@behappyleee do you have a particular use case needing this change? Can you share a code snippet of what you are trying to achieve?

I am asking because this code is being shaded in spring and only apply strictly necessary patches there.

@behappyleee do you have a particular use case needing this change? Can you share a code snippet of what you are trying to achieve?

I am asking because this code is being shaded in spring and only apply strictly necessary patches there.

@bclozel
Hi, thanks for checking this!

The reason I applied this change is that I wanted to use Transformer as a functional interface in a small utility module, mainly for passing lambda expressions.
Without the @FunctionalInterface annotation, the interface works, but the annotation helps enforce its intended usage and prevents accidental method additions during local development.

Nothing beyond this is required on Spring’s side, and there’s no need for any additional patches in the shaded code.
My change was only for my own usage outside of Spring’s internal shading logic.

If this causes any concern, feel free to point it out — I can adjust my approach accordingly.

Here’s a small snippet showing how I intended to use the Transformer interface as a functional interface:

Transformer trimTransformer = value -> {
    if (value instanceof String s) {
        return s.trim();
    }
    return value;
};

Object result = trimTransformer.transform("hello  ");

Thanks again for the clarification!