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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 2016 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.ImmutableMap;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.FunctionType;
import com.google.javascript.rhino.jstype.JSType;

/**
 * Performs correctness checks which are specific to J2CL-generated patterns.
 */
public class J2clChecksPass extends AbstractPostOrderCallback implements CompilerPass {

  static final DiagnosticType J2CL_REFERENCE_EQUALITY =
      DiagnosticType.warning(
          "JSC_J2CL_REFERENCE_EQUALITY",
          "Reference equality may not be used with the specified type: {0}");

  /** Types for which using reference equality is an error. Mapped from name to filename. */
  static final ImmutableMap REFERENCE_EQUALITY_TYPE_PATTERNS =
      ImmutableMap.of(
          "java.lang.Integer", "java/lang/Integer.impl.java.js",
          "java.lang.Float", "java/lang/Float.impl.java.js",
          "goog.math.Long", "javascript/closure/math/long.js");

  private final AbstractCompiler compiler;

  J2clChecksPass(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void visit(NodeTraversal unused, Node n, Node parent) {
    for (String typeName : REFERENCE_EQUALITY_TYPE_PATTERNS.keySet()) {
      checkReferenceEquality(n, typeName, REFERENCE_EQUALITY_TYPE_PATTERNS.get(typeName));
    }
  }

  /** Reports an error if the node is a reference equality check of the specified type. */
  private void checkReferenceEquality(Node n, String typeName, String fileName) {
    if (n.isSHEQ() || n.isEQ() || n.isSHNE() || n.isNE()) {
      JSType firstJsType = n.getFirstChild().getJSType();
      JSType lastJsType = n.getLastChild().getJSType();
      boolean hasType = isType(firstJsType, fileName) || isType(lastJsType, fileName);
      boolean hasNullType = isNullType(firstJsType) || isNullType(lastJsType);
      if (hasType && !hasNullType) {
        compiler.report(JSError.make(n, J2CL_REFERENCE_EQUALITY, typeName));
      }
    }
  }

  private boolean isNullType(JSType jsType) {
    if (jsType == null) {
      return false;
    }
    return jsType.isNullType() || jsType.isVoidType();
  }

  private boolean isType(JSType jsType, String fileName) {
    if (jsType == null) {
      return false;
    }
    jsType = jsType.restrictByNotNullOrUndefined();
    if (jsType.toMaybeObjectType() == null) {
      return false;
    }
    String sourceName = getSourceName(jsType);
    return sourceName != null && sourceName.endsWith(fileName);
  }

  private String getSourceName(JSType jsType) {
    FunctionType constructor = jsType.toMaybeObjectType().getConstructor();
    if (constructor == null) {
      return "";
    }
    return NodeUtil.getSourceName(constructor.getSource());
  }

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