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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 2010 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.testing;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.truth.Correspondence;
import com.google.javascript.jscomp.Compiler;
import com.google.javascript.jscomp.CompilerInput;
import com.google.javascript.jscomp.DiagnosticType;
import com.google.javascript.jscomp.JSError;
import com.google.javascript.jscomp.SourceFile;
import com.google.javascript.rhino.Node;

/** Well known {@link Correspondence} instances for use in tests. */
public final class JSCompCorrespondences {

  public static final Correspondence DIAGNOSTIC_EQUALITY =
      Correspondence.transforming(JSError::getType, "has diagnostic type equal to");

  public static final Correspondence DESCRIPTION_EQUALITY =
      Correspondence.transforming((e) -> e.getDescription(), "has description equal to");

  public static final Correspondence INPUT_NAME_EQUALITY =
      Correspondence.transforming(CompilerInput::getName, "has name equal to");

  public static final Correspondence EQUALITY_WHEN_PARSED_AS_EXPRESSION =
      Correspondence.from(
          (actual, expected) -> parseExpr(expected).isEquivalentTo(actual),
          "matches nodes parsed from");

  @SuppressWarnings("unchecked")
  public static  Correspondence referenceEquality() {
    return (Correspondence) REFERENCE_EQUALITY;
  }

  @SuppressWarnings("ReferenceEquality")
  private static final Correspondence REFERENCE_EQUALITY =
      Correspondence.from((a, b) -> a == b, "is same instance as");

  /** A compiler for parsing snippets of code into AST as leniently as possible. */
  private static final Compiler COMPILER_FOR_PARSING = new Compiler();

  /** Parses {@code expr} into an expression AST as leniently as possible. */
  private static Node parseExpr(String expr) {
    Node exprRoot =
        COMPILER_FOR_PARSING
            .parse(SourceFile.fromCode("expr", "(" + expr + ")")) // SCRIPT
            .getFirstFirstChild(); // EXPR_RESULT > expr
    return checkNotNull(exprRoot, "Failed to parse expression");
  }

  // Not instantiable.
  private JSCompCorrespondences() {}
}