Re: Fix incorrect const qualification for tbm_add_tuples() and itemptr_to_uint64()

From: Peter Eisentraut <peter(at)eisentraut(dot)org>
To: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>, Postgres hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Fix incorrect const qualification for tbm_add_tuples() and itemptr_to_uint64()
Date: 2025-10-30 10:31:42
Message-ID: 964a4a44-5689-427f-a66a-9584c54eb1e1@eisentraut.org
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On 29.10.25 04:11, Chao Li wrote:
> I noticed a wrong const qualification:
> ```
> void
> tbm_add_tuples(TIDBitmap *tbm, const ItemPointer tids, int ntids,
>   bool recheck)
> ```
>
> This "const" only protects "tids" itself from updating, which is
> meaningless. I believe the real intention should be protecting the
> content "tids" pointing to from updating.
>
> This behavior can be easily proved by the compiler. If we add a line of
> fake code in the function:
> ```
> tids[0].ip_posid = 0;
> ```
>
> With current "const ItemPointer tids", the compiler won't report any
> problem. If we change to "const ItemPointerData *tids", the compiler
> will raise an error due to the assignment to read-only variable.
>
> I searched over the source tree, and found only one more occurrence in
> itemptr_to_uint64(), so I fixed it as well.

I have committed this, and I also found a few more similarly confused
cases across the tree, which I also fixed.

> Also, as I am touching tbm_add_tuples(), I did a tiny change that moved
> the loop variable "i" into "for". Peter Eisentraut just did the same
> change in formatting.c [1].

I don't know, let's leave unrelated changes for a separate patch.

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