array_unique: explain what the 7.2 rebuild actually changes - #5825
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The 7.2.0 entry mentioned array packing, an engine detail, and left 'different numeric indexes' unexplained. The keys of the returned elements are unchanged; what differs is the index generated when an element is appended afterwards, and only when the element carrying the largest integer key was among the removed duplicates. The 7.2 migration guide carried the same sentence and is updated too.
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The 7.2.0 changelog entry mentioned array packing, an engine detail, and left "different numeric indexes" unexplained. The 7.2 migration guide carried the same sentence, so both are updated.
The keys of the returned elements are the same before and after 7.2: the old implementation copied the array and removed the non-unique elements, the current one adds them to a new array with
zend_hash_index_add_new, keeping the original key either way.What differs is the index generated when an element is appended to the result afterwards, and only when the element carrying the largest integer key was among the removed duplicates. The counter behind
$a[] =is never lowered by a deletion, so the old copy kept the value inherited from the input.Fixes: #4370