src/java.base/share/classes/java/lang/classfile/attribute/StackMapFrameInfo.java

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package java.lang.classfile.attribute;

import java.lang.classfile.ClassFile;
import java.lang.classfile.Label;
import java.lang.classfile.Opcode;
import java.lang.classfile.constantpool.ClassEntry;
import java.lang.classfile.instruction.BranchInstruction;
import java.lang.constant.ClassDesc;
import java.util.List;

import jdk.internal.classfile.impl.StackMapDecoder;
import jdk.internal.classfile.impl.TemporaryConstantPool;

/**
 * Models a stack map frame in a {@link StackMapTableAttribute StackMapTable}
 * attribute (JVMS {@jvms 4.7.4}).  A stack map frame must appear at the
 * beginning of each basic block in a method (JVMS {@jvms 4.10.1}).
 *
 * @apiNote
 * In general, a stack map frame should be defined for each target of a
 * {@link BranchInstruction}, or unreachable code right after an unconditional
 * branch instruction like {@link Opcode#GOTO goto}.  The automatic stack map
 * generation cannot handle unreachable code right after an unconditional jump;
 * The {@link ClassFile.DeadCodeOption} allows substituting such code, or
 * advanced users can provide their own stack maps for dead code.
 *
 * @see StackMapTableAttribute#entries()
 * @jvms 4.7.4 The {@code StackMapTable} Attribute
 * @jvms 4.10.1 Verification by Type Checking
 * @since 24
 */
public sealed interface StackMapFrameInfo
            permits StackMapDecoder.StackMapFrameImpl {

    /**
     * {@return the raw {@code u1 frame_type}}
     */
    int frameType();

    /**
     * {@return the frame target label}
     */
    Label target();

    /**
     * {@return the expanded local variable types}
     */
    List<VerificationTypeInfo> locals();

    /**
     * {@return the expanded operand stack types}
     */
    List<VerificationTypeInfo> stack();

    /**
     * {@return a new stack map frame}
     *
     * @param target the location of the frame
     * @param locals the complete list of frame locals
     * @param stack the complete frame stack
     */
    public static StackMapFrameInfo of(Label target,
            List<VerificationTypeInfo> locals,
            List<VerificationTypeInfo> stack) {
        return new StackMapDecoder.StackMapFrameImpl(255, target, locals, stack);
    }

    /**
     * The type of a stack or local variable value.
     *
     * @see #locals()
     * @see #stack()
     * @jvms 4.7.4 The {@code StackMapTable} Attribute
     * @since 24
     */
    sealed interface VerificationTypeInfo {

        /** The {@link #tag() tag} for verification type info {@link SimpleVerificationTypeInfo#TOP TOP}. */
        int ITEM_TOP = 0;

        /** The {@link #tag() tag} for verification type info {@link SimpleVerificationTypeInfo#INTEGER INTEGER}. */
        int ITEM_INTEGER = 1;

        /** The {@link #tag() tag} for verification type info {@link SimpleVerificationTypeInfo#FLOAT FLOAT}. */
        int ITEM_FLOAT = 2;

        /** The {@link #tag() tag} for verification type info {@link SimpleVerificationTypeInfo#DOUBLE DOUBLE}. */
        int ITEM_DOUBLE = 3;

        /** The {@link #tag() tag} for verification type info {@link SimpleVerificationTypeInfo#LONG LONG}. */
        int ITEM_LONG = 4;

        /** The {@link #tag() tag} for verification type info {@link SimpleVerificationTypeInfo#NULL NULL}. */
        int ITEM_NULL = 5;

        /** The {@link #tag() tag} for verification type info {@link SimpleVerificationTypeInfo#UNINITIALIZED_THIS UNINITIALIZED_THIS}. */
        int ITEM_UNINITIALIZED_THIS = 6;

        /** The {@link #tag() tag} for verification type info {@link ObjectVerificationTypeInfo OBJECT}. */
        int ITEM_OBJECT = 7;

        /** The {@link #tag() tag} for verification type info {@link UninitializedVerificationTypeInfo UNINITIALIZED}. */
        int ITEM_UNINITIALIZED = 8;

        /**
         * {@return the tag of the type info}
         *
         * @apiNote
         * {@code ITEM_}-prefixed constants in this class, such as {@link #ITEM_TOP}, describe the
         * possible return values of this method.
         */
        int tag();
    }

    /**
     * A simple stack value.
     *
     * @since 24
     */
    public enum SimpleVerificationTypeInfo implements VerificationTypeInfo {

        /** Verification type top. */
        TOP(ITEM_TOP),

        /** Verification type int. */
        INTEGER(ITEM_INTEGER),

        /** Verification type float. */
        FLOAT(ITEM_FLOAT),

        /** Verification type double. */
        DOUBLE(ITEM_DOUBLE),

        /** Verification type long. */
        LONG(ITEM_LONG),

        /** Verification type null. */
        NULL(ITEM_NULL),

        /** Verification type uninitializedThis. */
        UNINITIALIZED_THIS(ITEM_UNINITIALIZED_THIS);


        private final int tag;

        SimpleVerificationTypeInfo(int tag) {
            this.tag = tag;
        }

        @Override
        public int tag() {
            return tag;
        }
    }

    /**
     * A stack value for an object type. Its {@link #tag() tag} is {@value #ITEM_OBJECT}.
     *
     * @jvms 4.7.4 The {@code StackMapTable} Attribute
     * @since 24
     */
    sealed interface ObjectVerificationTypeInfo extends VerificationTypeInfo
            permits StackMapDecoder.ObjectVerificationTypeInfoImpl {

        /**
         * {@return a new object verification type info}
         * @param className the class of the object
         */
        public static ObjectVerificationTypeInfo of(ClassEntry className) {
            return new StackMapDecoder.ObjectVerificationTypeInfoImpl(className);
        }

        /**
         * {@return a new object verification type info}
         * @param classDesc the class of the object
         * @throws IllegalArgumentException if {@code classDesc} represents a primitive type
         */
        public static ObjectVerificationTypeInfo of(ClassDesc classDesc) {
            return of(TemporaryConstantPool.INSTANCE.classEntry(classDesc));
        }

        /**
         * {@return the class of the object}
         */
        ClassEntry className();

        /**
         * {@return the class of the object, as a symbolic descriptor}
         */
        default ClassDesc classSymbol() {
            return className().asSymbol();
        }
    }

    /**
     * An uninitialized stack value. Its {@link #tag() tag} is {@value #ITEM_UNINITIALIZED}.
     *
     * @jvms 4.7.4 The {@code StackMapTable} Attribute
     * @since 24
     */
    sealed interface UninitializedVerificationTypeInfo extends VerificationTypeInfo
            permits StackMapDecoder.UninitializedVerificationTypeInfoImpl {

        /**
         * {@return the label immediately before the {@link Opcode#NEW new}
         * instruction that creates this uninitialized object}
         */
        Label newTarget();

        /**
         * {@return an uninitialized verification type info}
         * @param newTarget the label immediately before the {@link Opcode#NEW new}
         *                  instruction that creates this uninitialized object
         */
        public static UninitializedVerificationTypeInfo of(Label newTarget) {
            return new StackMapDecoder.UninitializedVerificationTypeInfoImpl(newTarget);
        }
    }
}