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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.collect.Lists.transform;

import com.google.common.base.Function;
import com.google.common.base.Predicates;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.JSTypeExpression;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import com.google.javascript.rhino.TypeIRegistry;
import com.google.javascript.rhino.jstype.JSType;

import java.util.List;

/**
 * Warn about types in JSDoc that are implicitly nullable.
 * @author [email protected] (Ben Lickly)
 */
public final class ImplicitNullabilityCheck extends AbstractPostOrderCallback
    implements CompilerPass {

  public static final DiagnosticType IMPLICITLY_NULLABLE_JSDOC =
    DiagnosticType.warning(
        "JSC_IMPLICITLY_NULLABLE_JSDOC",
        "Name {0} in JSDoc is implicitly nullable.\n"
        + "Please add a '!' to make it non-nullable,"
        + " or a '?' to make it explicitly nullable.");

  private final AbstractCompiler compiler;

  public ImplicitNullabilityCheck(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverseRootsEs6(compiler, this, externs, root);
  }

  /**
   * Crawls the JSDoc of the given node to find any names in JSDoc
   * that are implicitly null.
   */
  @Override
  public void visit(final NodeTraversal t, final Node n, final Node p) {
    final JSDocInfo info = n.getJSDocInfo();
    if (info == null) {
      return;
    }
    final TypeIRegistry registry = compiler.getTypeIRegistry();

    final List thrownTypes =
        transform(
            info.getThrownTypes(),
            new Function() {
              public Node apply(JSTypeExpression expr) {
                return expr.getRoot();
              }
            });

    for (Node typeRoot : info.getTypeNodes()) {
      NodeUtil.visitPreOrder(typeRoot, new NodeUtil.Visitor() {
        public void visit(Node node) {
          if (!node.isString()) {
            return;
          }
          if (thrownTypes.contains(node)) {
            return;
          }
          Node parent = node.getParent();
          if (parent != null) {
            switch (parent.getType()) {
              case Token.BANG:
              case Token.QMARK:
              case Token.THIS:  // The names inside function(this:Foo) and
              case Token.NEW:   // function(new:Bar) are already non-null.
                return;
              case Token.PIPE: { // Inside a union
                Node gp = parent.getParent();
                if (gp != null && gp.getType() == Token.QMARK) {
                  return; // Inside an explicitly nullable union
                }
                for (Node child : parent.children()) {
                  if (child.isString() && child.getString().equals("null")
                      || child.getType() == Token.QMARK) {
                    return; // Inside a union that contains null or nullable type
                  }
                }
                break;
              }
            }
          }
          String typeName = node.getString();
          if (typeName.equals("null") || registry.getType(typeName) == null) {
            return;
          }
          JSType type = (JSType) registry.createTypeFromCommentNode(node, "[internal]", null);
          if (type.isNullable()) {
            reportWarning(t, node, typeName);
          }
        }
      }, Predicates.alwaysTrue());
    }
  }

  /**
   * Reports an implicitly nullable name in JSDoc warning.
   */
  void reportWarning(NodeTraversal t, Node n, String name) {
    compiler.report(t.makeError(n, IMPLICITLY_NULLABLE_JSDOC, name));
  }
}