/*
 * Copyright 2016 Google Inc. 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.errorprone.annotations;

import static java.lang.annotation.RetentionPolicy.CLASS;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotation for a method that takes a printf-style format string as an argument followed by
 * arguments for that format string.
 *
 * <p>This annotation is used in conjunction with {@link FormatString} to denote a method that takes
 * a printf-style format string and its format arguments. In any method annotated as {@code
 * FormatMethod} without a {@link FormatString} parameter, the first {@code String} parameter is
 * assumed to be the format string. For example, the following two methods are equivalent:
 *
 * <pre>{@code
 * @FormatMethod void log(Locale l, @FormatString String logMessage, Object... args) {}
 * @FormatMethod void log(Locale l, String logMessage, Object... args) {}
 * }</pre>
 *
 * <p>Using {@link FormatMethod} on a method header will ensure the following for the parameters
 * passed to the method:
 *
 * <ol>
 *   <li>A format string is either:
 *       <ul>
 *         <li>A compile time constant value (see {@link CompileTimeConstant} for more info).
 *             <p>The following example is valid:
 *             <pre>{@code
 * public class Foo {
 *   static final String staticFinalLogMessage = "foo";
 *   @FormatMethod void log(@FormatString String format, Object... args) {}
 *   void validLogs() {
 *     log("String literal");
 *     log(staticFinalLogMessage);
 *   }
 * }
 * }</pre>
 *             <p>However the following would be invalid:
 *             <pre>{@code
 * public class Foo{
 *   @FormatMethod void log(@FormatString String format, Object... args) {}
 *   void invalidLog(String notCompileTimeConstant) {
 *     log(notCompileTimeConstant);
 *   }
 * }
 * }</pre>
 *         <li>An effectively final variable that was assigned to a compile time constant value.
 *             This is to permit the following common case:
 *             <pre>{@code
 * String format = "Some long format string: %s";
 * log(format, arg);
 * }</pre>
 *         <li>Another {@link FormatString} annotated parameter. Ex:
 *             <pre>{@code
 * public class Foo {
 *   static final String staticFinalLogMessage = "foo";
 *   @FormatMethod void log(@FormatString String format, Object... args) {}
 *   @FormatMethod void validLog(@FormatString String format, Object... args) {
 *     log(format, args);
 *   }
 * }
 * }</pre>
 *       </ul>
 *   <li>The format string will be valid for the input format arguments. In the case that the actual
 *       format string parameter has a compile time constant value, this will compare the actual
 *       format string value to the types of the passed in format arguments to ensure validity. In
 *       the case that the actual format string parameter is a parameter that was annotated {@link
 *       FormatString} itself, this will ensure that the types of the arguments passed to the callee
 *       match the types of the arguments in the caller.
 * </ol>
 */
@Documented
@Retention(CLASS)
@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
public @interface FormatMethod {}