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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.
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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * 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.javascript.jscomp.instrumentation;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.javascript.jscomp.AbstractCompiler;
import com.google.javascript.jscomp.ControlFlowGraph;
import com.google.javascript.jscomp.NodeTraversal;
import com.google.javascript.jscomp.NodeUtil;
import com.google.javascript.jscomp.graph.DiGraph;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Objects;

/** Instrument branch coverage for javascript. */
@GwtIncompatible("FileInstrumentationData")
public class BranchCoverageInstrumentationCallback extends NodeTraversal.AbstractCfgCallback {
  private final AbstractCompiler compiler;
  private final Map instrumentationData;

  private static final String BRANCH_ARRAY_NAME_PREFIX = "JSCompiler_lcov_branch_data_";

  /** Returns a string that can be used for the branch coverage data. */
  private static String createArrayName(NodeTraversal traversal) {
    return BRANCH_ARRAY_NAME_PREFIX
        + CoverageUtil.createIdentifierFromText(traversal.getSourceName());
  }

  public BranchCoverageInstrumentationCallback(
      AbstractCompiler compiler, Map instrumentationData) {
    this.compiler = compiler;
    this.instrumentationData = instrumentationData;
  }

  @Override
  public void visit(NodeTraversal traversal, Node node, Node parent) {
    String fileName = traversal.getSourceName();

    // If origin of node is not from sourceFile, do not instrument. This typically occurs when
    // polyfill code is injected into the sourceFile AST and this check avoids instrumenting it. We
    // avoid instrumentation as this callback does not distinguish between sourceFile code and
    // injected code and can result in an error.
    if (!Objects.equals(fileName, node.getSourceFileName())) {
      return;
    }

    if (node.isScript()) {
      if (instrumentationData.get(fileName) != null) {
        Node toAddTo =
            node.hasChildren() && node.getFirstChild().isModuleBody() ? node.getFirstChild() : node;
        // Add instrumentation code
        toAddTo.addChildrenToFront(newHeaderNode(traversal, toAddTo).removeChildren());
        compiler.reportChangeToEnclosingScope(node);
        instrumentBranchCoverage(traversal, instrumentationData.get(fileName));
      }
    }

    if (node.isIf()) {
      ControlFlowGraph cfg = getControlFlowGraph(compiler);
      boolean hasDefaultBlock = false;
      for (DiGraph.DiGraphEdge outEdge : cfg.getOutEdges(node)) {
        if (outEdge.getValue() == ControlFlowGraph.Branch.ON_FALSE) {
          Node destination = outEdge.getDestination().getValue();
          if (destination != null
              && destination.isBlock()
              && destination.getParent() != null
              && destination.getParent().isIf()) {
            hasDefaultBlock = true;
          }
          break;
        }
      }
      if (!hasDefaultBlock) {
        addDefaultBlock(node);
      }
      instrumentationData.computeIfAbsent(
          fileName, (String k) -> new FileInstrumentationData(k, createArrayName(traversal)));
      processBranchInfo(node, instrumentationData.get(fileName), getChildrenBlocks(node));
    } else if (NodeUtil.isLoopStructure(node)) {
      List blocks = getChildrenBlocks(node);
      ControlFlowGraph cfg = getControlFlowGraph(compiler);
      for (DiGraph.DiGraphEdge outEdge : cfg.getOutEdges(node)) {
        if (outEdge.getValue() == ControlFlowGraph.Branch.ON_FALSE) {
          Node destination = outEdge.getDestination().getValue();
          if (destination != null && destination.isBlock()) {
            blocks.add(destination);
          } else {
            Node exitBlock = IR.block();
            if (destination != null && destination.getParent().isBlock()) {
              // When the destination of an outEdge of the CFG is not null and the source node's
              // parent is a block. If parent is not a block it may result in an illegal state
              // exception
              exitBlock.insertBefore(destination);
            } else {
              // When the destination of an outEdge of the CFG is null then we need to add an empty
              // block directly after the loop structure that we can later instrument
              exitBlock.insertAfter(outEdge.getSource().getValue());
            }
            blocks.add(exitBlock);
          }
        }
      }
      instrumentationData.computeIfAbsent(
          fileName, (String k) -> new FileInstrumentationData(k, createArrayName(traversal)));
      processBranchInfo(node, instrumentationData.get(fileName), blocks);
    }
  }

  private List getChildrenBlocks(Node node) {
    List blocks = new ArrayList<>();
    for (Node child = node.getFirstChild(); child != null; child = child.getNext()) {
      if (child.isBlock()) {
        blocks.add(child);
      }
    }
    return blocks;
  }

  /**
   * Add instrumentation code for branch coverage. For each block that correspond to a branch,
   * insert an assignment of the branch coverage data to the front of the block.
   */
  private void instrumentBranchCoverage(NodeTraversal traversal, FileInstrumentationData data) {
    int maxLine = data.maxBranchPresentLine();
    int branchCoverageOffset = 0;
    for (int lineIdx = 1; lineIdx <= maxLine; ++lineIdx) {
      Integer numBranches = data.getNumBranches(lineIdx);
      if (numBranches != null) {
        for (int branchIdx = 1; branchIdx <= numBranches; ++branchIdx) {
          Node block = data.getBranchNode(lineIdx, branchIdx);
          block.addChildToFront(
              newBranchInstrumentationNode(traversal, block, branchCoverageOffset + branchIdx - 1));
          compiler.reportChangeToEnclosingScope(block);
        }
        branchCoverageOffset += numBranches;
      }
    }
  }

  /**
   * Create an assignment to the branch coverage data for the given index into the array.
   *
   * @return the newly constructed assignment node.
   */
  private Node newBranchInstrumentationNode(NodeTraversal traversal, Node node, int idx) {
    String arrayName = createArrayName(traversal);

    // Create instrumentation Node
    Node getElemNode = IR.getelem(IR.name(arrayName), IR.number(idx)); // Make line number 0-based
    Node exprNode = IR.exprResult(IR.assign(getElemNode, IR.trueNode()));

    // Note line as instrumented
    String fileName = traversal.getSourceName();
    instrumentationData.computeIfAbsent(
        fileName, (String k) -> new FileInstrumentationData(k, arrayName));
    return exprNode.srcrefTreeIfMissing(node);
  }

  /** Add branch instrumentation information for each block. */
  private void processBranchInfo(Node branchNode, FileInstrumentationData data, List blocks) {
    int lineNumber = branchNode.getLineno();
    data.setBranchPresent(lineNumber);

    // Instrument for each block
    int numBranches = 0;
    for (Node child : blocks) {
      data.putBranchNode(lineNumber, numBranches + 1, child);
      numBranches++;
    }
    data.addBranches(lineNumber, numBranches);
  }

  /** Add a default block for conditional statements, e.g., If, Switch. */
  private Node addDefaultBlock(Node node) {
    Node defaultBlock = IR.block();
    node.addChildToBack(defaultBlock);
    return defaultBlock.srcrefTreeIfMissing(node);
  }

  private Node newHeaderNode(NodeTraversal traversal, Node srcref) {
    String fileName = traversal.getSourceName();
    FileInstrumentationData data = instrumentationData.get(fileName);
    checkNotNull(data);

    // var JSCompiler_lcov_branch_data_xx = [];
    // __jscov['branchesTaken'].push(JSCompiler_lcov_branch_data_xx);
    String objName = CoverageInstrumentationPass.JS_INSTRUMENTATION_OBJECT_NAME;
    List nodes = new ArrayList<>();
    nodes.add(newArrayDeclarationNode(traversal));
    nodes.add(
        IR.exprResult(
            IR.call(
                IR.getprop(IR.getelem(IR.name(objName), IR.string("branchesTaken")), "push"),
                IR.name(createArrayName(traversal)))));
    // __jscov['branchPresent'].push(hex-data);
    nodes.add(
        IR.exprResult(
            IR.call(
                IR.getprop(IR.getelem(IR.name(objName), IR.string("branchPresent")), "push"),
                IR.string(data.getBranchPresentAsHexString()))));
    nodes.add(newBranchesInLineNode("JSCompiler_lcov_branchesInLine", data));
    // __jscov['branchesInLine'].push(JSCompiler_lcov_branchesInLine);
    nodes.add(
        IR.exprResult(
            IR.call(
                IR.getprop(IR.getelem(IR.name(objName), IR.string("branchesInLine")), "push"),
                IR.name("JSCompiler_lcov_branchesInLine"))));
    // __jscov['fileNames'].push(filename);
    nodes.add(
        IR.exprResult(
            IR.call(
                IR.getprop(IR.getelem(IR.name(objName), IR.string("fileNames")), "push"),
                IR.string(fileName))));
    return IR.block(nodes).srcrefTreeIfMissing(srcref);
  }

  private Node newArrayDeclarationNode(NodeTraversal traversal) {
    return IR.var(IR.name(createArrayName(traversal)), IR.arraylit());
  }

  private Node newBranchesInLineNode(String name, FileInstrumentationData data) {
    List assignments = new ArrayList<>();
    // var JSCompiler_lcov_branchesInLine = [];
    assignments.add(IR.var(IR.name(name), IR.arraylit()));
    int lineWithBranch = 0;
    for (int lineIdx = 1; lineIdx <= data.maxBranchPresentLine(); ++lineIdx) {
      Integer numBranches = data.getNumBranches(lineIdx);
      if (numBranches != null && numBranches > 0) {
        // JSCompiler_lcov_branchesInLine[] = 2;
        Node assignment =
            IR.exprResult(
                IR.assign(
                    IR.getelem(IR.name(name), IR.number(lineWithBranch++)),
                    IR.number(numBranches)));
        assignments.add(assignment.srcrefTreeIfMissing(assignment));
      }
    }
    return IR.block(assignments);
  }
}