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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 2014 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.collect.ImmutableSet;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import java.util.LinkedHashSet;
import java.util.Set;

/**
 * A compiler pass to normalize externs by declaring global names on
 * the "window" object, if it is declared in externs.
 * The new declarations are added to the window instance, not to Window.prototype.
 */
class DeclaredGlobalExternsOnWindow implements CompilerPass, NodeTraversal.Callback {

  private static final String WINDOW_NAME = "window";

  private final AbstractCompiler compiler;
  private final Set nodes = new LinkedHashSet<>();

  // Whether there is a "var window" declaration in the externs.
  private boolean windowInExterns = false;

  public DeclaredGlobalExternsOnWindow(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, externs, this);
    addWindowProperties();
  }

  private void addWindowProperties() {
    if (!nodes.isEmpty()) {
      for (Node node : nodes) {
        addExtern(node, windowInExterns);
        compiler.reportChangeToEnclosingScope(node);
      }
    }
  }

  private static void addExtern(Node node, boolean defineOnWindow) {
    String name = node.getString();
    JSDocInfo oldJSDocInfo = NodeUtil.getBestJSDocInfo(node);

    Node globalRef = defineOnWindow ? IR.name(WINDOW_NAME) : IR.thisNode();
    Node getprop = IR.getprop(globalRef, name);
    Node newNode = getprop;

    if (oldJSDocInfo != null) {
      JSDocInfo.Builder builder;

      if (oldJSDocInfo.isConstructorOrInterface()
          || oldJSDocInfo.hasEnumParameterType()) {
        Node nameNode = IR.name(name);
        newNode = IR.assign(getprop, nameNode);

        builder = JSDocInfo.builder();
        if (oldJSDocInfo.isConstructor()) {
          builder.recordConstructor();
        }
        if (oldJSDocInfo.isInterface()) {
          builder.recordInterface();
        }
        if (oldJSDocInfo.usesImplicitMatch()) {
          builder.recordImplicitMatch();
        }
        if (oldJSDocInfo.hasEnumParameterType()) {
          builder.recordEnumParameterType(oldJSDocInfo.getEnumParameterType());
        }
      } else {
        if (NodeUtil.isNamespaceDecl(node)) {
          newNode = IR.assign(getprop, IR.name(name));
        } else {
          Node rhs = NodeUtil.getRValueOfLValue(node);
          // Type-aliasing definition
          if (oldJSDocInfo.hasConstAnnotation() && rhs != null && rhs.isQualifiedName()) {
            newNode = IR.assign(getprop, rhs.cloneTree());
          }
        }
        builder = JSDocInfo.Builder.copyFrom(oldJSDocInfo);
      }

      // TODO(blickly): Remove these suppressions when all externs declarations on window are gone.
      builder.recordSuppressions(ImmutableSet.of("const", "duplicate"));
      JSDocInfo jsDocInfo = builder.build();
      newNode.setJSDocInfo(jsDocInfo);
    }

    newNode.srcrefTree(node);
    newNode.setOriginalName(name);
    newNode.makeNonIndexableRecursive();
    node.getGrandparent().addChildToBack(IR.exprResult(newNode));
  }

  @Override
  public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
    return parent == null
        || NodeUtil.isControlStructure(parent)
        || NodeUtil.isStatementBlock(parent);
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (n.isFunction()) {
      nodes.add(n.getFirstChild());
    } else if (n.isVar()) {
      for (Node c = n.getFirstChild(); c != null; c = c.getNext()) {
        if (c.getString().equals(WINDOW_NAME)) {
          windowInExterns = true;
          continue;
        }
        // Skip 'location' since there is an existing definition
        // for window.location which conflicts with the "var location" one.
        if (!c.getString().equals("location")) {
          nodes.add(c);
        }
      }
    }
  }

}