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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.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;
import org.jspecify.nullness.Nullable;

/** Util functions for transpilation passes */
public final class TranspilationUtil {

  private TranspilationUtil() {} // prevent instantiation

  public static final DiagnosticType CANNOT_CONVERT =
      DiagnosticType.error("JSC_CANNOT_CONVERT", "This code cannot be transpiled. {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", "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 feature cannot be transpiled 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));
  }

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

  /** Returns the JSType as specified by the typeName. Returns null if shouldCreate is false. */
  static @Nullable 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 @Nullable 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));
  }
}