SpEL no longer supports lists for varargs invocations

[sbrannen]

The changes made in conjunction with #33013 resulted in a regression for varargs support in SpEL expressions.

Specifically, before #33013 one could supply an inline list as the varargs array when invoking a varargs constructor, method, or function within a SpEL expression. However, after #33013 an inline list (or collection in general) is no longer converted to an array for varargs invocations. Instead, the list is supplied as a single argument of the resulting varargs array.

See #33013 (comment) and subsequent comments for details.

Although it was never intended that one could supply an inline list as the set of varargs, we concede that this is a regression in existing behavior and will therefore restore this support. However, we do not intend to restore support for converting arbitrary single objects to an array for varargs invocations if the single object is already an instance of the varargs array's component type. In other words, we only intend to restore support for converting a single inline list to a varargs array.

[sbrannen]

After further analysis, it would be possible to limit "list to array conversion" to InlineList for FunctionReference but not for ConstructorExecutor and MethodExecutor, since the latter are generic APIs that do not have access to the child SpelNode.

In light of that, I am repurposing this issue to convert any java.util.List to an array for the purpose of varargs invocations in SpEL.

In addition, I will apply this not only to method and constructor invocations but also to MethodHandle-based function invocations.

In other words, we now intend to restore support for converting a single java.util.List to a varargs array for reflection-based method and constructor invocations and introduce that same support for MethodHandle-based function invocations.

[weiw005]

@sbrannen Thanks for all the communication!

Is it possible to update the documentation (https://docs.spring.io) and call out the nuances, and more importantly for us users to understand the expected behavior that we can safely rely on?

[sbrannen]

Hi @weiw005,

Thanks for all the communication!

You're welcome.

Is it possible to update the documentation (docs.spring.io) and call out the nuances, and more importantly for us users to understand the expected behavior that we can safely rely on?

I don't believe we actually document varargs support at all in SpEL.

So, yes, we can document that. I created #33332 to address that in 6.2.