com.google.javascript.jscomp.RewriteGlobalDeclarationsForTryCatchWrapping 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.

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/*
 * Copyright 2008 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.ArrayListMultimap;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimaps;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.ArrayList;
import java.util.List;
import java.util.Map.Entry;

/**
 * Moves top-level function declarations to the top of the enclosing JSChunk and rewrites class
 * declarations.
 *
 * Enable this pass if a try catch block wraps the output after compilation, and the output runs
 * on Firefox because function declarations are only defined when reached inside a try catch block
 * on older versions of Firefox.
 *
 * 
On Firefox versions <= 45 (March 2016), this code works:
 *
 * 
var g = f; function f() {}
 *
 * 
but this code does not work:
 *
 * 
try { var g = f; function f() {} } catch(e) {}
 *
 * 
NOTE: As of Firefox version 46 the above code works. Projects not supporting older versions of
 * Firefox shouldn't need this pass.
 *
 * 
RescopeGlobalSymbols still depends on this pass running first to preserve function hoisting
 * semantics.
 *
 * 
NOTE: This pass is safe to turn on by default and delete the associated compiler option.
 * However, we don't do that because the pass is only useful for code wrapped in a try/catch, and
 * otherwise it makes debugging harder because it moves code around.
 *
 * NOTE: now that this pass also moves class declarations it should be renamed along with the
 * associated options.
 */
class RewriteGlobalDeclarationsForTryCatchWrapping implements NodeTraversal.Callback, CompilerPass {
  private final AbstractCompiler compiler;
  private final ListMultimap functions = ArrayListMultimap.create();
  private final ArrayList classes = new ArrayList<>();

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

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, root, this);
    for (Entry> entry : Multimaps.asMap(functions).entrySet()) {
      Node addingRoot = compiler.getNodeForCodeInsertion(entry.getKey());
      List fnNodes = Lists.reverse(entry.getValue());
      if (!fnNodes.isEmpty()) {
        for (Node n : fnNodes) {
          Node parent = n.getParent();
          n.detach();
          compiler.reportChangeToEnclosingScope(parent);

          Node nameNode = n.getFirstChild();
          String name = nameNode.getString();
          nameNode.setString("");
          addingRoot.addChildToFront(IR.var(IR.name(name), n).srcrefTreeIfMissing(n));
          compiler.reportChangeToEnclosingScope(nameNode);
        }
        compiler.reportChangeToEnclosingScope(addingRoot);
      }
    }

    for (Node n : classes) {
      // rewrite CLASS > NAME ... => VAR > NAME > CLASS > EMPTY ...
      Node originalNameNode = n.getFirstChild();
      originalNameNode.replaceWith(IR.empty());
      Node var = IR.var(originalNameNode);
      n.replaceWith(var);
      originalNameNode.addChildToFront(n);
      compiler.reportChangeToEnclosingScope(n);
    }
  }

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    Node grandparent = n.getAncestor(2);
    return grandparent == null || !grandparent.isScript();
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (parent == null || !parent.isScript()) {
      return;
    }

    if (NodeUtil.isFunctionDeclaration(n)) {
      functions.put(t.getChunk(), n);
    }

    if (NodeUtil.isClassDeclaration(n)) {
      classes.add(n);
    }

    if (n.isConst() || n.isLet()) {
      n.setToken(Token.VAR);
      compiler.reportChangeToEnclosingScope(n);
    }
  }
}