskConfig cfg, TaskExpression expression)
-      throws ConfigInvalidException {
+  protected Optional<Task> loadOptionalTask(TaskExpression expression)
+      throws ConfigInvalidException, IOException {
     try {
-      for (String name : expression) {
-        Optional<Task> task = cfg.getOptionalTask(name);
+      for (TaskKey key : expression) {
+        Optional<Task> task = getOptionalTask(key);
         if (task.isPresent()) {
           return task;
         }
@@ -117,6 +126,14 @@
     return preloadTo;
   }
 
+  protected Optional<Task> getOptionalTask(TaskKey key) throws IOException, ConfigInvalidException {
+    return taskConfigFactory.getTaskConfig(key.subSection().file()).getOptionalTask(key.task());
+  }
+
+  public void masquerade(PatchSetArgument psa) {
+    taskConfigFactory.masquerade(psa);
+  }
+
   protected static <S, K, V> void preloadField(
       Field field, Task definition, Task preloadFrom, Task preloadTo)
       throws IllegalArgumentException, IllegalAccessException {
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/Properties.java b/src/main/java/com/googlesource/gerrit/plugins/task/Properties.java
index b7284a1..8a13291 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/Properties.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/Properties.java
@@ -14,7 +14,7 @@
 
 package com.googlesource.gerrit.plugins.task;
 
-import com.google.common.collect.Sets;
+import com.google.common.collect.ImmutableSet;
 import com.google.gerrit.entities.Change;
 import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.server.query.change.ChangeData;
@@ -34,15 +34,22 @@
 
 /** Use to expand properties like ${_name} in the text of various definitions. */
 public class Properties {
-  public static final Properties EMPTY_PARENT = new Properties();
+  public static final Properties EMPTY =
+      new Properties() {
+        @Override
+        protected Function<String, String> getParentMapper() {
+          return n -> "";
+        }
+      };
 
-  protected final Properties parentProperties;
+  protected final TaskTree.Node node;
   protected final Task origTask;
   protected final CopyOnWrite<Task> task;
   protected Expander expander;
   protected Loader loader;
   protected boolean init = true;
   protected boolean isTaskRefreshNeeded;
+  protected boolean isApplicableRefreshRequired;
   protected boolean isSubNodeReloadRequired;
 
   public Properties() {
@@ -50,33 +57,27 @@
     expander = new Expander(n -> "");
   }
 
-  public Properties(Task origTask, Properties parentProperties) {
+  public Properties(TaskTree.Node node, Task origTask) {
+    this.node = node;
     this.origTask = origTask;
-    this.parentProperties = parentProperties;
-    task = new CopyOnWrite<>(origTask, t -> origTask.config.new Task(t));
+    task = new CopyOnWrite.CloneOnWrite<>(origTask);
   }
 
   /** Use to expand properties specifically for Tasks. */
   public Task getTask(ChangeData changeData) throws StorageException {
-    if (loader != null && loader.isNonTaskDefinedPropertyLoaded()) {
-      // To detect NamesFactories dependent on non task defined properties, the checking must be
-      // done after subnodes are fully loaded, which unfortunately happens after getTask() is
-      // called. However, these non task property uses from the last change are still detectable
-      // here before we replace the old Loader with a new one.
-      isSubNodeReloadRequired = true;
-    }
-
     loader = new Loader(changeData);
     expander = new Expander(n -> loader.load(n));
-
     if (isTaskRefreshNeeded || init) {
+      expander.expand(task, TaskConfig.KEY_APPLICABLE);
+      isApplicableRefreshRequired = loader.isNonTaskDefinedPropertyLoaded();
+
+      expander.expand(task, ImmutableSet.of(TaskConfig.KEY_APPLICABLE, TaskConfig.KEY_NAME));
+
       Map<String, String> exported = expander.expand(origTask.exported);
       if (exported != origTask.exported) {
         task.getForWrite().exported = exported;
       }
 
-      expander.expand(task, Collections.emptySet());
-
       if (init) {
         init = false;
         isTaskRefreshNeeded = loader.isNonTaskDefinedPropertyLoaded();
@@ -85,31 +86,37 @@
     return task.getForRead();
   }
 
+  // To detect NamesFactories dependent on non task defined properties, the checking must be
+  // done after subnodes are fully loaded, which unfortunately happens after getTask() is
+  // called, therefore this must be called after all subnodes have been loaded.
+  public void expansionComplete() {
+    isSubNodeReloadRequired = loader.isNonTaskDefinedPropertyLoaded();
+  }
+
+  public boolean isApplicableRefreshRequired() {
+    return isApplicableRefreshRequired;
+  }
+
   public boolean isSubNodeReloadRequired() {
     return isSubNodeReloadRequired;
   }
 
   /** Use to expand properties specifically for NamesFactories. */
   public NamesFactory getNamesFactory(NamesFactory namesFactory) {
-    return expander.expand(
-        namesFactory,
-        nf -> namesFactory.config.new NamesFactory(nf),
-        Sets.newHashSet(TaskConfig.KEY_TYPE));
+    return expander.expand(namesFactory, ImmutableSet.of(TaskConfig.KEY_TYPE));
+  }
+
+  protected Function<String, String> getParentMapper() {
+    return n -> node.getParentProperties().expander.getValueForName(n);
   }
 
   protected class Loader {
     protected final ChangeData changeData;
-    protected final Function<String, String> inheritedMapper;
     protected Change change;
     protected boolean isInheritedPropertyLoaded;
 
     public Loader(ChangeData changeData) {
       this.changeData = changeData;
-      if (parentProperties == null || parentProperties.expander == null) {
-        inheritedMapper = n -> "";
-      } else {
-        inheritedMapper = n -> parentProperties.expander.getValueForName(n);
-      }
     }
 
     public boolean isNonTaskDefinedPropertyLoaded() {
@@ -124,7 +131,7 @@
       if (value == null) {
         value = origTask.properties.get(name);
         if (value == null) {
-          value = inheritedMapper.apply(name);
+          value = getParentMapper().apply(name);
           if (!value.isEmpty()) {
             isInheritedPropertyLoaded = true;
           }
@@ -207,7 +214,7 @@
 
     /**
      * Expand all properties (${property_name} -> property_value) in the given text. Returns same
-     * object if no expansions occured.
+     * object if no expansions occurred.
      */
     public Map<String, String> expand(Map<String, String> map) {
       if (map != null) {
@@ -269,7 +276,15 @@
 
     /**
      * Returns expanded object if property found in the Strings in the object's Fields (except the
-     * excluded ones). Returns same object if no expansions occured.
+     * excluded ones). Returns same object if no expansions occurred.
+     */
+    public <C extends Cloneable> C expand(C object, Set<String> excludedFieldNames) {
+      return expand(new CopyOnWrite.CloneOnWrite<>(object), excludedFieldNames);
+    }
+
+    /**
+     * Returns expanded object if property found in the Strings in the object's Fields (except the
+     * excluded ones). Returns same object if no expansions occurred.
      */
     public <T> T expand(T object, Function<T, T> copier, Set<String> excludedFieldNames) {
       return expand(new CopyOnWrite<>(object, copier), excludedFieldNames);
@@ -277,38 +292,59 @@
 
     /**
      * Returns expanded object if property found in the Strings in the object's Fields (except the
-     * excluded ones). Returns same object if no expansions occured.
+     * excluded ones). Returns same object if no expansions occurred.
      */
     public <T> T expand(CopyOnWrite<T> cow, Set<String> excludedFieldNames) {
       for (Field field : cow.getOriginal().getClass().getFields()) {
-        try {
-          if (!excludedFieldNames.contains(field.getName())) {
-            field.setAccessible(true);
-            Object o = field.get(cow.getOriginal());
-            if (o instanceof String) {
-              String expanded = expandText((String) o);
-              if (expanded != o) {
-                field.set(cow.getForWrite(), expanded);
-              }
-            } else if (o instanceof List) {
-              @SuppressWarnings("unchecked")
-              List<String> forceCheck = List.class.cast(o);
-              List<String> expanded = expand(forceCheck);
-              if (expanded != o) {
-                field.set(cow.getForWrite(), expanded);
-              }
-            }
-          }
-        } catch (IllegalAccessException e) {
-          throw new RuntimeException(e);
+        if (!excludedFieldNames.contains(field.getName())) {
+          expand(cow, field);
         }
       }
       return cow.getForRead();
     }
 
     /**
+     * Returns expanded object if property found in the fieldName Field if it is a String, or in the
+     * List's Strings if it is a List. Returns same object if no expansions occurred.
+     */
+    public <T> T expand(CopyOnWrite<T> cow, String fieldName) {
+      try {
+        return expand(cow, cow.getOriginal().getClass().getField(fieldName));
+      } catch (NoSuchFieldException e) {
+        throw new RuntimeException(e);
+      }
+    }
+
+    /**
+     * Returns expanded object if property found in the Field if it is a String, or in the List's
+     * Strings if it is a List. Returns same object if no expansions occurred.
+     */
+    public <T> T expand(CopyOnWrite<T> cow, Field field) {
+      try {
+        field.setAccessible(true);
+        Object o = field.get(cow.getOriginal());
+        if (o instanceof String) {
+          String expanded = expandText((String) o);
+          if (expanded != o) {
+            field.set(cow.getForWrite(), expanded);
+          }
+        } else if (o instanceof List) {
+          @SuppressWarnings("unchecked")
+          List<String> forceCheck = List.class.cast(o);
+          List<String> expanded = expand(forceCheck);
+          if (expanded != o) {
+            field.set(cow.getForWrite(), expanded);
+          }
+        }
+      } catch (IllegalAccessException e) {
+        throw new RuntimeException(e);
+      }
+      return cow.getForRead();
+    }
+
+    /**
      * Returns expanded unmodifiable List if property found. Returns same object if no expansions
-     * occured.
+     * occurred.
      */
     public List<String> expand(List<String> list) {
       if (list != null) {
@@ -325,18 +361,18 @@
     }
 
     /**
-     * Expand all properties (${property_name} -> property_value) in the given text . Returns same
-     * object if no expansions occured.
+     * Expand all properties (${property_name} -> property_value) in the given text. Returns same
+     * object if no expansions occurred.
      */
     public String expandText(String text) {
       if (text == null) {
         return null;
       }
-      StringBuffer out = new StringBuffer();
       Matcher m = PATTERN.matcher(text);
       if (!m.find()) {
         return text;
       }
+      StringBuffer out = new StringBuffer();
       do {
         m.appendReplacement(out, Matcher.quoteReplacement(getValueForName(m.group(1))));
       } while (m.find());
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskAttributeFactory.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskAttributeFactory.java
index ca9f76b..688faa2 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskAttributeFactory.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskAttributeFactory.java
@@ -29,17 +29,21 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 
 public class TaskAttributeFactory implements ChangePluginDefinedInfoFactory {
   private static final FluentLogger log = FluentLogger.forEnclosingClass();
+
   public enum Status {
     INVALID,
     UNKNOWN,
+    DUPLICATE,
     WAITING,
     READY,
     PASS,
@@ -80,7 +84,7 @@
 
   @Override
   public Map<Change.Id, PluginDefinedInfo> createPluginDefinedInfos(
-          Collection<ChangeData> cds, BeanProvider beanProvider, String plugin) {
+      Collection<ChangeData> cds, BeanProvider beanProvider, String plugin) {
     Map<Change.Id, PluginDefinedInfo> pluginInfosByChange = new HashMap<>();
     options = (Modules.MyOptions) beanProvider.getDynamicBean(plugin);
     if (options.all || options.onlyApplicable || options.onlyInvalid) {
@@ -93,13 +97,14 @@
   }
 
   protected PluginDefinedInfo createWithExceptions(ChangeData c) {
+    MatchCache matchCache = new MatchCache(predicateCache, c);
     TaskPluginAttribute a = new TaskPluginAttribute();
     try {
       for (Node node : definitions.getRootNodes(c)) {
-        if (node == null) {
+        if (node instanceof Node.Invalid) {
           a.roots.add(invalid());
         } else {
-          new AttributeFactory(node).create().ifPresent(t -> a.roots.add(t));
+          new AttributeFactory(node, matchCache).create().ifPresent(t -> a.roots.add(t));
         }
       }
     } catch (ConfigInvalidException | IOException | StorageException e) {
@@ -118,10 +123,6 @@
     protected Task task;
     protected TaskAttribute attribute;
 
-    protected AttributeFactory(Node node) {
-      this(node, new MatchCache(predicateCache, node.getChangeData()));
-    }
-
     protected AttributeFactory(Node node, MatchCache matchCache) {
       this.node = node;
       this.matchCache = matchCache;
@@ -137,7 +138,7 @@
 
         boolean applicable = matchCache.match(task.applicable);
         if (!task.isVisible) {
-          if (!task.isTrusted || (!applicable && !options.onlyApplicable)) {
+          if (!node.isTrusted() || (!applicable && !options.onlyApplicable)) {
             return Optional.of(unknown());
           }
         }
@@ -146,8 +147,10 @@
           if (node.isChange()) {
             attribute.change = node.getChangeData().getId().get();
           }
-          attribute.hasPass = task.pass != null || task.fail != null;
-          attribute.subTasks = getSubTasks();
+          attribute.hasPass = !node.isDuplicate && (task.pass != null || task.fail != null);
+          if (!node.isDuplicate) {
+            attribute.subTasks = getSubTasks();
+          }
           attribute.status = getStatus();
           if (options.onlyInvalid && !isValidQueries()) {
             attribute.status = Status.INVALID;
@@ -161,11 +164,13 @@
               if (!options.onlyApplicable) {
                 attribute.applicable = applicable;
               }
-              if (task.inProgress != null) {
-                attribute.inProgress = matchCache.matchOrNull(task.inProgress);
+              if (!node.isDuplicate) {
+                if (task.inProgress != null) {
+                  attribute.inProgress = matchCache.matchOrNull(task.inProgress);
+                }
+                attribute.exported = task.exported.isEmpty() ? null : task.exported;
               }
               attribute.hint = getHint(attribute.status, task);
-              attribute.exported = task.exported.isEmpty() ? null : task.exported;
 
               if (options.evaluationTime) {
                 attribute.evaluationMilliSeconds = millis() - attribute.evaluationMilliSeconds;
@@ -174,16 +179,16 @@
             }
           }
         }
-      } catch (ConfigInvalidException
-          | IOException
-          | QueryParseException
-          | RuntimeException e) {
+      } catch (ConfigInvalidException | IOException | QueryParseException | RuntimeException e) {
         return Optional.of(invalid()); // bad applicability query
       }
       return Optional.empty();
     }
 
     protected Status getStatusWithExceptions() throws StorageException, QueryParseException {
+      if (node.isDuplicate) {
+        return Status.DUPLICATE;
+      }
       if (isAllNull(task.pass, task.fail, attribute.subTasks)) {
         // A leaf def has no defined subdefs.
         boolean hasDefinedSubtasks =
@@ -219,7 +224,8 @@
         }
       }
 
-      if (attribute.subTasks != null && !isAll(attribute.subTasks, Status.PASS)) {
+      if (attribute.subTasks != null
+          && !isAll(attribute.subTasks, EnumSet.of(Status.PASS, Status.DUPLICATE))) {
         // It is possible for a subtask's PASS criteria to change while
         // a parent task is executing, or even after the parent task
         // completes.  This can result in the parent PASS criteria being
@@ -255,8 +261,9 @@
     protected List<TaskAttribute> getSubTasks()
         throws ConfigInvalidException, IOException, StorageException {
       List<TaskAttribute> subTasks = new ArrayList<>();
-      for (Node subNode : node.getSubNodes()) {
-        if (subNode == null) {
+      for (Node subNode :
+          options.onlyApplicable ? node.getSubNodes(matchCache) : node.getSubNodes()) {
+        if (subNode instanceof Node.Invalid) {
           subTasks.add(invalid());
         } else {
           MatchCache subMatchCache = matchCache;
@@ -303,10 +310,16 @@
   }
 
   protected String getHint(Status status, Task def) {
-    if (status == Status.READY) {
-      return def.readyHint;
-    } else if (status == Status.FAIL) {
-      return def.failHint;
+    if (status != null) {
+      switch (status) {
+        case READY:
+          return def.readyHint;
+        case FAIL:
+          return def.failHint;
+        case DUPLICATE:
+          return "Duplicate task is non blocking and empty to break the loop";
+        default:
+      }
     }
     return null;
   }
@@ -320,9 +333,9 @@
     return true;
   }
 
-  protected static boolean isAll(Iterable<TaskAttribute> atts, Status state) {
+  protected static boolean isAll(Iterable<TaskAttribute> atts, Set<Status> states) {
     for (TaskAttribute att : atts) {
-      if (att.status != state) {
+      if (!states.contains(att.status)) {
         return false;
       }
     }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfig.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfig.java
index 81bc735..578ce31 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfig.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfig.java
@@ -14,13 +14,11 @@
 
 package com.googlesource.gerrit.plugins.task;
 
-import com.google.common.collect.Sets;
 import com.google.gerrit.common.Container;
 import com.google.gerrit.entities.BranchNameKey;
 import com.google.gerrit.server.git.meta.AbstractVersionedMetaData;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -55,6 +53,7 @@
 
   public class TaskBase extends SubSection {
     public String applicable;
+    public String duplicateKey;
     public Map<String, String> exported;
     public String fail;
     public String failHint;
@@ -69,13 +68,14 @@
     public List<String> subTasksFiles;
 
     public boolean isVisible;
-    public boolean isTrusted;
+    public boolean isMasqueraded;
 
-    public TaskBase(SubSectionKey s, boolean isVisible, boolean isTrusted) {
+    public TaskBase(SubSectionKey s, boolean isVisible, boolean isMasqueraded) {
       super(s);
       this.isVisible = isVisible;
-      this.isTrusted = isTrusted;
+      this.isMasqueraded = isMasqueraded;
       applicable = getString(s, KEY_APPLICABLE, null);
+      duplicateKey = getString(s, KEY_DUPLICATE_KEY, null);
       exported = getProperties(s, KEY_EXPORT_PREFIX);
       fail = getString(s, KEY_FAIL, null);
       failHint = getString(s, KEY_FAIL_HINT, null);
@@ -92,7 +92,7 @@
 
     protected TaskBase(TaskBase base) {
       this(base.subSection);
-      Copier.deepCopyDeclaredFields(TaskBase.class, base, this, false, copyOnlyReferencesFor());
+      Copier.shallowCopyDeclaredFields(TaskBase.class, base, this, false);
     }
 
     protected TaskBase(SubSectionKey s) {
@@ -100,22 +100,14 @@
     }
   }
 
-  public class Task extends TaskBase {
+  public class Task extends TaskBase implements Cloneable {
     public final TaskKey key;
 
-    public Task(SubSectionKey s, boolean isVisible, boolean isTrusted) {
-      super(s, isVisible, isTrusted);
+    public Task(SubSectionKey s, boolean isVisible, boolean isMasqueraded) {
+      super(s, isVisible, isMasqueraded);
       key = TaskKey.create(s);
     }
 
-    public Task(Task task) {
-      super(task);
-      // Despite being copied in Copier.deepCopyDeclaredFields this
-      // is needed to avoid the final variable initialization warning.
-      this.key = task.key;
-      Copier.deepCopyDeclaredFields(Task.class, task, this, false, copyOnlyReferencesFor());
-    }
-
     public Task(TasksFactory tasks, String name) {
       super(tasks);
       key = TaskKey.create(tasks.subSection, name);
@@ -148,13 +140,13 @@
   public class TasksFactory extends TaskBase {
     public String namesFactory;
 
-    public TasksFactory(SubSectionKey s, boolean isVisible, boolean isTrusted) {
-      super(s, isVisible, isTrusted);
+    public TasksFactory(SubSectionKey s, boolean isVisible, boolean isMasqueraded) {
+      super(s, isVisible, isMasqueraded);
       namesFactory = getString(s, KEY_NAMES_FACTORY, null);
     }
   }
 
-  public class NamesFactory extends SubSection {
+  public class NamesFactory extends SubSection implements Cloneable {
     public String changes;
     public List<String> names;
     public String type;
@@ -165,11 +157,6 @@
       names = getStringList(s, KEY_NAME);
       type = getString(s, KEY_TYPE, null);
     }
-
-    public NamesFactory(NamesFactory n) {
-      super(n.subSection);
-      Copier.deepCopyDeclaredFields(NamesFactory.class, n, this, false, copyOnlyReferencesFor());
-    }
   }
 
   public class External extends SubSection {
@@ -190,10 +177,11 @@
   protected static final String SECTION_EXTERNAL = "external";
   protected static final String SECTION_NAMES_FACTORY = "names-factory";
   protected static final String SECTION_ROOT = "root";
-  protected static final String SECTION_TASK = "task";
+  protected static final String SECTION_TASK = TaskKey.CONFIG_SECTION;
   protected static final String SECTION_TASKS_FACTORY = "tasks-factory";
   protected static final String KEY_APPLICABLE = "applicable";
   protected static final String KEY_CHANGES = "changes";
+  protected static final String KEY_DUPLICATE_KEY = "duplicate-key";
   protected static final String KEY_EXPORT_PREFIX = "export-";
   protected static final String KEY_FAIL = "fail";
   protected static final String KEY_FAIL_HINT = "fail-hint";
@@ -214,25 +202,25 @@
 
   protected final FileKey file;
   public boolean isVisible;
-  public boolean isTrusted;
+  public boolean isMasqueraded;
 
-  public TaskConfig(FileKey file, boolean isVisible, boolean isTrusted) {
-    this(file.branch(), file, isVisible, isTrusted);
+  public TaskConfig(FileKey file, boolean isVisible, boolean isMasqueraded) {
+    this(file.branch(), file, isVisible, isMasqueraded);
   }
 
   public TaskConfig(
-      BranchNameKey masqueraded, FileKey file, boolean isVisible, boolean isTrusted) {
+      BranchNameKey masqueraded, FileKey file, boolean isVisible, boolean isMasqueraded) {
     super(masqueraded, file.file());
     this.file = file;
     this.isVisible = isVisible;
-    this.isTrusted = isTrusted;
+    this.isMasqueraded = isMasqueraded;
   }
 
   protected List<Task> getTasks(String type) {
     List<Task> tasks = new ArrayList<>();
     // No need to get a task with no name (what would we call it?)
     for (String task : cfg.getSubsections(type)) {
-      tasks.add(new Task(subSectionKey(type, task), isVisible, isTrusted));
+      tasks.add(new Task(subSectionKey(type, task), isVisible, isMasqueraded));
     }
     return tasks;
   }
@@ -250,11 +238,11 @@
     SubSectionKey subSection = subSectionKey(SECTION_TASK, name);
     return getNames(subSection).isEmpty()
         ? Optional.empty()
-        : Optional.of(new Task(subSection, isVisible, isTrusted));
+        : Optional.of(new Task(subSection, isVisible, isMasqueraded));
   }
 
   public TasksFactory getTasksFactory(String name) {
-    return new TasksFactory(subSectionKey(SECTION_TASKS_FACTORY, name), isVisible, isTrusted);
+    return new TasksFactory(subSectionKey(SECTION_TASKS_FACTORY, name), isVisible, isMasqueraded);
   }
 
   public NamesFactory getNamesFactory(String name) {
@@ -284,7 +272,7 @@
     for (String name : names) {
       valueByName.put(name, getString(s, name));
     }
-    return valueByName;
+    return Collections.unmodifiableMap(valueByName);
   }
 
   protected Set<String> getMatchingNames(SubSectionKey s, String match) {
@@ -294,7 +282,7 @@
         matched.add(name);
       }
     }
-    return matched;
+    return Collections.unmodifiableSet(matched);
   }
 
   protected Set<String> getNames(SubSectionKey s) {
@@ -318,8 +306,4 @@
   protected SubSectionKey subSectionKey(String section, String subSection) {
     return SubSectionKey.create(file, section, subSection);
   }
-
-  protected Collection<Class<?>> copyOnlyReferencesFor() {
-    return Sets.newHashSet(TaskKey.class, SubSectionKey.class);
-  }
 }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfigFactory.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfigFactory.java
index f8b1dda..908ff0b 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfigFactory.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskConfigFactory.java
@@ -17,9 +17,11 @@
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.entities.BranchNameKey;
 import com.google.gerrit.entities.Project;
+import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.extensions.restapi.AuthException;
 import com.google.gerrit.server.CurrentUser;
 import com.google.gerrit.server.config.AllProjectsName;
+import com.google.gerrit.server.config.AllProjectsNameProvider;
 import com.google.gerrit.server.git.GitRepositoryManager;
 import com.google.gerrit.server.permissions.PermissionBackend;
 import com.google.gerrit.server.permissions.PermissionBackendException;
@@ -45,21 +47,22 @@
   protected final AllProjectsName allProjects;
 
   protected final Map<BranchNameKey, PatchSetArgument> psaMasquerades = new HashMap<>();
+  protected final Map<FileKey, TaskConfig> taskCfgByFile = new HashMap<>();
 
   @Inject
   protected TaskConfigFactory(
-      AllProjectsName allProjects,
+      AllProjectsNameProvider allProjectsNameProvider,
       GitRepositoryManager gitMgr,
       PermissionBackend permissionBackend,
       CurrentUser user) {
-    this.allProjects = allProjects;
+    this.allProjects = allProjectsNameProvider.get();
     this.gitMgr = gitMgr;
     this.permissionBackend = permissionBackend;
     this.user = user;
   }
 
   public TaskConfig getRootConfig() throws ConfigInvalidException, IOException {
-    return getTaskConfig(FileKey.create(getRootBranch(), DEFAULT), true);
+    return getTaskConfig(FileKey.create(getRootBranch(), DEFAULT));
   }
 
   public void masquerade(PatchSetArgument psa) {
@@ -67,26 +70,35 @@
   }
 
   protected BranchNameKey getRootBranch() {
-    return BranchNameKey.create(allProjects, "refs/meta/config");
+    return BranchNameKey.create(allProjects, RefNames.REFS_CONFIG);
   }
 
-  public TaskConfig getTaskConfig(FileKey file, boolean isTrusted)
-      throws ConfigInvalidException, IOException {
+  public TaskConfig getTaskConfig(FileKey key) throws ConfigInvalidException, IOException {
+    TaskConfig cfg = taskCfgByFile.get(key);
+    if (cfg == null) {
+      cfg = loadTaskConfig(key);
+      taskCfgByFile.put(key, cfg);
+    }
+    return cfg;
+  }
+
+  private TaskConfig loadTaskConfig(FileKey file) throws ConfigInvalidException, IOException {
     BranchNameKey branch = file.branch();
     PatchSetArgument psa = psaMasquerades.get(branch);
     boolean visible = true; // invisible psas are filtered out by commandline
+    boolean isMasqueraded = false;
     if (psa == null) {
       visible = canRead(branch);
     } else {
-      isTrusted = false;
+      isMasqueraded = true;
       branch = BranchNameKey.create(psa.change.getProject(), psa.patchSet.refName());
     }
 
     Project.NameKey project = file.branch().project();
     TaskConfig cfg =
-        psa == null
-            ? new TaskConfig(file, visible, isTrusted)
-            : new TaskConfig(branch, file, visible, isTrusted);
+        isMasqueraded
+            ? new TaskConfig(branch, file, visible, isMasqueraded)
+            : new TaskConfig(file, visible, isMasqueraded);
     try (Repository git = gitMgr.openRepository(project)) {
       cfg.load(project, git);
     } catch (IOException e) {
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpression.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpression.java
index 90dffff..5a61d29 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpression.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskExpression.java
@@ -35,7 +35,7 @@
  *   <li><code> "foo | bar |"   -> ("foo", "bar")     optional</code>
  * </ul>
  */
-public class TaskExpression implements Iterable<String> {
+public class TaskExpression implements Iterable<TaskKey> {
   protected static final Pattern EXPRESSION_PATTERN = Pattern.compile("([^ |]+[^|]*)(\\|)?");
   protected final TaskExpressionKey key;
 
@@ -44,8 +44,8 @@
   }
 
   @Override
-  public Iterator<String> iterator() {
-    return new Iterator<String>() {
+  public Iterator<TaskKey> iterator() {
+    return new Iterator<TaskKey>() {
       Matcher m = EXPRESSION_PATTERN.matcher(key.expression());
       Boolean hasNext;
       boolean optional;
@@ -65,13 +65,14 @@
       }
 
       @Override
-      public String next() {
-        hasNext(); // in case next() was (re)called w/o calling hasNext()
+      public TaskKey next() {
+        // Can't use @SuppressWarnings("ReturnValueIgnored") on method call
+        boolean ignored = hasNext(); // in case next() was (re)called w/o calling hasNext()
         if (!hasNext) {
           throw new NoSuchElementException("No more names, yet expression was not optional");
         }
         hasNext = null;
-        return m.group(1).trim();
+        return TaskKey.create(key.file(), m.group(1).trim());
       }
     };
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskKey.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskKey.java
index 7f1426a..c56202d 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskKey.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskKey.java
@@ -20,11 +20,18 @@
 /** An immutable reference to a task in task config file. */
 @AutoValue
 public abstract class TaskKey {
+  protected static final String CONFIG_SECTION = "task";
+
   /** Creates a TaskKey with task name as the name of sub section. */
   public static TaskKey create(SubSectionKey section) {
     return create(section, section.subSection());
   }
 
+  /** Creates a TaskKey with given FileKey and task name and sub section's name as 'task'. */
+  public static TaskKey create(FileKey file, String task) {
+    return create(SubSectionKey.create(file, CONFIG_SECTION, task));
+  }
+
   /** Creates a TaskKey from a sub section and task name, generally used by TasksFactory. */
   public static TaskKey create(SubSectionKey section, String task) {
     return new AutoValue_TaskKey(section, task);
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskStatus.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskStatus.java
new file mode 100644
index 0000000..5dc7afd
--- /dev/null
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskStatus.java
@@ -0,0 +1,27 @@
+// Copyright (C) 2022 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.googlesource.gerrit.plugins.task;
+
+public class TaskStatus {
+  public enum Status {
+    INVALID,
+    UNKNOWN,
+    DUPLICATE,
+    WAITING,
+    READY,
+    PASS,
+    FAIL;
+  }
+}
diff --git a/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java b/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java
index 8e4fd37..47b9e75 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/task/TaskTree.java
@@ -14,6 +14,8 @@
 
 package com.googlesource.gerrit.plugins.task;
 
+import static java.util.stream.Collectors.toList;
+
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.entities.Account;
 import com.google.gerrit.entities.BranchNameKey;
@@ -70,11 +72,11 @@
   protected final AccountResolver accountResolver;
   protected final AllUsersNameProvider allUsers;
   protected final CurrentUser user;
-  protected final TaskConfigFactory taskFactory;
   protected final Preloader preloader;
   protected final NodeList root = new NodeList();
   protected final Provider<ChangeQueryBuilder> changeQueryBuilderProvider;
   protected final Provider<ChangeQueryProcessor> changeQueryProcessorProvider;
+  protected final Map<SubSectionKey, List<Task>> definitionsBySubSection = new HashMap<>();
 
   protected ChangeData changeData;
 
@@ -84,119 +86,148 @@
       AllUsersNameProvider allUsers,
       AnonymousUser anonymousUser,
       CurrentUser user,
-      TaskConfigFactory taskFactory,
       Provider<ChangeQueryBuilder> changeQueryBuilderProvider,
       Provider<ChangeQueryProcessor> changeQueryProcessorProvider,
       Preloader preloader) {
     this.accountResolver = accountResolver;
     this.allUsers = allUsers;
     this.user = user != null ? user : anonymousUser;
-    this.taskFactory = taskFactory;
     this.changeQueryProcessorProvider = changeQueryProcessorProvider;
     this.changeQueryBuilderProvider = changeQueryBuilderProvider;
     this.preloader = preloader;
   }
 
   public void masquerade(PatchSetArgument psa) {
-    taskFactory.masquerade(psa);
+    preloader.masquerade(psa);
   }
 
   public List<Node> getRootNodes(ChangeData changeData)
       throws ConfigInvalidException, IOException, StorageException {
     this.changeData = changeData;
     root.path = Collections.emptyList();
+    root.duplicateKeys = Collections.emptyList();
     return root.getSubNodes();
   }
 
   protected class NodeList {
     protected NodeList parent = null;
     protected Collection<String> path;
+    protected Collection<String> duplicateKeys;
     protected Map<TaskKey, Node> cachedNodeByTask = new HashMap<>();
-    protected List<Node> nodes;
-    protected Set<String> names = new HashSet<>();
+    protected List<Node> cachedNodes;
 
-    protected void addSubNodes() throws ConfigInvalidException, IOException, StorageException {
-      addPreloaded(preloader.getRootTasks(taskFactory.getRootConfig()));
-    }
-
-    protected void addPreloaded(List<Task> defs) throws ConfigInvalidException, StorageException {
-      for (Task def : defs) {
-        addPreloaded(def);
+    protected List<Node> getSubNodes()
+        throws ConfigInvalidException, IOException, StorageException {
+      if (cachedNodes != null) {
+        return refresh(cachedNodes);
       }
+      return cachedNodes = loadSubNodes();
     }
 
-    protected void addPreloaded(Task def) throws ConfigInvalidException, StorageException {
-      addPreloaded(def, (parent, definition) -> new Node(parent, definition));
-    }
-
-    protected void addPreloaded(Task def, NodeFactory nodeFactory)
-        throws ConfigInvalidException, StorageException {
-      if (def != null) {
-        try {
-          Node node = cachedNodeByTask.get(def.key());
-          boolean isRefreshNeeded = node != null;
-          if (node == null) {
-            node = nodeFactory.create(this, def);
-          }
-
-          if (!path.contains(node.key()) && names.add(def.name())) {
-            // path check above detects looping definitions
-            // names check above detects duplicate subtasks
-            if (isRefreshNeeded) {
-              node.refreshTask();
-            }
-            nodes.add(node);
-            return;
-          }
-        } catch (Exception e) {
-        }
-      }
-      addInvalidNode();
-    }
-
-    protected void addInvalidNode() {
-      nodes.add(null); // null node indicates invalid
-    }
-
-    protected List<Node> getSubNodes() throws ConfigInvalidException, IOException, StorageException {
-      if (nodes == null) {
-        nodes = new ArrayList<>();
-        addSubNodes();
-      } else {
-        refreshSubNodes();
-      }
-      return nodes;
-    }
-
-    public void refreshSubNodes() throws ConfigInvalidException, StorageException {
-      if (nodes != null) {
-        for (Node node : nodes) {
-          if (node != null) {
-            node.refreshTask();
-          }
-        }
-      }
+    protected List<Node> loadSubNodes()
+        throws ConfigInvalidException, IOException, StorageException {
+      return new SubNodeFactory().createFromPreloaded(preloader.getRootTasks());
     }
 
     public ChangeData getChangeData() {
-      return parent == null ? TaskTree.this.changeData : parent.getChangeData();
+      return TaskTree.this.changeData;
     }
 
-    protected Properties getProperties() {
-      return Properties.EMPTY_PARENT;
+    protected boolean isTrusted() {
+      return true;
+    }
+
+    protected class SubNodeFactory {
+      protected Set<String> names = new HashSet<>();
+
+      public List<Node> createFromPreloaded(List<Task> defs)
+          throws ConfigInvalidException, StorageException {
+        List<Node> nodes = new ArrayList<>();
+        for (Task def : defs) {
+          nodes.add(createFromPreloaded(def));
+        }
+        return nodes;
+      }
+
+      public Node createFromPreloaded(Task def) throws ConfigInvalidException, StorageException {
+        return createFromPreloaded(def, (parent, definition) -> new Node(parent, definition));
+      }
+
+      public Node createFromPreloaded(Task def, ChangeData changeData)
+          throws ConfigInvalidException, StorageException {
+        return createFromPreloaded(
+            def,
+            (parent, definition) ->
+                new Node(parent, definition) {
+                  @Override
+                  public ChangeData getChangeData() {
+                    return changeData;
+                  }
+
+                  @Override
+                  public boolean isChange() {
+                    return true;
+                  }
+                });
+      }
+
+      protected Node createFromPreloaded(Task def, NodeFactory nodeFactory)
+          throws ConfigInvalidException, StorageException {
+        if (def != null) {
+          try {
+            Node node = cachedNodeByTask.get(def.key());
+            boolean isRefreshNeeded = node != null;
+            if (node == null) {
+              node = nodeFactory.create(NodeList.this, def);
+            }
+
+            if (names.add(def.name())) {
+              // names check above detects duplicate subtasks
+              if (isRefreshNeeded) {
+                node.refreshTask();
+              }
+              return node;
+            }
+          } catch (Exception e) {
+          }
+        }
+        return createInvalid();
+      }
+
+      protected Node createInvalid() {
+        return new Node().new Invalid();
+      }
     }
   }
 
   public class Node extends NodeList {
+    public class Invalid extends Node {
+      @Override
+      public void refreshTask() throws ConfigInvalidException, StorageException {}
+
+      @Override
+      public Task getDefinition() {
+        return null;
+      }
+    }
+
     public Task task;
+    public boolean isDuplicate;
 
     protected final Properties properties;
     protected final TaskKey taskKey;
+    protected Map<BranchNameKey, List<Node>> nodesByBranch;
+    protected boolean hasUnfilterableSubNodes = false;
+
+    protected Node() { // Only for Invalid
+      taskKey = null;
+      properties = null;
+    }
 
     public Node(NodeList parent, Task task) throws ConfigInvalidException, StorageException {
       this.parent = parent;
       taskKey = task.key();
-      properties = new Properties(task, parent.getProperties());
+      properties = new Properties(this, task);
       refreshTask();
     }
 
@@ -204,153 +235,291 @@
       return String.valueOf(getChangeData().getId().get()) + TaskConfig.SEP + taskKey;
     }
 
+    public List<Node> getSubNodes() throws ConfigInvalidException, IOException, StorageException {
+      if (cachedNodes != null) {
+        return refresh(cachedNodes);
+      }
+      List<Node> nodes = loadSubNodes();
+      if (!properties.isSubNodeReloadRequired()) {
+        if (!isChange()) {
+          return cachedNodes = nodes;
+        }
+        definitionsBySubSection.computeIfAbsent(
+            task.key().subSection(),
+            k -> nodes.stream().map(n -> n.getDefinition()).collect(toList()));
+      } else {
+        hasUnfilterableSubNodes = true;
+        cachedNodeByTask.clear();
+        nodes.stream()
+            .filter(n -> !(n instanceof Invalid) && !n.isChange())
+            .forEach(n -> cachedNodeByTask.put(n.task.key(), n));
+      }
+      return nodes;
+    }
+
+    public List<Node> getSubNodes(MatchCache matchCache)
+        throws ConfigInvalidException, IOException, StorageException {
+      if (hasUnfilterableSubNodes) {
+        return getSubNodes();
+      }
+      return new ApplicableNodeFilter(matchCache).getSubNodes();
+    }
+
+    @Override
+    protected List<Node> loadSubNodes()
+        throws ConfigInvalidException, IOException, StorageException {
+      List<Task> cachedDefinitions = definitionsBySubSection.get(task.key().subSection());
+      if (cachedDefinitions != null) {
+        return new SubNodeFactory().createFromPreloaded(cachedDefinitions);
+      }
+      List<Node> nodes = new SubNodeAdder().getSubNodes();
+      properties.expansionComplete();
+      return nodes;
+    }
+
     /* The task needs to be refreshed before a node is used, however
     subNode refreshing can wait until they are fetched since they may
     not be needed. */
     public void refreshTask() throws ConfigInvalidException, StorageException {
       this.path = new LinkedList<>(parent.path);
-      this.path.add(key());
+      String key = key();
+      isDuplicate = path.contains(key);
+      path.add(key);
 
       this.task = properties.getTask(getChangeData());
 
-      if (nodes != null && properties.isSubNodeReloadRequired()) {
-        cachedNodeByTask.clear();
-        nodes.stream().filter(n -> n != null).forEach(n -> cachedNodeByTask.put(n.task.key(), n));
-        names.clear();
-        nodes = null;
+      this.duplicateKeys = new LinkedList<>(parent.duplicateKeys);
+      if (task.duplicateKey != null) {
+        isDuplicate |= duplicateKeys.contains(task.duplicateKey);
+        duplicateKeys.add(task.duplicateKey);
       }
     }
 
+    protected Properties getParentProperties() {
+      return (parent instanceof Node) ? ((Node) parent).properties : Properties.EMPTY;
+    }
+
     @Override
-    protected void addSubNodes() throws ConfigInvalidException, StorageException {
-      addSubTasks();
-      addSubTasksFactoryTasks();
-      addSubTasksFiles();
-      addSubTasksExternals();
-    }
-
-    protected void addSubTasks() throws ConfigInvalidException, StorageException {
-      for (String expression : task.subTasks) {
-        try {
-          Optional<Task> def =
-              preloader.getOptionalTask(task.config, new TaskExpression(task.file(), expression));
-          if (def.isPresent()) {
-            addPreloaded(def.get());
-          }
-        } catch (ConfigInvalidException e) {
-          addInvalidNode();
-        }
-      }
-    }
-
-    protected void addSubTasksFiles() throws ConfigInvalidException, StorageException {
-      for (String file : task.subTasksFiles) {
-        try {
-          addPreloaded(
-              getPreloadedTasks(FileKey.create(task.key().branch(), resolveTaskFileName(file))));
-        } catch (ConfigInvalidException | IOException e) {
-          addInvalidNode();
-        }
-      }
-    }
-
-    protected void addSubTasksExternals() throws ConfigInvalidException, StorageException {
-      for (String external : task.subTasksExternals) {
-        try {
-          External ext = task.config.getExternal(external);
-          if (ext == null) {
-            addInvalidNode();
-          } else {
-            addPreloaded(getPreloadedTasks(ext));
-          }
-        } catch (ConfigInvalidException | IOException e) {
-          addInvalidNode();
-        }
-      }
-    }
-
-    protected void addSubTasksFactoryTasks() throws ConfigInvalidException,     StorageException {
-      for (String tasksFactoryName : task.subTasksFactories) {
-        TasksFactory tasksFactory = task.config.getTasksFactory(tasksFactoryName);
-        if (tasksFactory != null) {
-          NamesFactory namesFactory = task.config.getNamesFactory(tasksFactory.namesFactory);
-          if (namesFactory != null && namesFactory.type != null) {
-            namesFactory = getProperties().getNamesFactory(namesFactory);
-            switch (NamesFactoryType.getNamesFactoryType(namesFactory.type)) {
-              case STATIC:
-                addStaticTypeTasks(tasksFactory, namesFactory);
-                continue;
-              case CHANGE:
-                addChangeTypeTasks(tasksFactory, namesFactory);
-                continue;
-            }
-          }
-        }
-        addInvalidNode();
-      }
-    }
-
-    protected void addStaticTypeTasks(TasksFactory tasksFactory, NamesFactory namesFactory)
-        throws ConfigInvalidException, StorageException {
-      for (String name : namesFactory.names) {
-        addPreloaded(preloader.preload(task.config.new Task(tasksFactory, name)));
-      }
-    }
-
-    protected void addChangeTypeTasks(TasksFactory tasksFactory, NamesFactory namesFactory)
-        throws ConfigInvalidException, StorageException {
-      try {
-        if (namesFactory.changes != null) {
-          List<ChangeData> changeDataList =
-              changeQueryProcessorProvider
-                  .get()
-                  .query(changeQueryBuilderProvider.get().parse(namesFactory.changes))
-                  .entities();
-          for (ChangeData changeData : changeDataList) {
-            addPreloaded(
-                preloader.preload(
-                    task.config.new Task(tasksFactory, changeData.getId().toString())),
-                (parent, definition) ->
-                    new Node(parent, definition) {
-                      @Override
-                      public ChangeData getChangeData() {
-                        return changeData;
-                      }
-
-                      @Override
-                      public boolean isChange() {
-                        return true;
-                      }
-                    });
-          }
-          return;
-        }
-      } catch (StorageException e) {
-        log.atSevere().withCause(e).log("ERROR: running changes query: " + namesFactory.changes);
-      } catch (QueryParseException e) {
-      }
-      addInvalidNode();
-    }
-
-    protected List<Task> getPreloadedTasks(External external)
-        throws ConfigInvalidException, IOException, StorageException {
-      return getPreloadedTasks(
-          FileKey.create(resolveUserBranch(external.user), resolveTaskFileName(external.file)));
-    }
-
-    protected List<Task> getPreloadedTasks(FileKey file)
-        throws ConfigInvalidException, IOException {
-      return preloader.getTasks(taskFactory.getTaskConfig(file, task.isTrusted));
+    protected boolean isTrusted() {
+      return parent.isTrusted() && !task.isMasqueraded;
     }
 
     @Override
-    protected Properties getProperties() {
-      return properties;
+    public ChangeData getChangeData() {
+      return parent.getChangeData();
+    }
+
+    public Task getDefinition() {
+      return properties.origTask;
     }
 
     public boolean isChange() {
       return false;
     }
+
+    protected class SubNodeAdder {
+      protected List<Node> nodes = new ArrayList<>();
+      protected SubNodeFactory factory = new SubNodeFactory();
+
+      public List<Node> getSubNodes() throws ConfigInvalidException, IOException, StorageException {
+        addSubTasks();
+        addSubTasksFactoryTasks();
+        addSubTasksFiles();
+        addSubTasksExternals();
+        return nodes;
+      }
+
+      protected void addSubTasks() throws ConfigInvalidException, IOException, StorageException {
+        for (String expression : task.subTasks) {
+          try {
+            Optional<Task> def =
+                preloader.getOptionalTask(new TaskExpression(task.file(), expression));
+            if (def.isPresent()) {
+              addPreloaded(def.get());
+            }
+          } catch (ConfigInvalidException e) {
+            addInvalidNode();
+          }
+        }
+      }
+
+      protected void addSubTasksFiles() throws ConfigInvalidException, StorageException {
+        for (String file : task.subTasksFiles) {
+          try {
+            addPreloaded(
+                preloader.getTasks(FileKey.create(task.key().branch(), resolveTaskFileName(file))));
+          } catch (ConfigInvalidException | IOException e) {
+            addInvalidNode();
+          }
+        }
+      }
+
+      protected void addSubTasksExternals() throws ConfigInvalidException, StorageException {
+        for (String external : task.subTasksExternals) {
+          try {
+            External ext = task.config.getExternal(external);
+            if (ext == null) {
+              addInvalidNode();
+            } else {
+              addPreloaded(getPreloadedTasks(ext));
+            }
+          } catch (ConfigInvalidException | IOException e) {
+            addInvalidNode();
+          }
+        }
+      }
+
+      protected void addSubTasksFactoryTasks()
+          throws ConfigInvalidException, IOException, StorageException {
+        for (String tasksFactoryName : task.subTasksFactories) {
+          TasksFactory tasksFactory = task.config.getTasksFactory(tasksFactoryName);
+          if (tasksFactory != null) {
+            NamesFactory namesFactory = task.config.getNamesFactory(tasksFactory.namesFactory);
+            if (namesFactory != null && namesFactory.type != null) {
+              namesFactory = properties.getNamesFactory(namesFactory);
+              switch (NamesFactoryType.getNamesFactoryType(namesFactory.type)) {
+                case STATIC:
+                  addStaticTypeTasks(tasksFactory, namesFactory);
+                  continue;
+                case CHANGE:
+                  addChangeTypeTasks(tasksFactory, namesFactory);
+                  continue;
+              }
+            }
+          }
+          addInvalidNode();
+        }
+      }
+
+      protected void addStaticTypeTasks(TasksFactory tasksFactory, NamesFactory namesFactory)
+          throws ConfigInvalidException, IOException, StorageException {
+        for (String name : namesFactory.names) {
+          addPreloaded(preloader.preload(task.config.new Task(tasksFactory, name)));
+        }
+      }
+
+      protected void addChangeTypeTasks(TasksFactory tasksFactory, NamesFactory namesFactory)
+          throws ConfigInvalidException, IOException, StorageException {
+        try {
+          if (namesFactory.changes != null) {
+            List<ChangeData> changeDataList =
+                changeQueryProcessorProvider
+                    .get()
+                    .query(changeQueryBuilderProvider.get().parse(namesFactory.changes))
+                    .entities();
+            for (ChangeData changeData : changeDataList) {
+              addPreloaded(
+                  preloader.preload(
+                      task.config.new Task(tasksFactory, changeData.getId().toString())),
+                  changeData);
+            }
+            return;
+          }
+        } catch (StorageException e) {
+          log.atSevere().withCause(e).log("ERROR: running changes query: " + namesFactory.changes);
+        } catch (QueryParseException e) {
+        }
+        addInvalidNode();
+      }
+
+      public void addPreloaded(List<Task> defs) throws ConfigInvalidException, StorageException {
+        nodes.addAll(factory.createFromPreloaded(defs));
+      }
+
+      public void addPreloaded(Task def, ChangeData changeData)
+          throws ConfigInvalidException, StorageException {
+        nodes.add(factory.createFromPreloaded(def, changeData));
+      }
+
+      public void addPreloaded(Task def) throws ConfigInvalidException, StorageException {
+        nodes.add(factory.createFromPreloaded(def));
+      }
+
+      public void addInvalidNode() {
+        nodes.add(factory.createInvalid());
+      }
+
+      protected List<Task> getPreloadedTasks(External external)
+          throws ConfigInvalidException, IOException, StorageException {
+        return preloader.getTasks(
+            FileKey.create(resolveUserBranch(external.user), resolveTaskFileName(external.file)));
+      }
+    }
+
+    public class ApplicableNodeFilter {
+      protected MatchCache matchCache;
+      protected PredicateCache pcache;
+      protected BranchNameKey branch = getChangeData().change().getDest();
+
+      public ApplicableNodeFilter(MatchCache matchCache)
+          throws ConfigInvalidException, IOException, StorageException {
+        this.matchCache = matchCache;
+        this.pcache = matchCache.predicateCache;
+      }
+
+      public List<Node> getSubNodes() throws ConfigInvalidException, IOException, StorageException {
+        if (nodesByBranch != null) {
+          List<Node> nodes = nodesByBranch.get(branch);
+          if (nodes != null) {
+            return refresh(nodes);
+          }
+        }
+
+        List<Node> nodes = Node.this.getSubNodes();
+        if (!hasUnfilterableSubNodes && !nodes.isEmpty()) {
+          Optional<List<Node>> filterable = getOptionalApplicableForBranch(nodes);
+          if (filterable.isPresent()) {
+            if (nodesByBranch == null) {
+              nodesByBranch = new HashMap<>();
+            }
+            nodesByBranch.put(branch, filterable.get());
+            return filterable.get();
+          }
+          hasUnfilterableSubNodes = true;
+        }
+        return nodes;
+      }
+
+      protected Optional<List<Node>> getOptionalApplicableForBranch(List<Node> nodes)
+          throws ConfigInvalidException, IOException, StorageException {
+        int filterable = 0;
+        List<Node> applicableNodes = new ArrayList<>();
+        for (Node node : nodes) {
+          if (node instanceof Invalid) {
+            filterable++;
+          } else if (isApplicableCacheableByBranch(node)) {
+            filterable++;
+            try {
+              if (!matchCache.match(node.task.applicable)) {
+                // Correctness will not be affected if more nodes are added than necessary
+                // (i.e. if isApplicableCacheableByBranch() does not realize a Node is cacheable
+                // based on its Branch), but it is incorrect to filter out a Node now that could
+                // later be applicable when a property, other than its Change's destination, is
+                // altered.
+                continue;
+              }
+            } catch (QueryParseException e) {
+            }
+          }
+          applicableNodes.add(node);
+        }
+        // Simple heuristic to determine whether storing the filtered nodes is worth it. There
+        // is minor evidence to suggest that storing a large list actually hurts performance.
+        return (filterable > nodes.size() / 2) ? Optional.of(applicableNodes) : Optional.empty();
+      }
+
+      protected boolean isApplicableCacheableByBranch(Node node) {
+        String applicable = node.task.applicable;
+        if (node.properties.isApplicableRefreshRequired()) {
+          return false;
+        }
+        try {
+          return pcache.isCacheableByBranch(applicable);
+        } catch (QueryParseException e) {
+          return false;
+        }
+      }
+    }
   }
 
   protected String resolveTaskFileName(String file) throws ConfigInvalidException {
@@ -377,4 +546,12 @@
     }
     return BranchNameKey.create(allUsers.get(), RefNames.refsUsers(acct));
   }
+
+  protected static List<Node> refresh(List<Node> nodes)
+      throws ConfigInvalidException, StorageException {
+    for (Node node : nodes) {
+      node.refreshTask();
+    }
+    return nodes;
+  }
 }
diff --git a/src/main/resources/Documentation/config-gerrit.md b/src/main/resources/Documentation/config-gerrit.md
new file mode 100644
index 0000000..6f0b0a5
--- /dev/null
+++ b/src/main/resources/Documentation/config-gerrit.md
@@ -0,0 +1,25 @@
+# Admin User Guide - Configuration
+
+## File `etc/gerrit.config`
+
+The file `'$site_path'/etc/gerrit.config` is a Git-style config file
+that controls many host specific settings for Gerrit.
+
+### Section @PLUGIN@ "cacheable-predicates"
+
+The @PLUGIN@.cacheable-predicates section configures Change Predicate
+optimizations which the @PLUGIN@ plugin may use when evaluating tasks.
+
+#### @PLUGIN@.cacheable-predicates.byBranch-className
+
+The value set with this key specifies a fully qualified class name
+of a Predicate which can be assumed to always return the same match
+result to all Changes destined for the same project/branch
+combinations. This key may be specified more than once.
+
+Example:
+
+```
+[@PLUGIN@ "cacheable-predicates"]
+        byBranch-className = com.google.gerrit.server.query.change.BranchSetPredicate
+```
\ No newline at end of file
diff --git a/src/main/resources/Documentation/task.md b/src/main/resources/Documentation/task.md
index fa5e834..ce2dd40 100644
--- a/src/main/resources/Documentation/task.md
+++ b/src/main/resources/Documentation/task.md
@@ -51,11 +51,17 @@
 completes.
 
 A task with a `WAITING` status is not yet ready to execute. A task in this
-state is blocked by its subtasks which are not yet in the `PASS` state.
+state is blocked by its subtasks which are not yet in the `PASS` or `DUPLICATE`
+state.
 
 A task with a `READY` status is ready to be executed. All of its subtasks are
 in the `PASS` state.
 
+A task with a `DUPLICATE` status has the same task key as one of its ancestors.
+Task keys are generally made up of the canonical task name and the change to
+which it applies. To avoid infinite loops, subtasks are ignored on duplicate
+tasks.
+
 A task with a `PASS` status meets all the criteria for `READY`, and has
 executed and was successful.
 
@@ -231,6 +237,48 @@
     subtasks-file = common.config  # references the file named task/common.config
 ```
 
+`duplicate-key`
+
+: This key defines an identifier to help identify tasks which should be
+considered duplicates even if they are not exact duplicates. When the task
+plugin encounters a task with the same duplicate-key as one of its
+ancestors, it will be considered a duplicate of that ancestor. Tasks such as
+a starting task and a looping tasks-factory that preload the same base task
+are not exact duplicates, yet they may logically represent duplicates. In
+this case, defining a `duplicate-key` on the base task which is preloaded
+from two different places (usually a root and a change tasks-factory), will
+ensure that any loops are halted once the original change is reached. Without
+a duplicate-key, the walking would generally walk one task further than
+desired.
+
+Outlined below is a simple way to walk a change's git dependencies in the
+task plugin. While Git does not allow loops in commit histories, sometimes
+in Gerrit when changes get rebased, it can cause loops (because Gerrit
+sometimes tracks outdated dependencies). The use of the duplicate-key
+below results in the loop being detected when you would expect it to be.
+
+Example:
+
+```
+[root "git dependencies"]
+    applicable = status:new
+    preload-task = git dependencies
+
+[task "git dependencies"]
+    fail = -status:new
+    fail-hint = [${_change_status}] dependency needs to be OPEN
+    subtasks-factory = git dependencies
+    duplicate-key = git dependencies ${_change_number}
+
+[tasks-factory "git dependencies"]
+    names-factory = git dependencies
+    preload-task = git dependencies
+
+[names-factory "git dependencies"]
+    type = change
+    changes = -status:merged parentof:${_change_number} project:${_change_project} branch:${_change_branch}
+```
+
 Root Tasks
 ----------
 Root tasks typically define the "final verification" tasks for changes. Each
diff --git a/src/main/resources/Documentation/test/preview.md b/src/main/resources/Documentation/test/preview.md
index 1aeb649..6aff577 100644
--- a/src/main/resources/Documentation/test/preview.md
+++ b/src/main/resources/Documentation/test/preview.md
@@ -122,18 +122,6 @@
          "status" : "INVALID"   # Only Test Suite: invalid
       },
       {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "Looping",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "name" : "UNKNOWN",
-               "status" : "INVALID"
-            }
-         ]
-      },
-      {
          "name" : "UNKNOWN",
          "status" : "INVALID"
       },
@@ -226,106 +214,6 @@
                "status" : "INVALID"
             }
          ]
-      },
-      {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "task (tasks-factory changes loop)",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "applicable" : true,
-               "change" : _change1_number,
-               "hasPass" : true,
-               "name" : "_change1_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        },
-                        {
-                           "applicable" : true,
-                           "change" : _change2_number,
-                           "hasPass" : true,
-                           "name" : "_change2_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        }
-                     ]
-                  }
-               ]
-            },
-            {
-               "applicable" : true,
-               "change" : _change2_number,
-               "hasPass" : true,
-               "name" : "_change2_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "applicable" : true,
-                           "change" : _change1_number,
-                           "hasPass" : true,
-                           "name" : "_change1_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        },
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        }
-                     ]
-                  }
-               ]
-            }
-         ]
       }
    ]
 }
@@ -536,18 +424,6 @@
          "status" : "INVALID"   # Only Test Suite: invalid
       },
       {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "Looping",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "name" : "UNKNOWN",
-               "status" : "INVALID"
-            }
-         ]
-      },
-      {
          "name" : "UNKNOWN",
          "status" : "INVALID"
       },
@@ -640,106 +516,6 @@
                "status" : "INVALID"
             }
          ]
-      },
-      {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "task (tasks-factory changes loop)",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "applicable" : true,
-               "change" : _change1_number,
-               "hasPass" : true,
-               "name" : "_change1_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        },
-                        {
-                           "applicable" : true,
-                           "change" : _change2_number,
-                           "hasPass" : true,
-                           "name" : "_change2_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        }
-                     ]
-                  }
-               ]
-            },
-            {
-               "applicable" : true,
-               "change" : _change2_number,
-               "hasPass" : true,
-               "name" : "_change2_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "applicable" : true,
-                           "change" : _change1_number,
-                           "hasPass" : true,
-                           "name" : "_change1_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        },
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        }
-                     ]
-                  }
-               ]
-            }
-         ]
       }
    ]
 }
diff --git a/src/main/resources/Documentation/test/task_states.md b/src/main/resources/Documentation/test/task_states.md
index e9cc8b6..f48f528 100644
--- a/src/main/resources/Documentation/test/task_states.md
+++ b/src/main/resources/Documentation/test/task_states.md
@@ -1183,6 +1183,99 @@
    ]
 }
 
+[root "Root applicable Property"]
+  subtask = Subtask applicable Property
+  subtasks-factory = tasks-factory branch NOT applicable Property
+
+[tasks-factory "tasks-factory branch NOT applicable Property"]
+  names-factory = names-factory branch NOT applicable Property
+  applicable = branch:dev
+  fail = True
+
+[names-factory "names-factory branch NOT applicable Property"]
+  type = static
+  name = NOT Applicable 1
+  name = NOT Applicable 2
+  name = NOT Applicable 3
+
+[task "Subtask applicable Property"]
+  applicable = change:${_change_number}
+  fail = True
+
+{
+   "applicable" : true,
+   "hasPass" : false,
+   "name" : "Root applicable Property",
+   "status" : "WAITING",
+   "subTasks" : [
+      {
+         "applicable" : true,
+         "hasPass" : true,
+         "name" : "Subtask applicable Property",
+         "status" : "FAIL"
+      },                              # Only Test Suite: all
+      {                               # Only Test Suite: all
+         "applicable" : false,        # Only Test Suite: all
+         "hasPass" : true,            # Only Test Suite: all
+         "name" : "NOT Applicable 1", # Only Test Suite: all
+         "status" : "FAIL"            # Only Test Suite: all
+      },                              # Only Test Suite: all
+      {                               # Only Test Suite: all
+         "applicable" : false,        # Only Test Suite: all
+         "hasPass" : true,            # Only Test Suite: all
+         "name" : "NOT Applicable 2", # Only Test Suite: all
+         "status" : "FAIL"            # Only Test Suite: all
+      },                              # Only Test Suite: all
+      {                               # Only Test Suite: all
+         "applicable" : false,        # Only Test Suite: all
+         "hasPass" : true,            # Only Test Suite: all
+         "name" : "NOT Applicable 3", # Only Test Suite: all
+         "status" : "FAIL"            # Only Test Suite: all
+      }
+   ]
+}
+
+[root "Root branch applicable Property"]
+  subtasks-factory = tasks-factory branch applicable Property
+
+[tasks-factory "tasks-factory branch applicable Property"]
+  names-factory = names-factory branch applicable Property
+  applicable = branch:master
+  fail = True
+
+[names-factory "names-factory branch applicable Property"]
+  type = static
+  name = Applicable 1
+  name = Applicable 2
+  name = Applicable 3
+
+{
+   "applicable" : true,
+   "hasPass" : false,
+   "name" : "Root branch applicable Property",
+   "status" : "WAITING",
+   "subTasks" : [
+      {
+         "applicable" : true,
+         "hasPass" : true,
+         "name" : "Applicable 1",
+         "status" : "FAIL"
+      },
+      {
+         "applicable" : true,
+         "hasPass" : true,
+         "name" : "Applicable 2",
+         "status" : "FAIL"
+      },
+      {
+         "applicable" : true,
+         "hasPass" : true,
+         "name" : "Applicable 3",
+         "status" : "FAIL"
+      }
+   ]
+}
+
 [root "Root Properties tasks-factory STATIC"]
   subtasks-factory = tasks-factory STATIC Properties
 
@@ -1393,6 +1486,46 @@
    ]
 }
 
+[root "Root CHANGE constant subtask list CHANGE Properties"]
+  subtasks-factory = tasks-factory Properties CHANGE names-factory CHANGE
+
+[tasks-factory "tasks-factory Properties CHANGE names-factory CHANGE"]
+  names-factory = Properties names-factory current CHANGE
+  subtask = Current CHANGE Property
+
+[task "Current CHANGE Property"]
+  fail = True
+  fail-hint = Current Change: ${_change_number}
+
+[names-factory "Properties names-factory current CHANGE"]
+  type = change
+  changes = change:${_change_number}
+
+{
+   "applicable" : true,
+   "hasPass" : false,
+   "name" : "Root CHANGE constant subtask list CHANGE Properties",
+   "status" : "WAITING",
+   "subTasks" : [
+      {
+         "applicable" : true,
+         "change" : _change_number,
+         "hasPass" : false,
+         "name" : "_change_number",
+         "status" : "WAITING",
+         "subTasks" : [
+            {
+               "applicable" : true,
+               "hasPass" : true,
+               "hint" : "Current Change: _change_number",
+               "name" : "Current CHANGE Property",
+               "status" : "FAIL"
+            }
+         ]
+      }
+   ]
+}
+
 [root "Root Preload"]
    preload-task = Subtask FAIL
    subtask = Subtask Preload
@@ -1814,6 +1947,213 @@
    ]
 }
 
+[root "Root Looping"]
+  subtask = Looping
+
+[task "Looping"]
+  subtask = Looping
+  pass = True
+
+{
+   "applicable" : true,
+   "hasPass" : false,
+   "name" : "Root Looping",
+   "status" : "PASS",
+   "subTasks" : [
+      {
+         "applicable" : true,
+         "hasPass" : true,
+         "name" : "Looping",
+         "status" : "PASS",
+         "subTasks" : [
+            {
+               "applicable" : true,
+               "hasPass" : false,
+               "hint" : "Duplicate task is non blocking and empty to break the loop",
+               "name" : "Looping",
+               "status" : "DUPLICATE"
+            }
+         ]
+      }
+   ]
+}
+
+[root "Root Looping DuplicateKey"]
+  preload-task = DuplicateKey
+
+[task "Looping DuplicateKey"]
+  preload-task = DuplicateKey
+  pass = True
+
+[task "DuplicateKey"]
+  duplicate-key = 1234
+  subtask = Looping DuplicateKey
+
+
+{
+   "applicable" : true,
+   "hasPass" : false,
+   "name" : "Root Looping DuplicateKey",
+   "status" : "PASS",
+   "subTasks" : [
+      {
+         "applicable" : true,
+         "hasPass" : false,
+         "hint" : "Duplicate task is non blocking and empty to break the loop",
+         "name" : "Looping DuplicateKey",
+         "status" : "DUPLICATE"
+      }
+   ]
+}
+
+[root "Root changes loop"]
+  subtask = task (tasks-factory changes loop)
+
+[task "task (tasks-factory changes loop)"]
+  subtasks-factory = tasks-factory change loop
+
+[tasks-factory "tasks-factory change loop"]
+  names-factory = names-factory change constant
+  subtask = task (tasks-factory changes loop)
+  fail = True
+
+[names-factory "names-factory change constant"]
+  changes = change:_change1_number OR change:_change2_number
+  type = change
+
+{
+   "applicable" : true,
+   "hasPass" : false,
+   "name" : "Root changes loop",
+   "status" : "WAITING",
+   "subTasks" : [
+      {
+         "applicable" : true,
+         "hasPass" : false,
+         "name" : "task (tasks-factory changes loop)",
+         "status" : "WAITING",
+         "subTasks" : [
+            {
+               "applicable" : true,
+               "change" : _change1_number,
+               "hasPass" : true,
+               "name" : "_change1_number",
+               "status" : "FAIL",
+               "subTasks" : [
+                  {
+                     "applicable" : true,
+                     "hasPass" : false,
+                     "name" : "task (tasks-factory changes loop)",
+                     "status" : "WAITING",
+                     "subTasks" : [
+                        {
+                           "applicable" : true,
+                           "change" : _change1_number,
+                           "hasPass" : false,
+                           "hint" : "Duplicate task is non blocking and empty to break the loop",
+                           "name" : "_change1_number",
+                           "status" : "DUPLICATE"
+                        },
+                        {
+                           "applicable" : true,
+                           "change" : _change2_number,
+                           "hasPass" : true,
+                           "name" : "_change2_number",
+                           "status" : "FAIL",
+                           "subTasks" : [
+                              {
+                                 "applicable" : true,
+                                 "hasPass" : false,
+                                 "name" : "task (tasks-factory changes loop)",
+                                 "status" : "PASS",
+                                 "subTasks" : [
+                                    {
+                                       "applicable" : true,
+                                       "change" : _change1_number,
+                                       "hasPass" : false,
+                                       "hint" : "Duplicate task is non blocking and empty to break the loop",
+                                       "name" : "_change1_number",
+                                       "status" : "DUPLICATE"
+                                    },
+                                    {
+                                       "applicable" : true,
+                                       "change" : _change2_number,
+                                       "hasPass" : false,
+                                       "hint" : "Duplicate task is non blocking and empty to break the loop",
+                                       "name" : "_change2_number",
+                                       "status" : "DUPLICATE"
+                                    }
+                                 ]
+                              }
+                           ]
+                        }
+                     ]
+                  }
+               ]
+            },
+            {
+               "applicable" : true,
+               "change" : _change2_number,
+               "hasPass" : true,
+               "name" : "_change2_number",
+               "status" : "FAIL",
+               "subTasks" : [
+                  {
+                     "applicable" : true,
+                     "hasPass" : false,
+                     "name" : "task (tasks-factory changes loop)",
+                     "status" : "WAITING",
+                     "subTasks" : [
+                        {
+                           "applicable" : true,
+                           "change" : _change1_number,
+                           "hasPass" : true,
+                           "name" : "_change1_number",
+                           "status" : "FAIL",
+                           "subTasks" : [
+                              {
+                                 "applicable" : true,
+                                 "hasPass" : false,
+                                 "name" : "task (tasks-factory changes loop)",
+                                 "status" : "PASS",
+                                 "subTasks" : [
+                                    {
+                                       "applicable" : true,
+                                       "change" : _change1_number,
+                                       "hasPass" : false,
+                                       "hint" : "Duplicate task is non blocking and empty to break the loop",
+                                       "name" : "_change1_number",
+                                       "status" : "DUPLICATE"
+                                    },
+                                    {
+                                       "applicable" : true,
+                                       "change" : _change2_number,
+                                       "hasPass" : false,
+                                       "hint" : "Duplicate task is non blocking and empty to break the loop",
+                                       "name" : "_change2_number",
+                                       "status" : "DUPLICATE"
+                                    }
+                                 ]
+                              }
+                           ]
+                        },
+                        {
+                           "applicable" : true,
+                           "change" : _change2_number,
+                           "hasPass" : false,
+                           "hint" : "Duplicate task is non blocking and empty to break the loop",
+                           "name" : "_change2_number",
+                           "status" : "DUPLICATE"
+                        }
+                     ]
+                  }
+               ]
+            }
+         ]
+      }
+   ]
+}
+
 [root "Root INVALID Preload"]
   preload-task = missing
 
@@ -1946,18 +2286,6 @@
          "status" : "INVALID"   # Only Test Suite: !all
       },
       {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "Looping",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "name" : "UNKNOWN",
-               "status" : "INVALID"
-            }
-         ]
-      },
-      {
          "name" : "UNKNOWN",
          "status" : "INVALID"
       },
@@ -2050,106 +2378,6 @@
                "status" : "INVALID"
             }
          ]
-      },
-      {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "task (tasks-factory changes loop)",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "applicable" : true,
-               "change" : _change1_number,
-               "hasPass" : true,
-               "name" : "_change1_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        },
-                        {
-                           "applicable" : true,
-                           "change" : _change2_number,
-                           "hasPass" : true,
-                           "name" : "_change2_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        }
-                     ]
-                  }
-               ]
-            },
-            {
-               "applicable" : true,
-               "change" : _change2_number,
-               "hasPass" : true,
-               "name" : "_change2_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "applicable" : true,
-                           "change" : _change1_number,
-                           "hasPass" : true,
-                           "name" : "_change1_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        },
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        }
-                     ]
-                  }
-               ]
-            }
-         ]
       }
    ]
 }
@@ -2301,18 +2529,6 @@
          "status" : "INVALID"   # Only Test Suite: !all
       },
       {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "Looping",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "name" : "UNKNOWN",
-               "status" : "INVALID"
-            }
-         ]
-      },
-      {
          "name" : "UNKNOWN",
          "status" : "INVALID"
       },
@@ -2405,106 +2621,6 @@
                "status" : "INVALID"
             }
          ]
-      },
-      {
-         "applicable" : true,
-         "hasPass" : false,
-         "name" : "task (tasks-factory changes loop)",
-         "status" : "WAITING",
-         "subTasks" : [
-            {
-               "applicable" : true,
-               "change" : _change1_number,
-               "hasPass" : true,
-               "name" : "_change1_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        },
-                        {
-                           "applicable" : true,
-                           "change" : _change2_number,
-                           "hasPass" : true,
-                           "name" : "_change2_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        }
-                     ]
-                  }
-               ]
-            },
-            {
-               "applicable" : true,
-               "change" : _change2_number,
-               "hasPass" : true,
-               "name" : "_change2_number",
-               "status" : "FAIL",
-               "subTasks" : [
-                  {
-                     "applicable" : true,
-                     "hasPass" : false,
-                     "name" : "task (tasks-factory changes loop)",
-                     "status" : "WAITING",
-                     "subTasks" : [
-                        {
-                           "applicable" : true,
-                           "change" : _change1_number,
-                           "hasPass" : true,
-                           "name" : "_change1_number",
-                           "status" : "FAIL",
-                           "subTasks" : [
-                              {
-                                 "applicable" : true,
-                                 "hasPass" : false,
-                                 "name" : "task (tasks-factory changes loop)",
-                                 "status" : "WAITING",
-                                 "subTasks" : [
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    },
-                                    {
-                                       "name" : "UNKNOWN",
-                                       "status" : "INVALID"
-                                    }
-                                 ]
-                              }
-                           ]
-                        },
-                        {
-                           "name" : "UNKNOWN",
-                           "status" : "INVALID"
-                        }
-                     ]
-                  }
-               ]
-            }
-         ]
       }
    ]
 }
@@ -2568,9 +2684,6 @@
   fail = True
   in-progress = has:bad
 
-[task "Looping"]
-  subtask = Looping
-
 [task "Looping Properties"]
   set-A = ${B}
   set-B = ${A}
@@ -2598,9 +2711,6 @@
 [task "task (names-factory changes invalid)"]
   subtasks-factory = tasks-factory change (names-factory changes invalid)
 
-[task "task (tasks-factory changes loop)"]
-  subtasks-factory = tasks-factory change loop
-
 [tasks-factory "tasks-factory (names-factory type missing)"]
   names-factory = names-factory (type missing)
   fail = True
@@ -2624,11 +2734,6 @@
   names-factory = names-factory change list (changes invalid)
   fail = True
 
-[tasks-factory "tasks-factory change loop"]
-  names-factory = names-factory change constant
-  subtask = task (tasks-factory changes loop)
-  fail = True
-
 [names-factory "names-factory (type missing)"]
   name = no type test
 
@@ -2648,11 +2753,7 @@
   type = change
 
 [names-factory "names-factory change list (changes invalid)"]
-  change = change:invalidChange
-  type = change
-
-[names-factory "names-factory change constant"]
-  changes = change:_change1_number OR change:_change2_number
+  changes = change:invalidChange
   type = change
 
 ```
diff --git a/src/test/java/com/googlesource/gerrit/plugins/task/TaskExpressionTest.java b/src/test/java/com/googlesource/gerrit/plugins/task/TaskExpressionTest.java
index 1bece85..2f27439 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/task/TaskExpressionTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/task/TaskExpressionTest.java
@@ -34,107 +34,111 @@
   public static String PEACE = "peace";
   public static FileKey file = createFileKey("foo", "bar", "baz");
 
+  public static TaskKey SIMPLE_TASK = TaskKey.create(file, SIMPLE);
+  public static TaskKey WORLD_TASK = TaskKey.create(file, WORLD);
+  public static TaskKey PEACE_TASK = TaskKey.create(file, PEACE);
+
   public void testBlank() {
     TaskExpression exp = getTaskExpression("");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
     assertNoSuchElementException(it);
   }
 
   public void testRequiredSingleName() {
     TaskExpression exp = getTaskExpression(SIMPLE);
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), SIMPLE);
+    assertEquals(it.next(), SIMPLE_TASK);
     assertTrue(it.hasNext());
     assertNoSuchElementException(it);
   }
 
   public void testOptionalSingleName() {
     TaskExpression exp = getTaskExpression(SIMPLE + "|");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), SIMPLE);
+    assertEquals(it.next(), SIMPLE_TASK);
     assertFalse(it.hasNext());
   }
 
   public void testRequiredTwoNames() {
     TaskExpression exp = getTaskExpression(WORLD + "|" + PEACE);
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), WORLD);
+    assertEquals(it.next(), WORLD_TASK);
     assertTrue(it.hasNext());
-    assertEquals(it.next(), PEACE);
+    assertEquals(it.next(), PEACE_TASK);
     assertTrue(it.hasNext());
     assertNoSuchElementException(it);
   }
 
   public void testOptionalTwoNames() {
     TaskExpression exp = getTaskExpression(WORLD + "|" + PEACE + "|");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), WORLD);
+    assertEquals(it.next(), WORLD_TASK);
     assertTrue(it.hasNext());
-    assertEquals(it.next(), PEACE);
+    assertEquals(it.next(), PEACE_TASK);
     assertFalse(it.hasNext());
   }
 
   public void testBlankSpaces() {
     TaskExpression exp = getTaskExpression("  ");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
     assertNoSuchElementException(it);
   }
 
   public void testRequiredSingleNameLeadingSpaces() {
     TaskExpression exp = getTaskExpression("  " + SIMPLE);
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), SIMPLE);
+    assertEquals(it.next(), SIMPLE_TASK);
     assertTrue(it.hasNext());
     assertNoSuchElementException(it);
   }
 
   public void testRequiredSingleNameTrailingSpaces() {
     TaskExpression exp = getTaskExpression(SIMPLE + "  ");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), SIMPLE);
+    assertEquals(it.next(), SIMPLE_TASK);
     assertTrue(it.hasNext());
     assertNoSuchElementException(it);
   }
 
   public void testOptionalSingleNameLeadingSpaces() {
     TaskExpression exp = getTaskExpression("  " + SIMPLE + "|");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), SIMPLE);
+    assertEquals(it.next(), SIMPLE_TASK);
     assertFalse(it.hasNext());
   }
 
   public void testOptionalSingleNameTrailingSpaces() {
     TaskExpression exp = getTaskExpression(SIMPLE + "|  ");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), SIMPLE);
+    assertEquals(it.next(), SIMPLE_TASK);
     assertFalse(it.hasNext());
   }
 
   public void testOptionalSingleNameMiddleSpaces() {
     TaskExpression exp = getTaskExpression(SIMPLE + "  |");
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), SIMPLE);
+    assertEquals(it.next(), SIMPLE_TASK);
     assertFalse(it.hasNext());
   }
 
   public void testRequiredTwoNamesMiddleSpaces() {
     TaskExpression exp = getTaskExpression(WORLD + "  |  " + PEACE);
-    Iterator<String> it = exp.iterator();
+    Iterator<TaskKey> it = exp.iterator();
     assertTrue(it.hasNext());
-    assertEquals(it.next(), WORLD);
+    assertEquals(it.next(), WORLD_TASK);
     assertTrue(it.hasNext());
-    assertEquals(it.next(), PEACE);
+    assertEquals(it.next(), PEACE_TASK);
     assertTrue(it.hasNext());
     assertNoSuchElementException(it);
   }
@@ -163,7 +167,7 @@
     assertFalse(exp.key.equals(otherExp.key));
   }
 
-  protected static void assertNoSuchElementException(Iterator<String> it) {
+  protected static void assertNoSuchElementException(Iterator<TaskKey> it) {
     try {
       it.next();
       assertTrue(false);
diff --git a/test/strip_non_applicable.py b/test/strip_non_applicable.py
index 1ff097a..41c21fa 100755
--- a/test/strip_non_applicable.py
+++ b/test/strip_non_applicable.py
@@ -43,7 +43,7 @@
                     status=''
                     if STATUS in task.keys():
                         status = task[STATUS]
-                    if status != 'INVALID':
+                    if status != 'INVALID' and status != 'DUPLICATE':
                         del tasks[i]
                         nexti = i
 
diff --git a/tools/playbooks/install_python3-distutils.yaml b/tools/playbooks/install_python3-distutils.yaml
new file mode 100644
index 0000000..75f5a2a
--- /dev/null
+++ b/tools/playbooks/install_python3-distutils.yaml
@@ -0,0 +1,10 @@
+- hosts: all
+  roles:
+    - name: ensure-python
+  tasks:
+    - name: Install python3-distutils
+      become: true
+      package:
+        name:
+          - python3-distutils
+        state: present