1 /*
  2  * Copyright (c) 2019, 2026, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.  Oracle designates this
  8  * particular file as subject to the "Classpath" exception as provided
  9  * by Oracle in the LICENSE file that accompanied this code.
 10  *
 11  * This code is distributed in the hope that it will be useful, but WITHOUT
 12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 14  * version 2 for more details (a copy is included in the LICENSE file that
 15  * accompanied this code).
 16  *
 17  * You should have received a copy of the GNU General Public License version
 18  * 2 along with this work; if not, write to the Free Software Foundation,
 19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 20  *
 21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 22  * or visit www.oracle.com if you need additional information or have any
 23  * questions.
 24  */
 25 
 26 package jdk.internal.javac;
 27 
 28 import java.lang.annotation.*;
 29 
 30 /**
 31  * Indicates the API declaration in question is associated with a
 32  * <em>preview feature</em>. See JEP 12: "Preview Language and VM
 33  * Features" (https://openjdk.org/jeps/12).
 34  *
 35  * Note this internal annotation is handled specially by the javac compiler.
 36  * To work properly with {@code --release older-release}, it requires special
 37  * handling in {@code make/langtools/src/classes/build/tools/symbolgenerator/CreateSymbols.java}
 38  * and {@code src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java}.
 39  *
 40  * @since 14
 41  */
 42 // Match the meaningful targets of java.lang.Deprecated, omit local
 43 // variables and parameter declarations
 44 @Target({ElementType.METHOD,
 45          ElementType.CONSTRUCTOR,
 46          ElementType.FIELD,
 47          ElementType.PACKAGE,
 48          ElementType.MODULE,
 49          ElementType.TYPE})
 50  // CLASS retention will hopefully be sufficient for the purposes at hand
 51 @Retention(RetentionPolicy.CLASS)
 52 // *Not* @Documented
 53 public @interface PreviewFeature {
 54     /**
 55      * Name of the preview feature the annotated API is associated
 56      * with.
 57      */
 58     public Feature feature();
 59 
 60     public boolean reflective() default false;
 61 
 62     /**
 63      * Enum of preview features in the current release.
 64      * Values should be annotated with the feature's {@code JEP}.
 65      */
 66     public enum Feature {
 67         @JEP(number = 8350458, title = "Strict Field Initialization in the JVM", status = "Preview")
 68         STRICT_FIELDS,
 69         @JEP(number=401, title="Value Classes and Objects", status = "Preview")
 70         VALUE_OBJECTS,
 71 
 72         // The JDK build process involves creating an interim javac which is then
 73         // used to compile the rest of the JDK. The jdk.internal.javac.PreviewFeature
 74         // annotation from the current sources is used when compiling interim javac.
 75         // That's because the javac APIs of the current sources may be annotated with
 76         // this annotation and they may be using the enum constants of the current sources.
 77         // Furthermore, when compiling interim javac, the class files from the bootstrap JDK get
 78         // used and those may also contain the PreviewFeature annotation. However, they may be
 79         // using the enum constants of the bootstrap JDK's PreviewFeature annotation.
 80         // If javac sees an annotation with an unknown enum constant, it produces a warning,
 81         // and that in turn fails the build.
 82         // So, in the current sources, we need to preserve the PreviewFeature enum constants
 83         // for as long as the interim javac build needs it. As a result, we retain PreviewFeature
 84         // enum constants for preview features that are present in the bootstrap JDK.
 85         // Older constants can be removed.
 86         //
 87         // For example, Class-File API became final in JDK 24. As soon as JDK 23 was dropped as
 88         // the bootstrap JDK, the CLASSFILE_API enum constant became eligible for removal.

 89         //---
 90         @JEP(number=525, title="Structured Concurrency", status="Sixth Preview")
 91         STRUCTURED_CONCURRENCY,
 92         @JEP(number = 526, title = "Lazy Constants", status = "Second Preview")
 93         LAZY_CONSTANTS,
 94         @JEP(number=524, title="PEM Encodings of Cryptographic Objects",
 95             status="Second Preview")
 96         PEM_API,
 97         LANGUAGE_MODEL,
 98         /**
 99          * A key for testing.
100          */
101         @JEP(number=2_147_483_647, title="Test Feature")
102         TEST,
103         ;
104     }
105 
106     /**
107      * Annotation identifying the JEP associated with a preview feature.
108      */
109     @Target(ElementType.FIELD)
110     @Retention(RetentionPolicy.CLASS)
111     @interface JEP {
112         /** JEP number */
113         int number() default 0;
114         /** JEP title in plain text */
115         String title();
116         /** JEP status such as "Preview", "Second Preview", etc */
117         String status() default "Preview";
118     }
119 }
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