Re: some Page/PageData const stuff

On 02.01.26 20:17, Andres Freund wrote:
> On 2025-01-20 15:01:08 +0100, Peter Eisentraut wrote:
>> This has been committed.
>
> I don't like the const markings in PageGetItem():
>
>
> /*
> * PageGetItem
> * Retrieves an item on the given page.
> *
> * Note:
> * This does not change the status of any of the resources passed.
> * The semantics may change in the future.
> */
> static inline void *
> PageGetItem(const PageData *page, const ItemIdData *itemId)
> {
> Assert(page);
> Assert(ItemIdHasStorage(itemId));
>
> return (void *) (((const char *) page) + ItemIdGetOffset(itemId));
> }
>
> The const for PageData seems like a lie to me, because we cast it away. And
> indeed, we often then use the returned value to set hint bits etc.

I agree this is incorrect. Since no callers appear to rely on the const
qualification of the argument, the easiest solution would be to just
remove it. See attached patch.

(In the future, this might be a candidate for a qualifier-preserving
polymorphic function like the C23 string functions, but that's for
another day.)