Implement cquery --output=graph

src/main/java/com/google/devtools/build/lib/query2/common/CommonQueryOptions.java

@@ -49,6 +49,23 @@ public class CommonQueryOptions extends OptionsBase {
               + " with top-level options.")
   public List<String> universeScope;
 
+  @Option(
+      name = "line_terminator_null",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.QUERY,
+      effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
+      help = "Whether each format is terminated with \\0 instead of newline.")
+  public boolean lineTerminatorNull;
+
+  /** Ugly workaround since line terminator option default has to be constant expression. */
+  public String getLineTerminator() {
+    if (lineTerminatorNull) {
+      return "\0";
+    }
+
+    return System.lineSeparator();
+  }
+
   @Option(
       name = "infer_universe_scope",
       defaultValue = "false",
@@ -253,4 +270,30 @@ public AspectResolutionModeConverter() {
               + "precise mode is not completely precise: the decision whether to compute an aspect "
               + "is decided in the analysis phase, which is not run during 'bazel query'.")
   public AspectResolver.Mode aspectDeps;
+
+  ///////////////////////////////////////////////////////////
+  // GRAPH OUTPUT FORMATTER OPTIONS                        //
+  ///////////////////////////////////////////////////////////
+
+  @Option(
+      name = "graph:node_limit",
+      defaultValue = "512",
+      documentationCategory = OptionDocumentationCategory.QUERY,
+      effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
+      help =
+          "The maximum length of the label string for a graph node in the output.  Longer labels"
+              + " will be truncated; -1 means no truncation.  This option is only applicable to"
+              + " --output=graph.")
+  public int graphNodeStringLimit;
+
+  @Option(
+      name = "graph:factored",
+      defaultValue = "true",
+      documentationCategory = OptionDocumentationCategory.QUERY,
+      effectTags = {OptionEffectTag.TERMINAL_OUTPUT},
+      help =
+          "If true, then the graph will be emitted 'factored', i.e. topologically-equivalent nodes "
+              + "will be merged together and their labels concatenated. This option is only "
+              + "applicable to --output=graph.")
+  public boolean graphFactored;
 }

src/main/java/com/google/devtools/build/lib/query2/cquery/ConfiguredTargetQueryEnvironment.java

@@ -252,6 +252,13 @@ private static ImmutableMap<String, BuildConfiguration> getTransitiveConfigurati
             OutputType.JSON),
         new BuildOutputFormatterCallback(
             eventHandler, cqueryOptions, out, skyframeExecutor, accessor),
+        new GraphOutputFormatterCallback(
+            eventHandler,
+            cqueryOptions,
+            out,
+            skyframeExecutor,
+            accessor,
+            ct -> getFwdDeps(ImmutableList.of(ct))),
         new StarlarkOutputFormatterCallback(
             eventHandler, cqueryOptions, out, skyframeExecutor, accessor));
   }

src/main/java/com/google/devtools/build/lib/query2/cquery/GraphOutputFormatterCallback.java

@@ -0,0 +1,115 @@
+// Copyright 2020 The Bazel Authors. All rights reserved.
+//
+// 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.devtools.build.lib.query2.cquery;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.events.ExtendedEventHandler;
+import com.google.devtools.build.lib.graph.Digraph;
+import com.google.devtools.build.lib.graph.Node;
+import com.google.devtools.build.lib.query2.engine.QueryEnvironment.TargetAccessor;
+import com.google.devtools.build.lib.query2.query.output.GraphOutputWriter;
+import com.google.devtools.build.lib.query2.query.output.GraphOutputWriter.NodeReader;
+import com.google.devtools.build.lib.skyframe.SkyframeExecutor;
+import java.io.OutputStream;
+import java.util.Comparator;
+
+/** cquery output formatter that prints the result as factored graph in AT&T GraphViz format. */
+class GraphOutputFormatterCallback extends CqueryThreadsafeCallback {
+  @Override
+  public String getName() {
+    return "graph";
+  }
+
+  /** Interface for finding a configured target's direct dependencies. */
+  @FunctionalInterface
+  public interface DepsRetriever {
+    Iterable<ConfiguredTarget> getDirectDeps(ConfiguredTarget taget) throws InterruptedException;
+  }
+
+  private final DepsRetriever depsRetriever;
+
+  private final GraphOutputWriter.NodeReader<ConfiguredTarget> nodeReader =
+      new NodeReader<ConfiguredTarget>() {
+
+        private final Comparator<ConfiguredTarget> configuredTargetOrdering =
+            (ct1, ct2) -> {
+              // Order graph output first by target label, then by configuration hash.
+              Label label1 = ct1.getLabel();
+              Label label2 = ct2.getLabel();
+              return label1.equals(label2)
+                  ? ct1.getConfigurationChecksum().compareTo(ct2.getConfigurationChecksum())
+                  : label1.compareTo(label2);
+            };
+
+        @Override
+        public String getLabel(Node<ConfiguredTarget> node) {
+          // Node payloads are ConfiguredTargets. Output node labels are target labels + config
+          // hashes.
+          ConfiguredTarget ct = node.getLabel();
+          return String.format(
+              "%s (%s)",
+              ct.getLabel(),
+              shortId(skyframeExecutor.getConfiguration(eventHandler, ct.getConfigurationKey())));
+        }
+
+        @Override
+        public Comparator<ConfiguredTarget> comparator() {
+          return configuredTargetOrdering;
+        }
+      };
+
+  GraphOutputFormatterCallback(
+      ExtendedEventHandler eventHandler,
+      CqueryOptions options,
+      OutputStream out,
+      SkyframeExecutor skyframeExecutor,
+      TargetAccessor<ConfiguredTarget> accessor,
+      DepsRetriever depsRetriever) {
+    super(eventHandler, options, out, skyframeExecutor, accessor);
+    this.depsRetriever = depsRetriever;
+  }
+
+  @Override
+  public void processOutput(Iterable<ConfiguredTarget> partialResult) throws InterruptedException {
+    // Transform the cquery-backed graph into a Digraph to make it suitable for GraphOutputWriter.
+    // Note that this involves an extra iteration over the entire query result subgraph. We could
+    // conceptually merge transformation and output writing into the same iteration if needed.
+    Digraph<ConfiguredTarget> graph = new Digraph<>();
+    ImmutableSet<ConfiguredTarget> allNodes = ImmutableSet.copyOf(partialResult);
+    for (ConfiguredTarget configuredTarget : partialResult) {
+      Node<ConfiguredTarget> node = graph.createNode(configuredTarget);
+      for (ConfiguredTarget dep : depsRetriever.getDirectDeps(configuredTarget)) {
+        if (allNodes.contains(dep)) {
+          Node<ConfiguredTarget> depNode = graph.createNode(dep);
+          graph.addEdge(node, depNode);
+        }
+      }
+    }
+
+    GraphOutputWriter<ConfiguredTarget> graphWriter =
+        new GraphOutputWriter<>(
+            nodeReader,
+            options.getLineTerminator(),
+            /*sortLabels=*/ true,
+            options.graphNodeStringLimit,
+            // select() conditions don't matter for cquery because cquery operates post-analysis
+            // phase, when select()s have been resolved and removed from the graph.
+            /*maxConditionalEdges=*/ 0,
+            options.graphFactored);
+    graphWriter.write(graph, /*conditionalEdges=*/ null, outputStream);
+  }
+}