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Re: Make copyObject work in C++

Bryan Green <dbryan.green@gmail.com>

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From: Bryan Green <dbryan.green@gmail.com>
To: pgsql-hackers@lists.postgresql.org
Date: 2026-02-04T15:54:37Z
Lists: pgsql-hackers 
On 1/25/2026 6:42 AM, Jelte Fennema-Nio wrote:
> On Tue Jan 20, 2026 at 5:28 PM CET, Peter Eisentraut wrote:
>> I have split your first patch further.  For a start, I left out the
>> PG_MODULE_MAGIC*-related changes and disabled the module under MSVC.
>> This has been committed.  I plan to let the buildfarm run with it for
>> a day or two and then add in the basic MSVC support.
> 
> To hopefully make your life a bit easier. Here's a rebased version that
> enables the MSVC support again, with an updated commit message.
> 
This causes the build to break on VS 2022.  Versions prior do not have
support for __typeof_unqual__.  This would have led to
HAVE_TYPEOF_UNQUAL being not defined on the buildfarm causing the
fallback to copyObjectImpl() for VS 2019.

When you build on VS 2022 you will get an error:
../src/backend/commands/event_trigger.c(1901): error C2100: you cannot
dereference an operand of type 'void'

VS 2022 (MSVC) does not handle the void * dereference the way gcc/clang
does (thanks to GNU extensions, I believe).  It exposes
__typeof_unqual__ even it C11, but enforces strict C semantics on the
void * dereference.  To work on this platform the call
copyObject(lfirst(cell)) would need to have a cast to the correct
concrete type: copyObject((Node *)lfirst(cell)).

I was about to update to VS 2026, but now I think I should have an
instance of VS from 2019, 2022, and 2026.

-- 
Bryan Green
EDB: https://www.enterprisedb.com

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Enable test_cplusplusext with MSVC

  2. Disable some C++ warnings in MSVC

  3. meson: Make room for C++-only warning flags for MSVC

  4. Make fixed-length list building macros work in C++

  5. Make unconstify and unvolatize use StaticAssertVariableIsOfTypeMacro

  6. Use typeof everywhere instead of compiler specific spellings

  7. Test List macros in C++ extensions

  8. Test most StaticAssert macros in C++ extensions

  9. Revert "Change copyObject() to use typeof_unqual"

  10. Fix for C++ compatibility

  11. tests: Add a test C++ extension module