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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;

import com.google.common.base.CaseFormat;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.javascript.jscomp.PolymerBehaviorExtractor.BehaviorDefinition;
import com.google.javascript.jscomp.PolymerPass.MemberDefinition;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import java.util.LinkedList;
import java.util.List;
import javax.annotation.Nullable;

/**
 * Parsed Polymer class (element) definition. Includes convenient fields for rewriting the
 * class.
 */
final class PolymerClassDefinition {

  /** The target node (LHS) for the Polymer element definition. */
  final Node target;

  /** The object literal passed to the call to the Polymer() function. */
  final Node descriptor;

  /** The constructor function for the element. */
  final MemberDefinition constructor;

  /** The name of the native HTML element which this element extends. */
  final String nativeBaseElement;

  /** Properties declared in the Polymer "properties" block. */
  final List props;

  /** Flattened list of behavior definitions used by this element. */
  final ImmutableList behaviors;

  /** Language features that should be carried over to the extraction destination. */
  final FeatureSet features;

  PolymerClassDefinition(
      Node target,
      Node descriptor,
      JSDocInfo classInfo,
      MemberDefinition constructor,
      String nativeBaseElement,
      List props,
      ImmutableList behaviors,
      FeatureSet features) {
    this.target = target;
    Preconditions.checkState(descriptor.isObjectLit());
    this.descriptor = descriptor;
    this.constructor = constructor;
    this.nativeBaseElement = nativeBaseElement;
    this.props = props;
    this.behaviors = behaviors;
    this.features = features;
  }

  /**
   * Validates the class definition and if valid, destructively extracts the class definition from
   * the AST.
   */
  @Nullable static PolymerClassDefinition extractFromCallNode(
      Node callNode, AbstractCompiler compiler, GlobalNamespace globalNames) {
    Node descriptor = NodeUtil.getArgumentForCallOrNew(callNode, 0);
    if (descriptor == null || !descriptor.isObjectLit()) {
      // report bad class definition
      compiler.report(JSError.make(callNode, PolymerPassErrors.POLYMER_DESCRIPTOR_NOT_VALID));
      return null;
    }

    int paramCount = callNode.getChildCount() - 1;
    if (paramCount != 1) {
      compiler.report(JSError.make(callNode, PolymerPassErrors.POLYMER_UNEXPECTED_PARAMS));
      return null;
    }

    Node elName = NodeUtil.getFirstPropMatchingKey(descriptor, "is");
    if (elName == null) {
      compiler.report(JSError.make(callNode, PolymerPassErrors.POLYMER_MISSING_IS));
      return null;
    }

    String elNameString = CaseFormat.LOWER_HYPHEN.to(CaseFormat.UPPER_CAMEL, elName.getString());
    elNameString += "Element";

    Node target;
    if (NodeUtil.isNameDeclaration(callNode.getGrandparent())) {
      target = IR.name(callNode.getParent().getString());
    } else if (callNode.getParent().isAssign()) {
      target = callNode.getParent().getFirstChild().cloneTree();
    } else {
      target = IR.name(elNameString);
    }

    JSDocInfo classInfo = NodeUtil.getBestJSDocInfo(target);

    JSDocInfo ctorInfo = null;
    Node constructor = NodeUtil.getFirstPropMatchingKey(descriptor, "factoryImpl");
    if (constructor == null) {
      constructor = IR.function(IR.name(""), IR.paramList(), IR.block());
      constructor.useSourceInfoFromForTree(callNode);
    } else {
      ctorInfo = NodeUtil.getBestJSDocInfo(constructor);
    }

    Node baseClass = NodeUtil.getFirstPropMatchingKey(descriptor, "extends");
    String nativeBaseElement = baseClass == null ? null : baseClass.getString();

    Node behaviorArray = NodeUtil.getFirstPropMatchingKey(descriptor, "behaviors");
    PolymerBehaviorExtractor behaviorExtractor =
        new PolymerBehaviorExtractor(compiler, globalNames);
    ImmutableList behaviors = behaviorExtractor.extractBehaviors(behaviorArray);
    List allProperties = new LinkedList<>();
    for (BehaviorDefinition behavior : behaviors) {
      overwriteMembersIfPresent(allProperties, behavior.props);
    }
    overwriteMembersIfPresent(
        allProperties, PolymerPassStaticUtils.extractProperties(descriptor, compiler));

    FeatureSet newFeatures = null;
    if (!behaviors.isEmpty()) {
      newFeatures = behaviors.get(0).features;
      for (int i = 1; i < behaviors.size(); i++) {
        newFeatures = newFeatures.union(behaviors.get(i).features);
      }
    }

    return new PolymerClassDefinition(
        target,
        descriptor,
        classInfo,
        new MemberDefinition(ctorInfo, null, constructor),
        nativeBaseElement,
        allProperties,
        behaviors,
        newFeatures);
  }

  /**
   * Appends a list of new MemberDefinitions to the end of a list and removes any previous
   * MemberDefinition in the list which has the same name as the new member.
   */
  private static void overwriteMembersIfPresent(
      List list, List newMembers) {
    for (MemberDefinition newMember : newMembers) {
      for (MemberDefinition member : list) {
        if (member.name.getString().equals(newMember.name.getString())) {
          list.remove(member);
          break;
        }
      }
      list.add(newMember);
    }
  }
}