SoyErrorKind.java

/*
 * Copyright 2015 Google Inc.
 *
 * 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.template.soy.error;

import com.google.common.base.Preconditions;
import java.text.MessageFormat;

/**
 * Represents any syntactic or semantic error made by a Soy template author, which can be collected
 * during compilation and displayed back to the author. (In particular, this class is not intended
 * to convey errors in the Soy implementation itself.) The error can be customized with {@link
 * #format string arguments}.
 *
 * <p>Classes that report SoyErrorKinds should declare them as static final fields, making it easy
 * for readers to inspect the errors that the class could report.
 *
 * @author brndn@google.com (Brendan Linn)
 */
public final class SoyErrorKind {

  private final MessageFormat messageFormat;
  private final int requiredArgs;

  private SoyErrorKind(MessageFormat messageFormat) {
    this.messageFormat = messageFormat;
    this.requiredArgs = messageFormat.getFormatsByArgumentIndex().length;
  }

  public String format(Object... args) {
    Preconditions.checkState(
        args.length == requiredArgs,
        "Error format required %s parameters, %s were supplied.",
        requiredArgs,
        args.length);
    return messageFormat.format(args);
  }

  public static SoyErrorKind of(String format) {
    checkFormat(format);
    return new SoyErrorKind(new MessageFormat(format));
  }

  private static void checkFormat(String format) {
    // Check for unmatched single quotes.  MessageFormat has some stupid legacy behavior to support
    // unmatched single quotes which is interpreted as 'escape the rest of the format string', this
    // is error prone.  If someone really wants to do that they can just add a "'" at the end of the
    // string.
    int index = 0;
    char singleQuote = '\'';
    while ((index = format.indexOf(singleQuote, index)) != -1) {
      int nextIndex = format.indexOf(singleQuote, index + 1);
      if (nextIndex == -1) {
        throw new IllegalArgumentException(
            "Found an unmatched single quote at char: " + index + " in '" + format + "'");
      }
      index = nextIndex + 1;
    }
  }

  @Override
  public String toString() {
    return getClass().getSimpleName() + "{" + messageFormat.toPattern() + "}";
  }
}