src/java.base/share/classes/java/lang/classfile/instruction/LocalVariable.java

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package java.lang.classfile.instruction;

import java.lang.classfile.ClassFile;
import java.lang.classfile.CodeBuilder;
import java.lang.classfile.CodeElement;
import java.lang.classfile.CodeModel;
import java.lang.classfile.Label;
import java.lang.classfile.PseudoInstruction;
import java.lang.classfile.attribute.LocalVariableInfo;
import java.lang.classfile.attribute.LocalVariableTableAttribute;
import java.lang.classfile.constantpool.Utf8Entry;
import java.lang.constant.ClassDesc;

import jdk.internal.classfile.impl.AbstractPseudoInstruction;
import jdk.internal.classfile.impl.BoundLocalVariable;
import jdk.internal.classfile.impl.TemporaryConstantPool;
import jdk.internal.classfile.impl.Util;

/**
 * A pseudo-instruction which models a single entry in the {@link
 * LocalVariableTableAttribute LocalVariableTable} attribute.  Delivered as a
 * {@link CodeElement} during traversal of the elements of a {@link CodeModel},
 * according to the setting of the {@link ClassFile.DebugElementsOption} option.
 * <p>
 * A local variable entry is composite:
 * {@snippet lang=text :
 * // @link substring="LocalVariable" target="#of(int, String, ClassDesc, Label, Label)" :
 * LocalVariable(
 *     int slot, // @link substring="slot" target="#slot"
 *     String name, // @link substring="name" target="#name"
 *     ClassDesc type, // @link substring="type" target="#type"
 *     Label startScope, // @link substring="startScope" target="#startScope"
 *     Label endScope // @link substring="endScope" target="#endScope"
 * )
 * }
 * Where {@code slot} is within {@code [0, 65535]}.
 * <p>
 * Another model, {@link LocalVariableInfo}, also models a local variable
 * entry; it has no dependency on a {@code CodeModel} and represents of bci
 * values as {@code int}s instead of {@code Label}s, and is used as components
 * of a {@link LocalVariableTableAttribute}.
 *
 * @apiNote
 * {@code LocalVariable} is used for all local variables in Java source code.
 * If a local variable has a parameterized type, a type argument, or an array
 * type of one of the previous types, a {@link LocalVariableType} should be
 * created for that local variable as well.
 *
 * @see LocalVariableInfo
 * @see CodeBuilder#localVariable CodeBuilder::localVariable
 * @see ClassFile.DebugElementsOption
 * @since 24
 */
public sealed interface LocalVariable extends PseudoInstruction
        permits AbstractPseudoInstruction.UnboundLocalVariable, BoundLocalVariable {
    /**
     * {@return the local variable slot}
     * The value is within {@code [0, 65535]}.
     */
    int slot();

    /**
     * {@return the local variable name}
     */
    Utf8Entry name();

    /**
     * {@return the local variable field descriptor string}
     *
     * @apiNote
     * A symbolic descriptor for the type of the local variable is available
     * through {@link #typeSymbol() typeSymbol()}.
     */
    Utf8Entry type();

    /**
     * {@return the local variable type, as a symbolic descriptor}
     */
    default ClassDesc typeSymbol() {
        return Util.fieldTypeSymbol(type());
    }

    /**
     * {@return the start range of the local variable scope}
     */
    Label startScope();

    /**
     * {@return the end range of the local variable scope}
     */
    Label endScope();

    /**
     * {@return a local variable pseudo-instruction}
     * {@code slot} must be within {@code [0, 65535]}.
     *
     * @param slot the local variable slot
     * @param nameEntry the local variable name
     * @param descriptorEntry the local variable descriptor
     * @param startScope the start range of the local variable scope
     * @param endScope the end range of the local variable scope
     * @throws IllegalArgumentException if {@code slot} is out of range
     */
    static LocalVariable of(int slot, Utf8Entry nameEntry, Utf8Entry descriptorEntry, Label startScope, Label endScope) {
        return new AbstractPseudoInstruction.UnboundLocalVariable(slot, nameEntry, descriptorEntry,
                                                                  startScope, endScope);
    }

    /**
     * {@return a local variable pseudo-instruction}
     * {@code slot} must be within {@code [0, 65535]}.
     *
     * @param slot the local variable slot
     * @param name the local variable name
     * @param descriptor the local variable descriptor
     * @param startScope the start range of the local variable scope
     * @param endScope the end range of the local variable scope
     * @throws IllegalArgumentException if {@code slot} is out of range
     */
    static LocalVariable of(int slot, String name, ClassDesc descriptor, Label startScope, Label endScope) {
        return of(slot,
                  TemporaryConstantPool.INSTANCE.utf8Entry(name),
                  TemporaryConstantPool.INSTANCE.utf8Entry(descriptor),
                  startScope, endScope);
    }
}