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MixedReturnTypeCoercion

Emitted when Psalm cannot be sure that part of an array/iterable return type's constraints can be fulfilled

<?php

/**
 * @return string[]
 */
function foo(array $a) : array {
    return $a;
}

This can happen with variadic arguments when @no-named-arguments is not specified:

<?php

/** @return list<int> */
function foo(int ...$args): array {
    return $args; // $args is array<array-key, int> since it can have named arguments
}