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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;

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

import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;

/**
 * Replicates the effect of {@literal ClosureBundler} in whitespace-only mode and wraps goog.modules
 * in goog.loadModule calls. See comment block below.
 */
public class WhitespaceWrapGoogModules implements CompilerPass {

  private final AbstractCompiler compiler;

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

  @Override
  public void process(Node externs, Node root) {
    for (Node c = root.getFirstChild(); c != null; c = c.getNext()) {
      checkState(c.isScript());
      visitScript(c);
    }
  }

  private void visitScript(Node scriptRoot) {
    if (!NodeUtil.isGoogModuleFile(scriptRoot)) {
      return;
    }
    Node moduleBody = scriptRoot.getFirstChild();
    moduleBody.setToken(Token.BLOCK);
    NodeUtil.tryMergeBlock(moduleBody, true);
    compiler.reportChangeToEnclosingScope(scriptRoot);

    // As per ClosureBundler:
    /*
     // add the prefix on the first line so the line numbers aren't affected.
     out.append(
         "goog.loadModule(function(exports) {"
         + "'use strict';");
     append(out, Mode.NORMAL, contents);
     out.append(
         "\n" // terminate any trailing single line comment.
         + ";" // terminate any trailing expression.
         + "return exports;});\n");
     appendSourceUrl(out, Mode.NORMAL);
    */

    Node block = IR.block();
    block.addChildToBack(
        IR.exprResult(IR.string("use strict"))); // needs to be explicit, to match ClosureBundler

    Node function = IR.function(IR.name(""), IR.paramList(IR.name("exports")), block);
    compiler.reportChangeToChangeScope(function);
    Node loadMod =
        IR.exprResult(IR.call(IR.getprop(IR.name("goog"), "loadModule"), function))
            .srcrefTree(scriptRoot);

    if (scriptRoot.hasChildren()) {
      block.addChildrenToBack(scriptRoot.removeChildren());
    }
    block.addChildToBack(IR.returnNode(IR.name("exports")).srcrefTree(scriptRoot));

    scriptRoot.addChildToBack(loadMod);
    compiler.reportChangeToChangeScope(scriptRoot);
  }
}