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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 2015 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.gwt.linker;

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

import com.google.gwt.core.ext.LinkerContext;
import com.google.gwt.core.ext.TreeLogger;
import com.google.gwt.core.ext.UnableToCompleteException;
import com.google.gwt.core.ext.linker.AbstractLinker;
import com.google.gwt.core.ext.linker.ArtifactSet;
import com.google.gwt.core.ext.linker.CompilationResult;
import com.google.gwt.core.ext.linker.LinkerOrder;
import com.google.gwt.core.ext.linker.LinkerOrder.Order;
import com.google.gwt.core.linker.SymbolMapsLinker;

/**
 * Simple single-script linker that doesn't add any dependencies on the browser.
 *
 * This is intended to generate JS for servers, Node, or in a self-contained way inside browsers. It
 * doesn't support permutations, nor does it allow late-loading code.
 */
@LinkerOrder(Order.PRIMARY)
public class MinimalLinker extends AbstractLinker {

  /**
   * Formats the application's JS code for output.
   *
   * @param js Code to format.
   * @return Formatted, linked code.
   */
  private static String formatOutput(String js) {
    StringBuilder output = new StringBuilder();

    // Shadow window so that non-browser environments can pass their own global object here.
    output.append("(function(window){");

    // $wnd is set to this, which should allow JSInterop's normal export to run and
    // pollute the global namespace.
    output.append("var $wnd=this;");

    // Shadow $doc, $moduleName and $moduleBase.
    output.append("var $doc={},$moduleName,$moduleBase;");

    // Append output JS.
    output.append(js);

    // 1. Export $gwtExport, needed for transpile.js
    // 2. Reset $wnd (nb. this occurs after jscompiler's JS has run)
    // 3. Call gwtOnLoad, if defined: this invokes onModuleLoad for all loaded modules.
    output.append("this['$gwtExport']=$wnd;$wnd=this;typeof gwtOnLoad==='function'&&gwtOnLoad()");

    // Overspecify the global object, to capture Node and browser environments.
    String globalObject = "this&&this.self||"
        + "(typeof window!=='undefined'?window:(typeof global!=='undefined'?global:this))";

    // Call the outer function with the global object as this and its first argument, so that we
    // fake window in Node environments, allowing our code to do things like "window.console(...)".
    output.append("}).call(").append(globalObject).append(",").append(globalObject).append(");");

    return output.toString();
  }

  @Override
  public String getDescription() {
    return "Minimal";
  }

  @Override
  public ArtifactSet link(TreeLogger logger, LinkerContext context, ArtifactSet artifacts)
      throws UnableToCompleteException {
    ArtifactSet toReturn = link(logger, context, artifacts, true);
    toReturn = link(logger, context, toReturn, false);
    return toReturn;
  }

  @Override
  public ArtifactSet link(
      TreeLogger logger, LinkerContext context, ArtifactSet artifacts, boolean onePermutation)
      throws UnableToCompleteException {
    ArtifactSet toReturn = new ArtifactSet(artifacts);
    ArtifactSet writableArtifacts = new ArtifactSet(artifacts);

    for (CompilationResult result : toReturn.find(CompilationResult.class)) {
      String[] js = result.getJavaScript();
      checkArgument(js.length == 1, "MinimalLinker doesn't support GWT.runAsync");

      String output = formatOutput(js[0]);
      toReturn.add(emitString(logger, output, context.getModuleName() + ".js"));
    }

    for (SymbolMapsLinker.ScriptFragmentEditsArtifact ea :
        writableArtifacts.find(SymbolMapsLinker.ScriptFragmentEditsArtifact.class)) {
      toReturn.add(ea);
    }
    return toReturn;
  }

  @Override
  public boolean supportsDevModeInJunit(LinkerContext context) {
    return false;
  }
}