Re: some Page/PageData const stuff

Hi,

On 2026-01-03 18:05:19 +0100, Peter Eisentraut wrote:
> 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.

LGTM


> (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.)

Makes sense. I doubt this is the place I would start with that though, the
amount of effort that'd take around all the functions dealing with heap tuples
seems too large...

Greetings,

Andres Freund