NPE when formatting java file with java 21 preview features.

[sureshg]

Env

$ openjdk 21-ea 2023-09-19
OpenJDK Runtime Environment (build 21-ea+20-1677)
OpenJDK 64-Bit Server VM (build 21-ea+20-1677, mixed mode, sharing)

google-javaformat              = "1.17.0"

Error

> Task :spotlessJava FAILED
Step 'google-java-format' found problem in 'src/main/java/xxx/DOP.java':
57:10: error: java.lang.NullPointerException: Cannot invoke "com.sun.tools.javac.tree.JCTree.getStartPosition()" because "node" is null
        at com.google.googlejavaformat.java.JavaInputAstVisitor.sync(JavaInputAstVisitor.java:3933)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.visitToDeclare(JavaInputAstVisitor.java:2799)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.visitEnhancedForLoop(JavaInputAstVisitor.java:791)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.visitEnhancedForLoop(JavaInputAstVisitor.java:167)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCEnhancedForLoop.accept(JCTree.java:1248)
        at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.scan(JavaInputAstVisitor.java:357)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.visitStatements(JavaInputAstVisitor.java:2229)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.methodBody(JavaInputAstVisitor.java:1550)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.visitMethod(JavaInputAstVisitor.java:1537)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.visitMethod(JavaInputAstVisitor.java:167)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:944)
        at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.scan(JavaInputAstVisitor.java:357)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.addBodyDeclarations(JavaInputAstVisitor.java:3760)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.visitClassDeclaration(JavaInputAstVisitor.java:2044)
        at com.google.googlejavaformat.java.java17.Java17InputAstVisitor.visitClass(Java17InputAstVisitor.java:120)
        at com.google.googlejavaformat.java.java17.Java17InputAstVisitor.visitClass(Java17InputAstVisitor.java:51)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:851)
        at jdk.compiler/com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:92)
        at com.google.googlejavaformat.java.JavaInputAstVisitor.scan(JavaInputAstVisitor.java:357)

I am not sure for which part it's failing. I was playing the java 21 preview features. So here is the sample file used in the task

Sample

import org.jspecify.annotations.NullMarked;

import java.io.*;
import java.lang.reflect.RecordComponent;
import java.nio.file.Files;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;

import static java.lang.System.out;
import static java.util.Objects.requireNonNull;

public class DOP {

    public static void main(String[] args) throws Exception {
        run();
    }

    public static void run() throws Exception {
        @NullMarked
        record Person(String name, int age) {
        }

        var future = new CompletableFuture<>();
        var textBlock = """
                This is text block
                This will join \
                with the line : %s
                "quote" = "added"
                Escape Start  \n \t \r \b \f end
                Space Escape-\s\s\s\s\s\s\s\s\s\s-end
                Regex \\S \\d \\D \\w \\W
                \\d+
                Escape char: \u0020 \u00A0 \u2000 \u3000 \uFEFF \u200B \u200C \u200D \u2028 \u2029
                END
                """
                .formatted(new Person("Foo", 40));
        future.complete(textBlock);
        out.println(future.get());

        amberReflections();
        recordPatterns();
        genericRecordPattern();
        serializeRecord();
    }

    private static void recordPatterns() {
        record Point(int x, int y) {
        }
        var points = List.of(new Point(1, 2), new Point(3, 4), new Point(5, 6));
        // Record pattern in enhanced for loop
        for (Point(var x, var y) : points) {
            out.println("Point: (" + x + ", " + y + ")");
        }
    }

    interface Name<T> {
    }

    record FullName<T>(T firstName, T lastName) implements Name<T> {
    }

    private static void print(Name name) {
        var result = switch (name) {
            case FullName(var first, var last) -> first + ", " + last;
            default -> "Invalid name";
        };
        out.println(result);

        if (name instanceof FullName<?> f) {
            // out.println(f.firstName() + ", " + f.lastName());
        }

        // Named record pattern is not supported
        if (name instanceof FullName(var first, var last)) {
            // out.println(first + ", " + last);
        }
    }

    private static void genericRecordPattern() {
        print(new FullName<>("Foo", "Bar"));
        print(new FullName<>(1, 2));
        print(new FullName<>(10L, 20L));
    }

    private static void amberReflections() {
        var sealedClazz = Result.class;
        out.println("Result (Interface)  -> " + sealedClazz.isInterface());
        out.println("Result (Sealed Class) -> " + sealedClazz.isSealed());

        for (Class<?> permittedSubclass : sealedClazz.getPermittedSubclasses()) {
            out.println("\nPermitted Subclass : " + permittedSubclass.getName());
            if (permittedSubclass.isRecord()) {
                out.println(permittedSubclass.getSimpleName() + " record components are,");
                for (RecordComponent rc : permittedSubclass.getRecordComponents()) {
                    out.println(rc);
                }
            }
        }
    }


    private static void serializeRecord() throws Exception {
        // Local record
        record Lang(String name, int year) implements Serializable {

            Lang {
                requireNonNull(name);
                if (year <= 0) {
                    throw new IllegalArgumentException("Invalid year " + year);
                }
            }
        }

        var serialFile = Files.createTempFile("record-serial", "data").toFile();
        serialFile.deleteOnExit();

        try (var oos = new ObjectOutputStream(new FileOutputStream(serialFile))) {
            List<Record> recs = List.of(
                    new Lang("Java", 25),
                    new Lang("Kotlin", 10),
                    (Record) Result.success(100)
            );

            for (Record rec : recs) {
                out.println("Serializing record: " + rec);
                oos.writeObject(rec);
            }
            oos.writeObject(null); // EOF
        }

        try (var ois = new ObjectInputStream(new FileInputStream(serialFile))) {
            Object rec;
            while ((rec = ois.readObject()) != null) {
                var result = switch (rec) {
                    case null -> "n/a";
                    case Lang l when l.year >= 20 -> l.toString();
                    case Lang(var name, var year) -> name;
                    case Result<?> r -> "Result value: " + r.getOrNull();
                    default -> "Invalid serialized data. Expected Result, but found " + rec;
                };

                out.println("Deserialized record: " + rec);
                out.println(result);
            }
        }

        results().forEach(r -> {
            var result = switch (r) {
                case null -> "n/a";
                case Result.Success<?> s -> s.toString();
                case Result.Failure<?> f -> f.toString();
            };
            out.println("Result (Sealed Type): " + result);
        });
    }

    static List<Result<?>> results() {
        return Arrays.asList(getResult(5), getResult(25), getResult(-1));
    }

    static Result<Number> getResult(long l) {
        // Unnecessary boxing required for boolean check in switch expression
        return switch (Long.valueOf(l)) {
            case Long s when s > 0 && s < 10 -> Result.success(s);
            case Long s when s > 10 -> Result.failure(new IllegalArgumentException(String.valueOf(s)));
            default -> null;
        };
    }
}

[sormuras]

``@sureshg mind that JEP 440 removes the support for record patterns in enhanced for-loops.

History
Record patterns were proposed as a preview feature by JEP 405 and delivered in JDK 19, and previewed a second time by JEP 432 and delivered in JDK 20.
[...]
Apart from some minor editorial changes, the main change since the second preview is to remove support for record patterns appearing in the header of an enhanced for statement. This feature may be re-proposed in a future JEP.

My guess is that your JDK 21-ea version already dropped the support and therefore jdk.compiler/com.sun.tools.javac.tree.JCTree$JCEnhancedForLoop.accept(...) stumbles.

Your code uses such a for-loop here:

        // Record pattern in enhanced for loop
        for (Point(var x, var y) : points) {
            out.println("Point: (" + x + ", " + y + ")");
        }

[sureshg]

@sormuras thanks, i missed that part. I am using the latest ea build 21-ea+20 . The thing is, it still compiles and run from command line. The issue is only when running the formatting task.

...
Point: (1, 2)
Point: (3, 4)
Point: (5, 6)

[sureshg]

Removing record pattern from for loop causes another error

67:32: error: did not generate token "("
com.google.googlejavaformat.java.FormatterException: 67:32: error: did not generate token "("
        at com.google.googlejavaformat.java.Formatter.getFormatReplacements(Formatter.java:275)
        at com.google.googlejavaformat.java.Formatter.formatSource(Formatter.java:247)
        at com.google.googlejavaformat.java.Formatter.formatSource(Formatter.java:213)
        at com.diffplug.spotless.glue.java.GoogleJavaFormatFormatterFunc.apply(GoogleJavaFormatFormatterFunc.java:57)
        at com.diffplug.spotless.FormatterFunc.apply(FormatterFunc.java:32)
        at com.diffplug.spotless.FormatterStepImpl$Standard.format(FormatterStepImpl.java:82)

[cushon]

67:32: error: did not generate token "("

Pattern matching in switch isn't supported yet, I'm working on fixing that part:

 class T {
   {
     var result = switch (name) {
     case FullName(var first, var last) -> first + ", " + last;
     default -> "Invalid name";
    };
  }
}