com.google.javascript.jscomp.gwt.linker.MinimalLinker Maven / Gradle / Ivy

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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. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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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 com.google.common.base.Preconditions;
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.ext.linker.SelectionProperty;
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 {

  /**
   * A configuration property indicating whether {@link MinimalLinker} should export via JSInterop.
   */
  private static final String EXPORT_PROPERTY = "linker.minimal.export";

  /**
   * @param context LinkerContext containing properties
   * @return Whether to export, default false
   */
  private static boolean getExportProperty(LinkerContext context) {
    for (SelectionProperty prop : context.getProperties()) {
      if (EXPORT_PROPERTY.equals(prop.getName())) {
        String value = prop.tryGetValue();
        return value == null ? false : Boolean.parseBoolean(value);
      }
    }
    return false;
  }

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

    // If $wnd is set to this, then JSInterop's normal export will run. If export is false, fake
    // out $wnd ith an empty object (plus Error to work around StackTraceCreator using it in a
    // static block).
    output.append("(function(){var $wnd=").append(export ? "this" : "{'Error':{}}").append(";");

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

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

    // Reset $wnd, and call gwtOnLoad if defined. This invokes the onModuleLoad methods of all
    // loaded modules.
    output.append(
        "this['$gwtExport']=$wnd;$wnd=this;typeof gwtOnLoad==='function'&&gwtOnLoad()})();");

    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);
    boolean export = getExportProperty(context);

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

      String output = formatOutput(js[0], export);
      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;
  }
}