On Sat, Aug 07, 2021 at 04:56:04AM +0200, Ævar Arnfjörð Bjarmason wrote: > > On Sat, Aug 07, 2021 at 04:02:45AM +0200, Ævar Arnfjörð Bjarmason wrote: > > > >> Perhaps I've missed some obvious reason not to do this, but why are we > >> parsing the --version output of two modern compilers, as opposed to just > >> asking them what type/version they are via their usual macro facilities? > >> I.e. something like the below: > > > > That would probably work OK in practice, but it actually seems more > > complex to me (how do other random compilers react to "-E -"? > > We only care about gcc and clang in that script, which I think have > supported that form of "-E" on stdin input for any version we're likely > to care about for the purposes of config.mak.dev. It seems unlikely that > we'll care about non-modern compilers in config.mak.dev, so using more > modern features there seems fine (it's all for opting us into even more > modern warning flags and the like...). Yeah, but we don't find out what we have until we run the script in question. I guess it is OK as long as we redirect stderr, ignore the exit code, and only look for a positive outcome in the output (your patch does the latter two already). I also wondered how this might interact with CC="ccache gcc" (where caching might fail to notice version changes). But from some quick testing, it looks like it doesn't cache in this case (neither stdin, nor with -E). > > Is it possible for us to get other output from the preprocessor that > > would confuse an eval?). > > Probably, I just meant that as a POC. We could pipe it into some > awk/grep/cut/perl or whatever that would be more strict. That would probably be better. I would be curious to hear from somebody with a mac if this technique gives more sensible version numbers for the Apple-clang compiler. -Peff
