On Mon, 11 Dec 2023 15:43:12 -0500 Tom Lane <t...@sss.pgh.pa.us> wrote:
> Jehan-Guillaume de Rorthais <j...@dalibo.com> writes: > > It looks like since 586b98fdf1aae, the result type collation of > > "convert_from" is forced to "C", like the patch does for type "name", > > instead of the "default" collation for type "text". > > Well, convert_from() inherits its result collation from the input, > per the normal rules for collation assignment [1]. > > > Looking at hints in the header comment of function "exprCollation", I poked > > around and found that the result collation wrongly follow the input > > collation in this case. > > It's not "wrong", it's what the SQL standard requires. Mh, OK. This is at least a surprising behavior. Having a non-data related argument impacting the result collation seems counter-intuitive. But I understand this is by standard, no need to discuss it. > > I couldn't find anything explaining this behavior in the changelog. It looks > > like a regression to me, but if this is actually expected, maybe this > > deserve some documentation patch? > > The v12 release notes do say > > Type name now behaves much like a domain over type text that has > default collation āCā. Sure, and I saw it, but reading at this entry, I couldn't guess this could have such implication on text result from a function call. That's why I hunt for the precise commit and was surprise to find this was the actual change. > You'd have similar results from an expression involving such a domain, > I believe. > > I'm less than excited about patching the v12 release notes four > years later. Maybe, if this point had come up in a more timely > fashion, we'd have mentioned it --- but it's hardly possible to > cover every potential implication of such a change in the > release notes. This could have been documented in the collation concept page, as a trap to be aware of. A link from the release note to such a small paragraph would have been enough to warn devs this might have implications when mixed with other collatable types. But I understand we can not document all the traps paving the way to the standard anyway. Thank you for your explanation! Regards,