On Sat, Aug 07, 2021 at 04:56:04AM +0200, Ævar Arnfjörð Bjarmason wrote:

quoted

On Sat, Aug 07, 2021 at 04:02:45AM +0200, Ævar Arnfjörð Bjarmason wrote:

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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).

quoted

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