Re: Change copyObject() to use typeof_unqual

On 20.01.26 10:37, Peter Eisentraut wrote:
> Currently, when the argument of copyObject() is const-qualified, the 
> return type is also, because the use of typeof carries over all the 
> qualifiers.  This is incorrect, since the point of copyObject() is to 
>   make a copy to mutate.  But apparently no code ran into it.
> 
> The new implementation uses typeof_unqual, which drops the qualifiers, 
> making this work correctly.
> 
> typeof_unqual is standardized in C23, but all recent versions of all the 
> usual compilers support it even in non-C23 mode, at least as 
> __typeof_unqual__.  We add a configure/meson test for typeof_unqual and 
> __typeof_unqual__ and use it if it's available, else we use the existing 
> fallback of just returning void *.

I committed this first part, but it ran into some trouble on the buildfarm:

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=taipan&dt=2026-02-04%2008%3A39%3A34

The problem is that configure detected that gcc supports typeof_unqual, 
but the clang used to produce the .bc files does not.

This seems to be a possible problem in general, if we do all these 
configure checks with $CC, but then run $CLANG assuming all the results 
hold.

My first attempt to fix this was to set CLANG='clang -std=gnu23' to 
effectively put clang into approximately the same mode as gcc.  This 
fixes this particular issue but then later fails when compiling .bc 
files for the test_cplusplus module:

clang -std=gnu23 -xc++ -Wno-ignored-attributes -O2  -I. -I. 
-I../../../../src/include -D_GNU_SOURCE  -I/usr/include/libxml2 
-flto=thin -emit-llvm -c -o test_cplusplusext.bc test_cplusplusext.cpp
error: invalid argument '-std=gnu23' not allowed with 'C++'

This might be another looming problem.  Do we need to look up, say, 
CLANGXX separately from CLANG?

Another attempt was to switch the order of the configure test to check 
for __typeof_unqual__ before typeof_unqual.  This works, but it seems 
totally unprincipled.

Any thoughts?

(Btw., the buildfarm member description says gcc 13, but it's actually 
using gcc 15.)