On 11/10/22 15:19, Paul Eggert wrote: > On 2022-11-10 09:16, Zack Weinberg wrote: >> Changes to handle C23 built-in ‘bool’ better are under development but >> the design has not yet been finalized. > > [I'm cc'ing this to bug-gnulib too.] > > To my mind this is the biggest outstanding issue in Autoconf as far as > C23 goes, as the upgrade path for Autoconf's existing bool support is > not entirely clear. As Florian mentioned, distros can't assume Autoconf > upgrades when building other packages; that being said, we should get > Autoconf's bool support fixed sooner rather than later as bool hassles > will remain until Autoconf is fixed and these fixes are propagated to > Autoconf's users. > > Here's the main Autoconf issue issue with bool. Traditionally, Autoconf > supported K&R C, C89, C99, etc. At some point (I'm not sure when), > Autoconf started requiring C89 or later. Is it now OK for Autoconf to > require C99 or later, as far as bool is concerned? If so, that'll > considerably simplify the ongoing maintenance hassle for bool. > > Requiring C99-or-later bool is the option that Gnulib has taken. Its > 'stdbool' module and its gl_C_BOOL macro assumes C99 or later, and as > far as I know no Gnulib-using package is using Gnulib's 'stdbool-c99' > module which we kept around in case somebody still needed bool to work > atop a C89 system. (We considered supporting C23 bool atop C89 but it > was too painful.) I am fine with this option. > If we follow Gnulib's lead, Autoconf will generate a config.h that does > "#include <stdbool.h>" on pre-C23 systems At least in the case of config.h files that could be included in external programs, I recommend unconditionally generating “#include <stdbool.h>”. That will ensure pre-C23 code that includes these headers builds okay. I believe that in C23 and above this is a harmless no-op, as it is in C++. > and this config.h will not > not work on pre-C99 systems. This of course could in theory break some > programs, just as compiling them with C23 can break them. But I don't > see any better option at this point. And besides, what package outside > of a museum still requires C89 and don't work with C99? I just checked and both GCC 12.2 and clang 14 support <stdbool.h> in C89 mode. I do get a -Wc99-extensions warning from clang but that can easily be suppressed with -Wno-c99-extensions. -- Sincerely, Demi Marie Obenour (she/her/hers)
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