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MissingImmutableAnnotation

Emitted when a potentially immutable interface or class does not have a @psalm-pure, @psalm-immutable or @psalm-external-mutation-free declaration.

To automatically add immutable annotations where needed, run Psalm with --alter --issues=MissingImmutableAnnotation.

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

<?php

/** @api */
final class CouldBeExternallyMutationFree {
    private int $counter = 0;

    /** @psalm-external-mutation-free */
    public function someInteger() : int {
        return ++$this->counter;
    }
}

/** @api */
final class CouldBeImmutable {
}