Expected behavior for annotation property with duplicate value definition

[David Holmes]

Hi Rafael,

On 5/05/2021 6:53 pm, Rafael Winterhalter wrote:
> Hello,
> 
> I was wondering if the current OpenJDK behavior should yield an exception
> or if it is accidental and if so, if it should be altered to avoid
> surprising behavior. If an annotation:
> 
> @interface Sample {
>    String v();
> }
> 
> is added to a member where the property 'v' is assigned a value twice, the
> last added value is returned by the reflection API and no error is raised.
> I recently observed this for ASM-generated code where a value was added
> twice and it led to a longer bug search, but technically this could of
> course also happen when javac or other language compilers generate code. I
> wonder therefore if this should rather yield an error or if this behavior
> should be documented somewhere in case that the change would be possibly
> too disruptive for existing code.

I think you are describing generated bytecode that violates Java 
language rules for Annotation types. That is perfectly legal. The VM's 
notion of what an Annotation type is and how it must behave is much 
broader than that of the Java language.

Cheers,
David

> I am happy to provide a patch to OpenJDK but wonder what exception should
> be thrown when reading the property.
> 
> Best regards, Rafael
>