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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 2014 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.ImmutableList;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.JSTypeNative;
import com.google.javascript.rhino.jstype.JSTypeRegistry;
import com.google.javascript.rhino.jstype.ObjectType;
import java.util.Locale;

/**
 * Util functions for converting Es6 to Es5
 */
public final class Es6ToEs3Util {

  public static final DiagnosticType CANNOT_CONVERT =
      DiagnosticType.error("JSC_CANNOT_CONVERT", "This code cannot be converted from ES6. {0}");

  // TODO(tbreisacher): Remove this once we have implemented transpilation for all the features
  // we intend to support.
  public static final DiagnosticType CANNOT_CONVERT_YET =
      DiagnosticType.error(
          "JSC_CANNOT_CONVERT_YET", "ES6 transpilation of ''{0}'' is not yet implemented.");

  static void cannotConvert(AbstractCompiler compiler, Node n, String message) {
    compiler.report(JSError.make(n, CANNOT_CONVERT, message));
  }

  /**
   * Warns the user that the given ES6 feature cannot be converted to ES3
   * because the transpilation is not yet implemented. A call to this method
   * is essentially a "TODO(tbreisacher): Implement {@code feature}" comment.
   */
  static void cannotConvertYet(AbstractCompiler compiler, Node n, String feature) {
    compiler.report(JSError.make(n, CANNOT_CONVERT_YET, feature));
  }

  /**
   * Returns a call to {@code $jscomp.makeIterator} with {@code iterable} as its argument.
   */
  static Node makeIterator(AbstractCompiler compiler, Node iterable) {
    return callEs6RuntimeFunction(compiler, iterable, "makeIterator");
  }

  /**
   * Returns a call to $jscomp.arrayFromIterable with {@code iterable} as its argument.
   */
  static Node arrayFromIterable(AbstractCompiler compiler, Node iterable) {
    JSTypeRegistry registry = compiler.getTypeRegistry();
    JSType arrayType = registry.getNativeType(JSTypeNative.ARRAY_TYPE);

    Node call =
        callEs6RuntimeFunction(compiler, iterable, "arrayFromIterable").setJSType(arrayType);
    call.getFirstChild().setJSType(registry.createFunctionTypeWithVarArgs(arrayType));
    return call;
  }

  static void preloadEs6RuntimeFunction(AbstractCompiler compiler, String function) {
    compiler.ensureLibraryInjected("es6/util/" + function.toLowerCase(Locale.ROOT), false);
  }

  static Node callEs6RuntimeFunction(
      AbstractCompiler compiler, Node iterable, String function) {
    preloadEs6RuntimeFunction(compiler, function);
    return IR.call(
        NodeUtil.newQName(compiler, "$jscomp." + function),
        iterable);
  }

  /** Adds the type t to Node n, and returns n. Does nothing if t is null. */
  static Node withType(Node n, JSType t) {
    if (t != null) {
      n.setJSType(t);
    }
    return n;
  }

  /**
   * Returns the JSType as specified by the typeName.
   * Returns null if shouldCreate is false.
   */
  static JSType createType(boolean shouldCreate, JSTypeRegistry registry, JSTypeNative typeName) {
    if (!shouldCreate) {
      return null;
    }
    return registry.getNativeType(typeName);
  }

  /**
   * Returns the JSType as specified by the typeName and instantiated by the typeArg.
   * Returns null if shouldCreate is false.
   */
  static JSType createGenericType(
      boolean shouldCreate, JSTypeRegistry registry, JSTypeNative typeName, JSType typeArg) {
    if (!shouldCreate) {
      return null;
    }
    ObjectType genericType = (ObjectType) (registry.getNativeType(typeName));
    ObjectType uninstantiated = genericType.getRawType();
    return registry.createTemplatizedType(uninstantiated, ImmutableList.of(typeArg));
  }
}