test/langtools/tools/javac/patterns/NestedPatternVariablesBytecode.java

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/*
 * @test
 * @bug 8268748
 * @summary Javac generates error opcodes when using nest pattern variables
 * @library /tools/lib
 * @modules jdk.compiler/com.sun.tools.javac.api
 *          jdk.compiler/com.sun.tools.javac.main
 * @build toolbox.ToolBox toolbox.JavacTask
 * @run main NestedPatternVariablesBytecode
 */

import java.nio.file.Path;
import java.util.Arrays;
import java.util.List;
import java.util.stream.StreamSupport;

import java.lang.classfile.*;
import java.lang.classfile.attribute.CodeAttribute;

import toolbox.JavacTask;
import toolbox.TestRunner;
import toolbox.ToolBox;

public class NestedPatternVariablesBytecode extends TestRunner {
    private static final String JAVA_VERSION = System.getProperty("java.specification.version");
    private static final String TEST_METHOD = "test";

    ToolBox tb;
    ClassModel cf;

    public NestedPatternVariablesBytecode() {
        super(System.err);
        tb = new ToolBox();
    }

    public static void main(String[] args) throws Exception {
        NestedPatternVariablesBytecode t = new NestedPatternVariablesBytecode();
        t.runTests();
    }

    @Test
    public void testNestedPatternVariablesBytecode() throws Exception {
        String code = """
                class NestedPatterVariablesTest {
                    String test(Object o) {
                        if (o instanceof CharSequence cs && cs instanceof String s) {
                            return s;
                        }
                        return null;
                    }
                }""";
        Path curPath = Path.of(".");
        new JavacTask(tb)
                .sources(code)
                .outdir(curPath)
                .run();

        cf = ClassFile.of().parse(curPath.resolve("NestedPatterVariablesTest.class"));
        MethodModel testMethod = cf.methods().stream()
                                  .filter(this::isTestMethod)
                                  .findAny()
                                  .orElseThrow();
        CodeAttribute code_attribute = testMethod.findAttribute(Attributes.code()).orElseThrow();

        List<String> actualCode = getCodeInstructions(code_attribute);
        List<String> expectedCode = Arrays.asList(
                "ALOAD_1", "INSTANCEOF", "IFEQ", "ALOAD_1", "CHECKCAST", "ASTORE_2", "ALOAD_2", "INSTANCEOF",
                "IFEQ", "ALOAD_2", "CHECKCAST", "ASTORE_3", "ALOAD_3", "ARETURN", "ACONST_NULL", "ARETURN");
        tb.checkEqual(expectedCode, actualCode);
    }

    boolean isTestMethod(MethodModel m) {
        return m.methodName().equalsString(TEST_METHOD);
    }

    List<String> getCodeInstructions(CodeAttribute code) {
        return code.elementList().stream()
                .filter(ce -> ce instanceof Instruction)
                .map(ins -> ((Instruction) ins).opcode().name())
                .toList();
    }
}