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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 2011 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;

import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;

/**
 * Compiler pass that converts all calls to:
 *   goog.object.create(key1, val1, key2, val2, ...) where all of the keys
 *   are literals into object literals.
 *
 * @author [email protected] (Andrew Grieve)
 */
final class ClosureOptimizePrimitives implements CompilerPass {

  /** Reference to the JS compiler */
  private final AbstractCompiler compiler;

  /**
   * Identifies all calls to goog.object.create.
   */
  private class FindObjectCreateCalls extends AbstractPostOrderCallback {

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      if (n.isCall()) {
        Node fn = n.getFirstChild();
        if (fn.matchesQualifiedName("goog$object$create")
            || fn.matchesQualifiedName("goog.object.create")) {
          processObjectCreateCall(n);
        } else if (fn.matchesQualifiedName("goog$object$createSet")
            || fn.matchesQualifiedName("goog.object.createSet")) {
          processObjectCreateSetCall(n);
        }
      }
    }
  }

  /**
   * @param compiler The AbstractCompiler
   */
  ClosureOptimizePrimitives(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    FindObjectCreateCalls pass = new FindObjectCreateCalls();
    NodeTraversal.traverseEs6(compiler, root, pass);
  }

  /**
   * Converts all of the given call nodes to object literals that are safe to
   * do so.
   */
  private void processObjectCreateCall(Node callNode) {
    Node curParam = callNode.getSecondChild();
    if (canOptimizeObjectCreate(curParam)) {
      Node objNode = IR.objectlit().srcref(callNode);
      while (curParam != null) {
        Node keyNode = curParam;
        Node valueNode = curParam.getNext();
        curParam = valueNode.getNext();

        callNode.removeChild(keyNode);
        callNode.removeChild(valueNode);

        if (!keyNode.isString()) {
          keyNode = IR.string(NodeUtil.getStringValue(keyNode))
              .srcref(keyNode);
        }
        keyNode.setType(Token.STRING_KEY);
        keyNode.setQuotedString();
        objNode.addChildToBack(IR.propdef(keyNode, valueNode));
      }
      callNode.getParent().replaceChild(callNode, objNode);
      compiler.reportCodeChange();
    }
  }

  /**
   * Returns whether the given call to goog.object.create can be converted to an
   * object literal.
   */
  private static boolean canOptimizeObjectCreate(Node firstParam) {
    Node curParam = firstParam;
    while (curParam != null) {
      // All keys must be strings or numbers.
      if (!curParam.isString() && !curParam.isNumber()) {
        return false;
      }
      curParam = curParam.getNext();

      // Check for an odd number of parameters.
      if (curParam == null) {
        return false;
      }
      curParam = curParam.getNext();
    }
    return true;
  }

  /**
   * Converts all of the given call nodes to object literals that are safe to
   * do so.
   */
  private void processObjectCreateSetCall(Node callNode) {
    Node curParam = callNode.getSecondChild();
    if (canOptimizeObjectCreateSet(curParam)) {
      Node objNode = IR.objectlit().srcref(callNode);
      while (curParam != null) {
        Node keyNode = curParam;
        Node valueNode = IR.trueNode().srcref(keyNode);

        curParam = curParam.getNext();
        callNode.removeChild(keyNode);

        if (!keyNode.isString()) {
          keyNode = IR.string(NodeUtil.getStringValue(keyNode))
              .srcref(keyNode);
        }
        keyNode.setType(Token.STRING_KEY);
        keyNode.setQuotedString();
        objNode.addChildToBack(IR.propdef(keyNode, valueNode));
      }
      callNode.getParent().replaceChild(callNode, objNode);
      compiler.reportCodeChange();
    }
  }

  /**
   * Returns whether the given call to goog.object.create can be converted to an
   * object literal.
   */
  private static boolean canOptimizeObjectCreateSet(Node firstParam) {
    Node curParam = firstParam;
    while (curParam != null) {
      // All keys must be strings or numbers.
      if (!curParam.isString() && !curParam.isNumber()) {
        return false;
      }
      curParam = curParam.getNext();
    }
    return true;
  }
}