New versions of perl trigger warnings within perl.h with our compiler
flags. At least -Wdeclaration-after-statement, -Wshadow=compatible-local are
known to be problematic.
To avoid these warnings, conditionally use #pragma GCC system_header before
including plperl.h.
Alternatively, we could add the include paths for problematic headers with
-isystem, but that is a larger hammer and is harder to search for.
A more granular alternative would be to use #pragma GCC diagnostic
push/ignored/pop, but gcc warns about unknown warnings being ignored, so every
to-be-ignored-temporarily compiler warning would require its own pg_config.h
symbol and #ifdef.
As the warnings are voluminous, it makes sense to backpatch this change. But
don't do so yet, we first want gather buildfarm coverage - it's e.g. possible
that some compiler claiming to be gcc compatible has issues with the pragma.
Author: Andres Freund <andres@anarazel.de>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: Discussion: https://postgr.es/m/20221228182455.hfdwd22zztvkojy2@awork3.anarazel.de
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