src/main/java/com/google/devtools/common/options/EnumConverter.java

// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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.devtools.common.options;

import com.google.common.base.Ascii;
import java.util.Arrays;
import java.util.Locale;
import net.starlark.java.eval.StarlarkValue;

/**
 * A converter superclass for converters that parse enums.
 *
 * <p>Just subclass this class, creating a zero argument constructor that calls {@link
 * #EnumConverter(Class, String)}.
 *
 * <p>This class compares the input string to the string returned by the toString() method of each
 * enum member in a case-insensitive way. Usually, this is the name of the symbol, but beware if you
 * override toString()!
 */
public abstract class EnumConverter<T extends Enum<T>> extends Converter.Contextless<T> {

  private final Class<T> enumType;
  private final String typeName;

  /**
   * Creates a new enum converter. You *must* implement a zero-argument constructor that delegates
   * to this constructor, passing in the appropriate parameters.
   *
   * @param enumType The type of your enumeration; usually a class literal like MyEnum.class
   * @param typeName The intuitive name of your enumeration, for example, the type name for
   *     CompilationMode might be "compilation mode".
   */
  protected EnumConverter(Class<T> enumType, String typeName) {
    this.enumType = enumType;
    this.typeName = typeName;
  }

  /** Implements {@link Converter#convert(String, Object)}. */
  @Override
  public T convert(String input) throws OptionsParsingException {
    for (T value : enumType.getEnumConstants()) {
      if (Ascii.equalsIgnoreCase(value.toString(), input)) {
        return value;
      }
    }
    throw new OptionsParsingException(
        "Not a valid %s: '%s' (should be %s)".formatted(typeName, input, getTypeDescription()));
  }

  /** Implements {@link #getTypeDescription()}. */
  @Override
  public final String getTypeDescription() {
    return Ascii.toLowerCase(
        Converters.joinEnglishList(Arrays.asList(enumType.getEnumConstants())));
  }

  @Override
  public boolean starlarkConvertible() {
    return StarlarkValue.class.isAssignableFrom(enumType);
  }

  @Override
  @SuppressWarnings("unchecked")
  public String reverseForStarlark(Object converted) {
    if (!starlarkConvertible()) {
      throw new UnsupportedOperationException(
          "%s is not Starlark convertible. Implement StarlarkValue to enable this."
              .formatted(enumType));
    }
    return ((Enum<T>) converted).name().toLowerCase(Locale.ROOT);
  }

  public final Class<T> getEnumType() {
    return enumType;
  }
}