Allow plugins to output change query attributes

Create a ChangeAttributeFactory interface to allow
plugins to register to provide additonal attributes to be
output in a change query result.

Example Usage:
    https://gerrit-review.googlesource.com/#/c/102650/

Change-Id: I4a09d9abd8bda09a3ecde7ca203434d6ab8ab7be

Documentation/dev-plugins.txt

@@ -736,6 +736,68 @@ public class SshModule extends AbstractModule {
   }
 ----
 
+[[query_attributes]]
+=== Query Attributes ===
+
+Plugins can provide additional attributes to be returned in Gerrit queries by
+implementing the ChangeAttributeFactory interface and registering it to the
+ChangeQueryProcessor.ChangeAttributeFactory class in the plugin module's
+'configure()' method. The new attribute(s) will be output under a "plugin"
+attribute in the change query output.
+
+The example below shows a plugin that adds two attributes ('exampleName' and
+'changeValue'), to the change query output.
+
+[source, java]
+----
+public class Module extends AbstractModule {
+  @Override
+  protected void configure() {
+    bind(ChangeAttributeFactory.class)
+        .annotatedWith(Exports.named("example"))
+        .to(AttributeFactory.class);
+  }
+}
+
+public class AttributeFactory implements ChangeAttributeFactory {
+
+  public class PluginAttribute extends PluginDefinedInfo {
+    public String exampleName;
+    public String changeValue;
+
+    public PluginAttribute(ChangeData c) {
+      this.exampleName = "Attribute Example";
+      this.changeValue = Integer.toString(c.getId().get());
+    }
+  }
+
+  @Override
+  public PluginDefinedInfo create(ChangeData c, ChangeQueryProcessor qp, String plugin) {
+    return new PluginAttribute(c);
+  }
+}
+----
+
+Example
+----
+
+ssh -p 29418 localhost gerrit query "change:1" --format json
+
+Output:
+
+{
+   "url" : "http://localhost:8080/1",
+   "plugins" : [
+      {
+         "name" : "myplugin-name",
+         "exampleName" : "Attribute Example",
+         "changeValue" : "1"
+      }
+   ],
+    ...
+}
+----
+
 [[simple-configuration]]
 == Simple Configuration in `gerrit.config`
 

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/common/ChangeInfo.java

@@ -63,4 +63,5 @@ public class ChangeInfo {
   public Boolean _moreChanges;
 
   public List<ProblemInfo> problems;
+  public List<PluginDefinedInfo> plugins;
 }

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/common/PluginDefinedInfo.java

@@ -0,0 +1,19 @@
+// Copyright (C) 2017 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.google.gerrit.extensions.common;
+
+public class PluginDefinedInfo {
+  public String name;
+}

gerrit-pgm/src/main/java/com/google/gerrit/pgm/util/BatchProgramModule.java

@@ -68,6 +68,7 @@ import com.google.gerrit.server.project.ProjectCacheImpl;
 import com.google.gerrit.server.project.ProjectState;
 import com.google.gerrit.server.project.SectionSortCache;
 import com.google.gerrit.server.query.change.ChangeData;
+import com.google.gerrit.server.query.change.ChangeQueryProcessor;
 import com.google.gerrit.server.update.BatchUpdate;
 import com.google.inject.Inject;
 import com.google.inject.Module;
@@ -112,6 +113,8 @@ public class BatchProgramModule extends FactoryModule {
     bind(new TypeLiteral<List<CommentLinkInfo>>() {})
         .toProvider(CommentLinkProvider.class)
         .in(SINGLETON);
+    bind(new TypeLiteral<DynamicMap<ChangeQueryProcessor.ChangeAttributeFactory>>() {})
+        .toInstance(DynamicMap.<ChangeQueryProcessor.ChangeAttributeFactory>emptyMap());
     bind(String.class)
         .annotatedWith(CanonicalWebUrl.class)
         .toProvider(CanonicalWebUrlProvider.class);

gerrit-server/src/main/java/com/google/gerrit/server/change/ChangeJson.java

@@ -118,6 +118,7 @@ import com.google.gerrit.server.project.SubmitRuleOptions;
 import com.google.gerrit.server.query.QueryResult;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.gerrit.server.query.change.ChangeData.ChangedLines;
+import com.google.gerrit.server.query.change.PluginDefinedAttributesFactory;
 import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
@@ -213,6 +214,7 @@ public class ChangeJson {
   private boolean lazyLoad = true;
   private AccountLoader accountLoader;
   private FixInput fix;
+  private PluginDefinedAttributesFactory pluginDefinedAttributesFactory;
 
   @Inject
   ChangeJson(
@@ -276,6 +278,10 @@ public class ChangeJson {
     return this;
   }
 
+  public void setPluginDefinedAttributesFactory(PluginDefinedAttributesFactory pluginsFactory) {
+    this.pluginDefinedAttributesFactory = pluginsFactory;
+  }
+
   public ChangeInfo format(ChangeResource rsrc) throws OrmException {
     return format(changeDataFactory.create(db.get(), rsrc.getControl()));
   }
@@ -516,6 +522,8 @@ public class ChangeJson {
 
     out.labels = labelsFor(ctl, cd, has(LABELS), has(DETAILED_LABELS));
     out.submitted = getSubmittedOn(cd);
+    out.plugins =
+        pluginDefinedAttributesFactory != null ? pluginDefinedAttributesFactory.create(cd) : null;
 
     if (out.labels != null && has(DETAILED_LABELS)) {
       // If limited to specific patch sets but not the current patch set, don't

gerrit-server/src/main/java/com/google/gerrit/server/config/GerritGlobalModule.java

@@ -166,6 +166,7 @@ import com.google.gerrit.server.project.ProjectState;
 import com.google.gerrit.server.project.SectionSortCache;
 import com.google.gerrit.server.query.change.ChangeData;
 import com.google.gerrit.server.query.change.ChangeQueryBuilder;
+import com.google.gerrit.server.query.change.ChangeQueryProcessor;
 import com.google.gerrit.server.query.change.ConflictsCacheImpl;
 import com.google.gerrit.server.ssh.SshAddressesModule;
 import com.google.gerrit.server.tools.ToolsCatalog;
@@ -378,6 +379,8 @@ public class GerritGlobalModule extends FactoryModule {
 
     DynamicMap.mapOf(binder(), ChangeQueryBuilder.ChangeOperatorFactory.class);
     DynamicMap.mapOf(binder(), ChangeQueryBuilder.ChangeHasOperandFactory.class);
+    DynamicMap.mapOf(binder(), ChangeQueryProcessor.ChangeAttributeFactory.class);
+
     install(new GitwebConfig.LegacyModule(cfg));
 
     bind(AnonymousUser.class);

gerrit-server/src/main/java/com/google/gerrit/server/data/ChangeAttribute.java

@@ -14,6 +14,7 @@
 
 package com.google.gerrit.server.data;
 
+import com.google.gerrit.extensions.common.PluginDefinedInfo;
 import com.google.gerrit.reviewdb.client.Change;
 import java.util.List;
 
@@ -43,4 +44,5 @@ public class ChangeAttribute {
   public List<DependencyAttribute> neededBy;
   public List<SubmitRecordAttribute> submitRecords;
   public List<AccountAttribute> allReviewers;
+  public List<PluginDefinedInfo> plugins;
 }

gerrit-server/src/main/java/com/google/gerrit/server/query/change/ChangeQueryProcessor.java

@@ -17,6 +17,8 @@ package com.google.gerrit.server.query.change;
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.gerrit.server.query.change.ChangeQueryBuilder.FIELD_LIMIT;
 
+import com.google.gerrit.extensions.common.PluginDefinedInfo;
+import com.google.gerrit.extensions.registration.DynamicMap;
 import com.google.gerrit.reviewdb.server.ReviewDb;
 import com.google.gerrit.server.CurrentUser;
 import com.google.gerrit.server.index.IndexConfig;
@@ -32,12 +34,26 @@ import com.google.gerrit.server.query.Predicate;
 import com.google.gerrit.server.query.QueryProcessor;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Set;
 
-public class ChangeQueryProcessor extends QueryProcessor<ChangeData> {
+public class ChangeQueryProcessor extends QueryProcessor<ChangeData>
+    implements PluginDefinedAttributesFactory {
+  /**
+   * Register a ChangeAttributeFactory in a config Module like this:
+   *
+   * <p>bind(ChangeAttributeFactory.class) .annotatedWith(Exports.named("export-name"))
+   * .to(YourClass.class);
+   */
+  public interface ChangeAttributeFactory {
+    PluginDefinedInfo create(ChangeData a, ChangeQueryProcessor qp, String plugin);
+  }
+
   private final Provider<ReviewDb> db;
   private final ChangeControl.GenericFactory changeControlFactory;
   private final ChangeNotes.Factory notesFactory;
+  private final DynamicMap<ChangeAttributeFactory> attributeFactories;
 
   static {
     // It is assumed that basic rewrites do not touch visibleto predicates.
@@ -55,7 +71,8 @@ public class ChangeQueryProcessor extends QueryProcessor<ChangeData> {
       ChangeIndexRewriter rewriter,
       Provider<ReviewDb> db,
       ChangeControl.GenericFactory changeControlFactory,
-      ChangeNotes.Factory notesFactory) {
+      ChangeNotes.Factory notesFactory,
+      DynamicMap<ChangeAttributeFactory> attributeFactories) {
     super(
         userProvider,
         metrics,
@@ -67,6 +84,7 @@ public class ChangeQueryProcessor extends QueryProcessor<ChangeData> {
     this.db = db;
     this.changeControlFactory = changeControlFactory;
     this.notesFactory = notesFactory;
+    this.attributeFactories = attributeFactories;
   }
 
   @Override
@@ -81,6 +99,30 @@ public class ChangeQueryProcessor extends QueryProcessor<ChangeData> {
     return IndexedChangeQuery.createOptions(indexConfig, start, limit, requestedFields);
   }
 
+  @Override
+  public List<PluginDefinedInfo> create(ChangeData cd) {
+    List<PluginDefinedInfo> plugins = new ArrayList<>(attributeFactories.plugins().size());
+    for (String plugin : attributeFactories.plugins()) {
+      for (Provider<ChangeAttributeFactory> provider :
+          attributeFactories.byPlugin(plugin).values()) {
+        PluginDefinedInfo pda = null;
+        try {
+          pda = provider.get().create(cd, this, plugin);
+        } catch (RuntimeException e) {
+          /* Eat runtime exceptions so that queries don't fail. */
+        }
+        if (pda != null) {
+          pda.name = plugin;
+          plugins.add(pda);
+        }
+      }
+    }
+    if (plugins.isEmpty()) {
+      plugins = null;
+    }
+    return plugins;
+  }
+
   @Override
   protected Predicate<ChangeData> enforceVisibility(Predicate<ChangeData> pred) {
     return new AndChangeSource(

gerrit-server/src/main/java/com/google/gerrit/server/query/change/OutputStreamQuery.java

@@ -313,6 +313,7 @@ public class OutputStreamQuery {
       eventFactory.addDependencies(rw, c, d.change(), d.currentPatchSet());
     }
 
+    c.plugins = queryProcessor.create(d);
     return c;
   }
 

gerrit-server/src/main/java/com/google/gerrit/server/query/change/PluginDefinedAttributesFactory.java

@@ -0,0 +1,22 @@
+// Copyright (C) 2016 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.google.gerrit.server.query.change;
+
+import com.google.gerrit.extensions.common.PluginDefinedInfo;
+import java.util.List;
+
+public interface PluginDefinedAttributesFactory {
+  List<PluginDefinedInfo> create(ChangeData cd);
+}

gerrit-server/src/main/java/com/google/gerrit/server/query/change/QueryChanges.java

@@ -137,13 +137,18 @@ public class QueryChanges implements RestReadView<TopLevelResource> {
 
     int cnt = queries.size();
     List<QueryResult<ChangeData>> results = imp.query(qb.parse(queries));
+
     boolean requireLazyLoad =
         containsAnyOf(options, ImmutableSet.of(DETAILED_LABELS, LABELS))
             && !qb.getArgs().getSchema().hasField(ChangeField.STORED_SUBMIT_RECORD_LENIENT);
+
+    ChangeJson cjson = json.create(options);
+    cjson.setPluginDefinedAttributesFactory(this.imp);
     List<List<ChangeInfo>> res =
-        json.create(options)
+        cjson
             .lazyLoad(requireLazyLoad || containsAnyOf(options, ChangeJson.REQUIRE_LAZY_LOAD))
             .formatQueryResults(results);
+
     for (int n = 0; n < cnt; n++) {
       List<ChangeInfo> info = res.get(n);
       if (results.get(n).more()) {

gerrit-sshd/src/main/java/com/google/gerrit/sshd/commands/Query.java

@@ -24,7 +24,7 @@ import org.kohsuke.args4j.Argument;
 import org.kohsuke.args4j.Option;
 
 @CommandMetaData(name = "query", description = "Query the change database")
-class Query extends SshCommand {
+public class Query extends SshCommand {
   @Inject private OutputStreamQuery processor;
 
   @Option(name = "--format", metaVar = "FMT", usage = "Output display format")