8308753: Class-File API transition to Preview

Reviewed-by: ihse, mchung, vromero

src/java.base/share/classes/java/lang/classfile/AttributeMapper.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package java.lang.classfile;
+
+import jdk.internal.javac.PreviewFeature;
+
+/**
+ * Bidirectional mapper between the classfile representation of an attribute and
+ * how that attribute is modeled in the API.  The attribute mapper is used
+ * to parse the classfile representation into a model, and to write the model
+ * representation back to a classfile.  For each standard attribute, there is a
+ * predefined attribute mapper defined in {@link Attributes}. For nonstandard
+ * attributes, clients can define their own {@linkplain AttributeMapper}.
+ * Classes that model nonstandard attributes should extend {@link
+ * CustomAttribute}.
+ * @param <A> the attribute type
+ *
+ * @since 22
+ */
+@PreviewFeature(feature = PreviewFeature.Feature.CLASSFILE_API)
+public interface AttributeMapper<A> {
+
+    /**
+     * Attribute stability indicator
+     *
+     * @since 22
+     */
+    @PreviewFeature(feature = PreviewFeature.Feature.CLASSFILE_API)
+    enum AttributeStability {
+
+        /**
+         * The attribute contains only pure data, such as timestamps, and can always be bulk-copied.
+         */
+        STATELESS,
+
+        /**
+         * The attribute contains only pure data and CP refs, so can be bulk-copied when CP sharing is in effect,
+         * and need to be exploded and rewritten when CP sharing is not in effect.
+         */
+        CP_REFS,
+
+        /**
+         * The attribute may contain labels, so need to be exploded and rewritten when the Code array is perturbed.
+         */
+        LABELS,
+
+        /**
+         * The attribute may contain indexes into structured not managed by the library (type variable lists, etc)
+         * and so we consult the {@link ClassFile.AttributesProcessingOption} option to determine whether to preserve
+         * or drop it during transformation.
+         */
+        UNSTABLE,
+
+        /**
+         * The attribute is completely unknown and so we consult the {@link ClassFile.AttributesProcessingOption} option
+         * to determine whether to preserve or drop it during transformation.
+         */
+        UNKNOWN
+    }
+
+    /**
+     * {@return the name of the attribute}
+     */
+    String name();
+
+    /**
+     * Create an {@link Attribute} instance from a classfile.
+     *
+     * @param enclosing The class, method, field, or code attribute in which
+     *                  this attribute appears
+     * @param cf The {@link ClassReader} describing the classfile to read from
+     * @param pos The offset into the classfile at which the attribute starts
+     * @return the new attribute
+     */
+    A readAttribute(AttributedElement enclosing, ClassReader cf, int pos);
+
+    /**
+     * Write an {@link Attribute} instance to a classfile.
+     *
+     * @param buf The {@link BufWriter} to which the attribute should be written
+     * @param attr The attribute to write
+     */
+    void writeAttribute(BufWriter buf, A attr);
+
+    /**
+     * {@return whether this attribute may appear more than once in a given location}
+     *
+     * @implSpec The default implementation returns {@code false}
+     */
+    default boolean allowMultiple() {
+        return false;
+    }
+
+    /**
+     * {@return attribute stability indicator}
+     */
+    AttributeStability stability();
+}