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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 2017 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.Callback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;

/** A simple pass to ensure that all AST nodes that are expressions have types */
final class TypeInfoCheck implements Callback, CompilerPass {
  private final AbstractCompiler compiler;
  private boolean requiresTypes = false;

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

  public void setCheckSubTree(Node root) {
    requiresTypes = true;
    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public void process(Node externs, Node root) {
    requiresTypes = false;
    NodeTraversal.traverse(compiler, root, this);
  }

  @Override
  public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
    if (n.isScript()) {
      // Each JavaScript file is rooted in a script node, so we'll only
      // have type information inside the script node.
      requiresTypes = true;
    } else if (n.isParamList()) {
      // typeI information is not included for children of PARAM_LIST,
      // so we turn off requireTypes for these nodes.
      requiresTypes = false;
    }
    return true;
  }

  @Override
  public void visit(NodeTraversal nodeTraversal, Node n, Node parent) {
    if (n.isScript()) {
      requiresTypes = false;
    } else if (requiresTypes && shouldHaveTypeInformation(n)) {
      if (n.isString() && (parent.isGetProp() || parent.isGetElem())) {
        return;
      }
      if (n.isParamList()) {
        return;
      }
      if (n.isName() && parent.isFunction()) {
        // function names does not need to have type information.
        return;
      }
      if (n.getJSType() == null) {
        throw new IllegalStateException(
            "No type information associated with "
                + n
                + " Most likely a Node has been created after type checking"
                + " without setting the type.");
      }
    }
  }

  private static boolean shouldHaveTypeInformation(Node node) {
    return node.isFunction() || !IR.mayBeStatement(node);
  }
}