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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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/*
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Bob Jervis
 *   Google Inc.
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

package com.google.javascript.rhino.testing;

import static com.google.common.collect.Streams.stream;
import static com.google.common.truth.Fact.fact;
import static com.google.common.truth.Fact.simpleFact;
import static com.google.common.truth.Truth.assertAbout;

import com.google.common.collect.Streams;
import com.google.common.truth.Fact;
import com.google.common.truth.FailureMetadata;
import com.google.common.truth.StringSubject;
import com.google.common.truth.Subject;
import com.google.errorprone.annotations.CheckReturnValue;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.ArrayList;
import java.util.Optional;
import java.util.function.Function;
import javax.annotation.Nullable;

/**
 * A Truth Subject for the Node class. Usage:
 *
 *  *   import static com.google.javascript.rhino.testing.NodeSubject.assertNode;
 *   ...
 *   assertNode(node1).isEqualTo(node2);
 *   assertNode(node1).hasType(Token.FUNCTION);
 * 
 */
public final class NodeSubject extends Subject {

  private Function serializer;

  @CheckReturnValue
  public static NodeSubject assertNode(Node node) {
    return assertAbout(nodes()).that(node);
  }

  public static Subject.Factory nodes() {
    return NodeSubject::new;
  }

  private NodeSubject(FailureMetadata failureMetadata, Node node) {
    super(failureMetadata, node);
  }

  /**
   * Specify a function to use when rendering {@code Node}s into assertion failure messages.
   *
   * A common choice of serializer is {@link Compiler::toSource}, to as render JavaScript code.
   */
  public NodeSubject usingSerializer(Function serializer) {
    this.serializer = serializer;
    return this;
  }

  @Override
  public void isEqualTo(Object expected) {
    throw new UnsupportedOperationException("Use an overload with a declared type.");
  }

  /**
   * Compare the node-trees of actual and expected.
   *
   * 
The per-node comparison ignores:
   *
   * 

   *   Types
   *   
JSDoc
   *   
Side-effects
   * 
   */
  // TODO(nickreid): This isn't really equality based. Use a different name.
  public void isEqualTo(Node expected) {
    isEqualToInternal(expected, /* checkJsdoc= */ false);
  }

  /**
   * Compare the node-trees of actual and expected.
   *
   * The per-node comparison ignores:
   *
   * 

   *   Types
   *   
Side-effects
   * 
   */
  // TODO(nickreid): This isn't really equality based. Use a different name.
  public void isEqualIncludingJsDocTo(Node expected) {
    isEqualToInternal(expected, /* checkJsdoc= */ true);
  }

  // TODO(nickreid): This isn't really equality based. Use a different name.
  public void isEqualToInternal(Node expected, boolean checkJsdoc) {
    isNotNull();
    assertNode(expected).isNotNull();

    findFirstMismatch(actual(), expected, checkJsdoc)
        .ifPresent(
            (mismatch) -> {
              ArrayList facts = new ArrayList<>();
              facts.add(fact("Actual", serializeNode(actual())));
              facts.add(fact("Expected", serializeNode(expected)));

              Node misActual = mismatch.actual;
              facts.add(fact("Actual mismatch", serializeNode(misActual)));
              if (checkJsdoc) {
                facts.add(fact("Actual JSDoc", jsdocToStringNullsafe(misActual.getJSDocInfo())));
              }

              Node misExpected = mismatch.expected;
              facts.add(fact("Expected mismatch", serializeNode(misExpected)));
              if (checkJsdoc) {
                facts.add(
                    fact("Expected JSDoc", jsdocToStringNullsafe(misExpected.getJSDocInfo())));
              }

              failWithoutActual(simpleFact("Node tree inequality"), facts.toArray(new Fact[0]));
            });
  }

  public NodeSubject isEquivalentTo(Node other) {
    check("isEquivalentTo(%s)", other).that(actual().isEquivalentTo(other)).isTrue();
    return this;
  }

  public NodeSubject isNotEquivalentTo(Node other) {
    check("isEquivalentTo(%s)", other).that(actual().isEquivalentTo(other)).isFalse();
    return this;
  }

  public TypeSubject hasJSTypeThat() {
    return TypeSubject.assertType(actual().getJSTypeRequired());
  }

  public void hasType(Token type) {
    hasToken(type);
  }

  public NodeSubject hasToken(Token token) {
    check("getToken()").that(actual().getToken()).isEqualTo(token);
    return this;
  }

  public NodeSubject isName(String name) {
    check("isName()").that(actual().isName()).isTrue();
    check("getString()").that(actual().getString()).isEqualTo(name);
    return this;
  }

  public NodeSubject isNumber(int value) {
    return isNumber((double) value);
  }

  public NodeSubject isNumber(double value) {
    check("isNumber()").that(actual().isNumber()).isTrue();
    check("getNumber()").that(actual().getDouble()).isEqualTo(value);
    return this;
  }

  public NodeSubject isAssign() {
    check("isAssign()").that(actual().isAssign()).isTrue();
    return this;
  }

  public NodeSubject isThis() {
    check("isThis()").that(actual().isThis()).isTrue();
    return this;
  }

  public NodeSubject isSuper() {
    check("isSuper()").that(actual().isSuper()).isTrue();
    return this;
  }

  public NodeSubject isArrowFunction() {
    check("isArrowFunction()").that(actual().isArrowFunction()).isTrue();
    return this;
  }

  public NodeSubject isCall() {
    check("isCall()").that(actual().isCall()).isTrue();
    return this;
  }

  public NodeSubject isMemberFunctionDef(String name) {
    check("isMemberFunction()").that(actual().isMemberFunctionDef()).isTrue();
    check("getString()").that(actual().getString()).isEqualTo(name);
    return this;
  }

  public NodeSubject matchesQualifiedName(String qname) {
    check("matchesQualifiedName(%s)", qname).that(actual().matchesQualifiedName(qname)).isTrue();
    return this;
  }

  public NodeSubject hasCharno(int charno) {
    check("getCharno()").that(actual().getCharno()).isEqualTo(charno);
    return this;
  }

  public NodeSubject hasLineno(int lineno) {
    check("getLineno()").that(actual().getLineno()).isEqualTo(lineno);
    return this;
  }

  public NodeSubject hasLength(int length) {
    check("getLength()").that(actual().getLength()).isEqualTo(length);
    return this;
  }

  public NodeSubject hasEqualSourceInfoTo(Node other) {
    return hasLineno(other.getLineno()).hasCharno(other.getCharno()).hasLength(other.getLength());
  }

  public NodeSubject isIndexable(boolean isIndexable) {
    check("isIndexable()").that(actual().isIndexable()).isEqualTo(isIndexable);
    return this;
  }

  public NodeSubject hasOriginalName(String originalName) {
    check("getOriginalName()").that(actual().getOriginalName()).isEqualTo(originalName);
    return this;
  }

  public NodeSubject hasChildren(boolean hasChildren) {
    check("hasChildren()").that(actual().hasChildren()).isEqualTo(hasChildren);
    return this;
  }

  @CheckReturnValue
  public StringSubject hasStringThat() {
    return check("getString()").that(actual().getString());
  }

  @Override
  protected String actualCustomStringRepresentation() {
    return serializeNode(actual());
  }

  /**
   * Compare the given node-trees recursively and return the first pair of nodes that differs doing
   * a pre-order traversal.
   *
   * @param jsDoc Whether to check for differences in JSDoc.
   */
  private static Optional findFirstMismatch(
      Node actual, Node expected, boolean jsDoc) {
    if (!actual.isEquivalentTo(
        expected, /* compareType= */ false, /* recurse= */ false, jsDoc, /* sideEffect= */ false)) {
      return Optional.of(new NodeMismatch(actual, expected));
    }

    // `isEquivalentTo` confirms that the number of children is the same.
    return Streams.zip(
            stream(actual.children()),
            stream(expected.children()),
            (actualChild, expectedChild) -> findFirstMismatch(actualChild, expectedChild, jsDoc))
        .filter(Optional::isPresent)
        .findFirst()
        .orElse(Optional.empty());
  }

  /** A pair of nodes that were expected to match in some way but didn't. */
  private static final class NodeMismatch {
    final Node actual;
    final Node expected;

    NodeMismatch(Node actual, Node expected) {
      this.actual = actual;
      this.expected = expected;
    }
  }

  private String serializeNode(Node node) {
    if (serializer != null) {
      return serializer.apply(node);
    } else {
      return node.toStringTree();
    }
  }

  private static String jsdocToStringNullsafe(@Nullable JSDocInfo jsdoc) {
    return jsdoc == null ? "(null)" : jsdoc.toStringVerbose();
  }
}