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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.transpile;

import java.net.URI;

/**
 * Common interface for a transpiler.
 *
 * 
 * There are a number of considerations when implementing this interface.
 * Specifically,
 * 

 * Which compiler and options to use, including language mode and any
 * specific Compiler subclass. This is handled by {@code BaseTranspiler}
 * accepting a {@code CompilerSupplier}.
 * 
Whether or not to generate external or embedded source maps. This
 * is handled by returning a {@link TranspileResult}, which is able to
 * return any combination of embedded or external source map.
 * 
Specification of a {@code sourceURL}, handling of {@code goog.module},
 * or other postprocessing, such as wrapping the script in {@code eval}.
 * This is left to other collaborators.
 * 
Caching. This is handled by a {@code CachingTranspiler} that
 * decorates an existing {@code Transpiler} with caching behavior.
 * 
 */
public interface Transpiler {
  /** Transforms the given chunk of code. The input should be an entire file worth of code. */
  TranspileResult transpile(URI path, String code);

  /**
   * Returns any necessary runtime code as a string.  This should include
   * everything that could possibly be required at runtime, regardless of
   * whether it's actually used by any of the code that will be transpiled.
   */
  String runtime();

  /** Null implementation that does no transpilation at all. */
  Transpiler NULL =
      new Transpiler() {
        @Override
        public TranspileResult transpile(URI path, String code) {
          return new TranspileResult(path, code, code, "");
        }

        @Override
        public String runtime() {
          return "";
        }
      };
}