False positive "Flexible Constructor Bodies is only available with source level 25 and above" with Lombok @RequiredArgsConstructor on Java 21 #4521

Description

I am seeing a false-positive Java compiler diagnostic in VS Code when using Lombok @RequiredArgsConstructor in a Java 21 Maven project.

The project compiles and installs successfully with Maven, but VS Code reports:

The Java feature 'Flexible Constructor Bodies' is only available with source level 25 and above

The source code itself does not use Flexible Constructor Bodies or any Java 25 syntax.

Environment

• VS Code Java extension: redhat.java@1.57.2026093008 (pre-release)
• Project source level: Java 21
• Build system: Maven
• Lombok: used through Maven dependency / annotation processing
• mvn install: SUCCESS

Minimal reproducer

import lombok.RequiredArgsConstructor;

@RequiredArgsConstructor
public class Test {

    private final String value;
}

Maven configuration:

<properties>
    <maven.compiler.release>21</maven.compiler.release>
</properties>

Steps to reproduce

1. Create a Maven project targeting Java 21.
2. Add Lombok.
3. Create a class containing a final field.
4. Add Lombok @RequiredArgsConstructor.
5. Open the project in VS Code with redhat.java@1.57.2026093008.
6. Let the Java Language Server finish importing and analysing the project.

Actual behavior

VS Code reports:

The Java feature 'Flexible Constructor Bodies' is only available with source level 25 and above

even though the source code does not contain a constructor using Flexible Constructor Bodies.

The error appears to be related to the constructor generated by Lombok.

Expected behavior

No Java 25 / Flexible Constructor Bodies diagnostic should be reported.

The generated constructor is equivalent to ordinary Java 21-compatible code:

public Test(String value) {
    this.value = value;
}

Maven result

The project builds successfully:

mvn install
BUILD SUCCESS

Therefore the issue appears to be limited to VS Code / JDT Language Server diagnostics rather than the Maven compiler configuration.

Additional information

The same issue occurs in a real Spring project using:

@RequiredArgsConstructor
public class ProdCatalog {

    private final DoubleThrower<RestFunctionsException, RuntimeException> thrower;

    private final NamedParameterJdbcTemplate jdbc;
}

There is no explicit constructor in the class.

The diagnostic is therefore likely triggered during Lombok/JDT AST processing of the generated required-arguments constructor.

I am using the 1.57 pre-release because of a separate issue present in 1.56.0, so reverting to 1.56.0 is not currently a practical workaround.

Please let me know if a Java Language Server log, Lombok version, complete pom.xml, or a minimal reproducer repository would be useful.