Hi, On 2022-11-02 17:03:34 -0700, Andres Freund wrote: > On 2022-11-02 19:57:45 -0400, Tom Lane wrote: > > Andres Freund <and...@anarazel.de> writes: > > > On 2022-11-01 17:00:27 -0400, Peter Eisentraut wrote: > > >> Python has the same issues. There are a few other Python-embedding > > >> projects > > >> that use -Wdeclaration-after-statement and complain if the Python headers > > >> violate it. But it's getting tedious. -isystem would be a better > > >> solution. > > > > > Which dependencies should we convert to -isystem? > > > > Color me confused about what's being discussed here. I see nothing > > in the gcc manual suggesting that -isystem has any effect on warning > > levels? > > It's only indirectly explained :( > > The -isystem and -idirafter options also mark the directory as a > system directory, so that it gets the same special treatment that is applied > to > the standard system directories. > > and then https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html
The attached *prototype* patch is a slightly different spin on the idea of using -isystem: It adds a #pragma GCC system_header to plperl.h if supported by the compiler. That also avoids warnings from within plperl and subsidiary headers. I don't really have an opinion about whether using the pragma or -isystem is preferrable. I chose the pragma because it makes it easier to grep for headers where we chose to do this. I added the pragma detection only to the meson build, but if others think this is a good way to go, I'll do the necessary autoconf wrangling as well. In the compiler test, I chose to not check whether -Werror=unknown-pragmas is supported - it appears to be an old gcc flag, and the worst outcome is that HAVE_PRAGMA_SYSTEM_HEADER isn't defined. We could alternatively define HAVE_PRAGMA_SYSTEM_HEADER or such based on __GNUC__ being defined. Greetings, Andres Freund
>From ee6d9760206b59baa8f2d9adb09cf730ca2d24a4 Mon Sep 17 00:00:00 2001 From: Andres Freund <and...@anarazel.de> Date: Wed, 28 Dec 2022 10:09:48 -0800 Subject: [PATCH] wip: perl: If supported, use gcc's system_header pragma to hide warnings Author: Reviewed-by: Discussion: https://postgr.es/m/ Backpatch: --- meson.build | 9 +++++++++ src/pl/plperl/plperl.h | 8 ++++++++ 2 files changed, 17 insertions(+) diff --git a/meson.build b/meson.build index b872470cdfe..1532b04c62a 100644 --- a/meson.build +++ b/meson.build @@ -1408,6 +1408,15 @@ if not cc.compiles(c99_test, name: 'c99', args: test_c_args) endif endif +# Does the compiler support #pragma GCC system_header? We optionally use it to +# avoid warnings that we can't fix (e.g. in the perl headers). +# See https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html +if cc.compiles('#pragma GCC system_header', + name: 'pragma system header', + args: test_c_args + ['-Werror=unknown-pragmas']) + cdata.set('HAVE_PRAGMA_SYSTEM_HEADER', 1) +endif + sizeof_long = cc.sizeof('long', args: test_c_args) cdata.set('SIZEOF_LONG', sizeof_long) if sizeof_long == 8 diff --git a/src/pl/plperl/plperl.h b/src/pl/plperl/plperl.h index 5243f308bd5..2656a0376ee 100644 --- a/src/pl/plperl/plperl.h +++ b/src/pl/plperl/plperl.h @@ -74,6 +74,14 @@ #define HAS_BOOL 1 #endif +/* + * At least in newer versions the perl headers trigger a lot of warnings with + * our compiler flags. The system_header pragma hides warnings from within the + * rest of this file, if supported. + */ +#if HAVE_PRAGMA_SYSTEM_HEADER +#pragma GCC system_header +#endif /* * Get the basic Perl API. We use PERL_NO_GET_CONTEXT mode so that our code -- 2.38.0
