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MissingInterfaceImmutableAnnotation

Emitted when an interface is not annotated with @psalm-pure, @psalm-immutable, @psalm-external-mutation-free or @psalm-mutable: to fix, mark the interface with one of the two annotations, enforcing immutability (or mutability) for all properties and methods of implementing classes.

This issue is emitted to aid security analysis, which works best when all explicitly immutable interfaces and classes are marked as immutable.

<?php

/** @api */
interface SomethingPotentiallyImmutable {
    public function someInteger() : int;
}

final class A implements SomethingPotentiallyImmutable {
    public function someInteger() : int {
        return 0;
    }
}