Thread

1. [[deprecated("don't call this, call that")]]

   Thomas Munro <thomas.munro@gmail.com> — 2026-04-09T03:34:30Z

   Hi,
   
   While working on 1e7fe06c, I wished I could make functions generate
   compiler warnings:
   
   pg_attribute_deprecated("use pg_mblen_{cstr,range,with_len,unbounded} instead")
   extern int     pg_mblen(const char *mbstr);
   
   That'd avoid accidental reintroduction, and also get extension
   maintainers' attention. $SUBJECT is C23/C++14's syntax, but you've
   long been able to do that with in __attribute__ or __declspec for the
   usual suspects so I looked into which compiler versions introduced
   that and came up with the attached.
   
   The idea would be to back-patch the deprecation warnings, and delete
   the functions in, I guess now, v20.  Then the deprecation notice
   facility would always be there for next time we need it.
   

2. Re: [[deprecated("don't call this, call that")]]

   Michael Paquier <michael@paquier.xyz> — 2026-04-09T03:42:36Z

   On Thu, Apr 09, 2026 at 03:34:30PM +1200, Thomas Munro wrote:
   > The idea would be to back-patch the deprecation warnings, and delete
   > the functions in, I guess now, v20.  Then the deprecation notice
   > facility would always be there for next time we need it.
   
   That would be a nice addition, especially with the recent mblen()
   business (could have used that a few times myself).  So +1 for the
   addition of the macro in the back branches.
   
   Do we need to be that conservative with the removal in v19?  We could
   just pull the deletion switch without waiting for v20, IMO..  With the
   deprecated macro in place, at least folks would be aware of the
   problem.
   --
   Michael
   

3. Re: [[deprecated("don't call this, call that")]]

   Peter Eisentraut <peter@eisentraut.org> — 2026-04-09T10:42:52Z

   On 09.04.26 05:34, Thomas Munro wrote:
   > While working on 1e7fe06c, I wished I could make functions generate
   > compiler warnings:
   > 
   > pg_attribute_deprecated("use pg_mblen_{cstr,range,with_len,unbounded} instead")
   > extern int     pg_mblen(const char *mbstr);
   > 
   > That'd avoid accidental reintroduction, and also get extension
   > maintainers' attention. $SUBJECT is C23/C++14's syntax, but you've
   > long been able to do that with in __attribute__ or __declspec for the
   > usual suspects so I looked into which compiler versions introduced
   > that and came up with the attached.
   
   Yes, this makes sense.  There have been discussions about a deprecated 
   attribute before (such as [0]), but in those cases it was mostly about 
   nagging people about coding style, which had potentially annoying 
   effects for extension authors that want to cover many major versions. 
   But in this case, we are actively encouraging people to get rid of a 
   function use, so it seems like a very suitable use case.
   
   [0]: 
   https://www.postgresql.org/message-id/d80b6adf-4bfd-4172-a9cd-2ad6e23b1a08%40eisentraut.org
   
   > The idea would be to back-patch the deprecation warnings, and delete
   > the functions in, I guess now, v20.  Then the deprecation notice
   > facility would always be there for next time we need it.
   
   It might be enough to put the deprecation attribute into PG19.  That 
   way, extension authors will see it (unless the extension is not 
   supporting PG19, in which case it seems likely that they also won't 
   bother to make any adjustments to avoid deprecated functions).
   
   This piece
   
   +#elif defined(__clang__) || (defined(__GNUC__) && __GNUC__ >= 5)
   +#define pg_attribute_deprecated(message) 
   __attribute__((deprecated(message)))
   
   could be written as
   
   #elif __has_attribute(deprecated)
   ...
   
   __has_attribute works back to PG14.
   
   If you do want to backpatch it, I would skip the C23/C++ branch for 
   versions PG18 and older.  That way, each branch has an internally 
   consistent handling of attributes.  (We have some C23/C++ attributes in 
   PG19, but not before.)
   
   
   
   
   

4. Re: [[deprecated("don't call this, call that")]]

   Bertrand Drouvot <bertranddrouvot.pg@gmail.com> — 2026-04-09T11:31:20Z

   Hi,
   
   On Thu, Apr 09, 2026 at 12:42:36PM +0900, Michael Paquier wrote:
   > On Thu, Apr 09, 2026 at 03:34:30PM +1200, Thomas Munro wrote:
   > > The idea would be to back-patch the deprecation warnings, and delete
   > > the functions in, I guess now, v20.  Then the deprecation notice
   > > facility would always be there for next time we need it.
   > 
   > That would be a nice addition, especially with the recent mblen()
   > business (could have used that a few times myself).  So +1 for the
   > addition of the macro in the back branches.
   > 
   > Do we need to be that conservative with the removal in v19?  We could
   > just pull the deletion switch without waiting for v20, IMO..  With the
   > deprecated macro in place, at least folks would be aware of the
   > problem.
   
   +1 on the idea. FWIW it has also been proposed in [1]. Also good candidates are
   XLogRecPtrIsInvalid() and StaticAssertStmt(). Note that a recent commit made
   use of StaticAssertStmt(), see [2].
   
   [1]: https://postgr.es/m/aRGa87Ab0f3ItWRV@ip-10-97-1-34.eu-west-3.compute.internal
   [2]: https://postgr.es/m/adeNWH5pDawDvvR2%40ip-10-97-1-34.eu-west-3.compute.internal
   
   Regards,
   
   -- 
   Bertrand Drouvot
   PostgreSQL Contributors Team
   RDS Open Source Databases
   Amazon Web Services: https://aws.amazon.com