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

Show more of this group Show more artifacts with this name
Show all versions of closure-compiler Show documentation

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.

There is a newer version: v20240317

Show newest version

/*
 * Copyright 2006 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.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;

import java.util.HashSet;
import java.util.Set;

/**
 * Removes try catch finally blocks from a parse tree for easier debugging
 * (these statements impact both debugging in IE and sometimes even in FF).
 *
 * This changes the semantics of the code and should not be used in production!
 *
 */
class RemoveTryCatch implements CompilerPass {
  private final AbstractCompiler compiler;
  private final Set tryNodesContainingReturnStatements;

  RemoveTryCatch(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.tryNodesContainingReturnStatements = new HashSet();
  }

  /**
   * Do all processing on the root node.
   */
  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, root, new RemoveTryCatchCode());
  }

  private class RemoveTryCatchCode extends AbstractPostOrderCallback {
    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      switch (n.getType()) {
        case Token.TRY:
          // Ignore the try statement if it has the @preserveTry annotation
          // (for expected exceptions).
          JSDocInfo info = n.getJSDocInfo();
          if (info != null && info.shouldPreserveTry()) {
            return;
          }

          Node tryBlock = n.getFirstChild();
          Node catchBlock = tryBlock.getNext();  // may be null or empty
          Node finallyBlock = catchBlock != null ? catchBlock.getNext() : null;

          // Ignore the try statement if it has a finally part and the try
          // block contains an early return.
          if (finallyBlock != null &&
              tryNodesContainingReturnStatements.contains(n)) {
            return;
          }

          // Redeclare vars declared in the catch node to be removed.
          if (catchBlock.hasOneChild()) {
            NodeUtil.redeclareVarsInsideBranch(catchBlock);
          }

          // Disconnect the try/catch/finally nodes from the parent
          // and each other.
          n.detachChildren();

          // try node
          Node block;
          if (!NodeUtil.isStatementBlock(parent)) {
            block = IR.block();
            parent.replaceChild(n, block);
            block.addChildToFront(tryBlock);
          } else {
            parent.replaceChild(n, tryBlock);
            block = parent;
          }

          // finally node
          if (finallyBlock != null) {
            block.addChildAfter(finallyBlock, tryBlock);
          }
          compiler.reportCodeChange();
          break;

        case Token.RETURN:
          for (Node anc = parent;
               anc != null && !anc.isFunction();
               anc = anc.getParent()) {
            if (anc.isTry()) {
              tryNodesContainingReturnStatements.add(anc);
              break;
            }
          }
          break;
      }
    }
  }
}