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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 2009 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 static com.google.common.base.Preconditions.checkState;

import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;
import java.util.HashSet;
import java.util.Set;

/**
 * Collect known properties on the global windows object to avoid creating global variable names
 * that conflict with these names. This pass runs after property renaming but before variable
 * renaming.
 *
 * This is a best effort pass and does not guarantee that there are no conflicts.
 *
 * This is not required if the global variables are isolated from global scope
 * (isolation_mode=IIFE) or equivalent.
 */
class GatherRawExports extends AbstractPostOrderCallback implements CompilerPass {

  private final AbstractCompiler compiler;

  // TODO(johnlenz): "goog$global" should be part of a coding convention.
  // Note: GatherRawExports runs after property renaming and
  // collapse properties, so the two entries here protect goog.global in the
  // two common cases "collapse properties and renaming on" or both off
  // but not the case where only property renaming is on.
  private static final String[] GLOBAL_THIS_NAMES = {
    "window",
    "globalThis",
    "top",
    "self",
    "goog$global",
    "goog.global",
    "$jscomp.global",
    "$jscomp$global"
  };

  private final Set exportedVariables = new HashSet<>();

  GatherRawExports(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

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

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (NodeUtil.isNormalOrOptChainGet(n) && isGlobalThisObject(t, n.getFirstChild())) {
      if (NodeUtil.isNormalOrOptChainGetProp(n)) {
        exportedVariables.add(n.getString());
      } else if (NodeUtil.isNormalOrOptChainGet(n) && n.getSecondChild().isStringLit()) {
        exportedVariables.add(n.getSecondChild().getString());
      }
    }
  }

  private static boolean isGlobalThisObject(NodeTraversal t, Node n) {
    // We should consider using scopes or types to check for references to the "global this".
    if (n.isThis()) {
      return t.inGlobalHoistScope();
    } else if (n.isQualifiedName()) {
      int items = GLOBAL_THIS_NAMES.length;
      for (int i = 0; i < items; i++) {
        if (n.matchesQualifiedName(GLOBAL_THIS_NAMES[i])) {
          return true;
        }
      }
    }
    return false;
  }

  public Set getExportedVariableNames() {
    return exportedVariables;
  }
}