`AnnotatedMember.equals()` does not work reliably

[klaasdellschaft]

Hi,

I noticed some strange behavior of the current AnnotatedMember.equals() implementations. Following test case for AnnotatedConstructor.equals() currently fails:

public void testAnnotatedConstructorEquality() {
    ObjectMapper mapper = new ObjectMapper();
    DeserializationConfig context = mapper.getDeserializationConfig();
    JavaType beanType = mapper.constructType(SomeBean.class);

    AnnotatedClass instance1 = AnnotatedClassResolver.resolve(context, beanType, context);
    AnnotatedClass instance2 = AnnotatedClassResolver.resolve(context, beanType, context);

    // Successful
    assertEquals(instance1, instance2);
    assertEquals(instance1.getDefaultConstructor().getAnnotated(), instance2.getDefaultConstructor().getAnnotated());
    
    // Fails
    assertEquals(instance1.getDefaultConstructor(), instance2.getDefaultConstructor());
}

Based on the first two successful assertEquals(...) statements, I would have expected that the third assertEquals(...) should be also successful. However, it currently fails.

The reason for this behavior is that AnnotatedConstructor.equals() is currently using == for comparing the two constructors:

public boolean equals(Object o) {
    if (o == this) return true;
    return ClassUtil.hasClass(o, getClass())
            && (((AnnotatedConstructor) o)._constructor == _constructor);
}

However, the implementation of the reflection API in java.lang.Class is always copying / cloning the Field, Method and Constructor instances prior to returning them to the caller (e.g. see Class.copyConstructors()). Thus, each call of Class.getConstructors() will always return new instances.

If you agree that the above test case should be successful (i.e. also assertEquals(instance1.getDefaultConstructor(), instance2.getDefaultConstructor()) should be successful), I would prepare a corresponding pull request that slightly modifies the current implementation of the equals() method for all subclasses of AnnotatedMember that are affected by this problem (i.e. at least AnnotatedField, AnnotatedConstructor and AnnotatedMethod).

[cowtowncoder]

@klaasdellschaft I think you are right: I was assuming that instances would be equal.

Now... Jackson itself is probably not using equality check for anything (given there is no known issue) but it does seem like it'd make sense to implement equality checks properly. So I'd be happy to review a PR.
For fields (for example) it'd be simple enough: same name, same class Field is declared in; for methods enough to check name, declaring class, and match of type-erased parameter types.