com.google.javascript.jscomp.MoveFunctionDeclarations Maven / Gradle / Ivy

/*
 * 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.jscomp.NodeTraversal.Callback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import java.util.List;
import java.util.Map.Entry;

/**
 * Moves top-level function declarations to the top of the enclosing JSModule.
 *
 * 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, this code works:
 *
 * 
var g = f; function f() {}
 *
 * 
but this code does not work:
 *
 * 
try { var g = f; function f() {} } catch(e) {}
 *
 * 
NOTE(lharker): 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(dimvar): 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.
 */
class MoveFunctionDeclarations implements Callback, CompilerPass {
  private final AbstractCompiler compiler;
  private final ListMultimap functions;

  MoveFunctionDeclarations(AbstractCompiler compiler) {
    this.compiler = compiler;
    functions = ArrayListMultimap.create();
  }

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

  @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)) {
      parent.removeChild(n);
      compiler.reportChangeToEnclosingScope(parent);

      functions.put(t.getModule(), n);
    }
  }
}