"Type mismatch" regression since 4.29 with generics and null-analysis

[chrtmn]

After updating to a new ecj version (4.34), I got a new compiler error that did not occur with the old version or with javac. I traced the new behavior back to ecj version 4.29. There was no error with version 4.28. Further tests revealed that it only occurs when the null analysis is activated. If you deactivate it, the error disappears. The issue was found while using Eclipselink. Below, I have extracted the necessary types into an example.

1. ERROR in ErrorClass.java (at line 3)
        @AnnotationWithClassType(ImplementationClass.class)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^
Type mismatch: cannot convert from Class<ImplementationClass> to Class<? extends AbstractClassInAnnotation>

works:

java -jar ecj-4.28.jar -17 -warn:+nullAnnot *.java
java -jar ecj-4.34.jar -17 -warn:-nullAnnot *.java

error:

java -jar ecj-4.29.jar -17 -warn:+nullAnnot *.java
java -jar ecj-4.34.jar -17 -warn:+nullAnnot *.java

Perhaps it is related to #2941?

AbstractClassInAnnotation.java

// real world: https://github.com/eclipse-ee4j/eclipselink/blob/4.0/foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/descriptors/ClassExtractor.java
public abstract class AbstractClassInAnnotation { }

AnnotationWithClassType.java

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

// real world: https://github.com/eclipse-ee4j/eclipselink/blob/4.0/foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/annotations/ClassExtractor.java
@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
public @interface AnnotationWithClassType {
            Class<? extends AbstractClassInAnnotation> value();
}

AnotherType.java

// completely independent type, referenced in ErrorClass
class AnotherType { }

ImplementationClass.java

 // used as type parameter in ErrorClass
public final class ImplementationClass extends AbstractClassInAnnotation { }

ErrorClass.java

// since ECJ 4.29: "Error: Type mismatch: cannot convert from Class<ImplementationClass> to Class<? extends AbstractClassInAnnotation>"
@AnnotationWithClassType(ImplementationClass.class)
abstract class ErrorClass<A extends AnotherType> { // notice: removing "<A extends AnotherType>" makes the error also disappear
}

[jukzi]

cc @stephan-herrmann because null was mentioned