[Development] What's our policy on changing the result of qHash(T, 0) between major releases?

[Thiago Macieira]

On Monday, 5 February 2024 01:36:39 PST Marc Mutz via Development wrote:
> I've always understood it such that we as Qt must preserve the property
> that the hash for equal elements is equal within _one_ run of _one_
> process. This means you can use the hash in I/O in any way. That's why
> we have qt_hash, which you _can_ (and do) use in I/O (but is private
> API, AFAIK). I never thought that a hash seed of zero would change that,
> but of course users may have come to depend on this (Hyrum's Law), so a
> [ChangeLog] would be in order.

In commit e3f05981cbeb0b7721f960ef88effa77be2af5ce, I added this comment to 
qHashBits:
    // mix in the length as a secondary seed. For seed == 0, seed2 must be
    // size, to match what we used to do prior to Qt 6.2.

Which is why I am asking now, because making this change would go against that 
comment. But there was no discussion in the change about whether this was 
correct or not. It seems I just write it like that.

However, that was qHashBits(). The change I'm talking about is 
qHash(QLatin1StringView), specifically so it won't call qHashBits().
-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Cloud Software Architect - Intel DCAI Cloud Engineering
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