Re: [PATCH] Makefile: detect compiler and enable more warnings in DEVELOPER=1

[Jeff King <peff@peff.net>]

On Sun, Mar 18, 2018 at 09:18:34AM +0100, Nguyễn Thái Ngọc Duy wrote:

> The set of extra warnings we enable when DEVELOPER has to be
> conservative because we can't assume any compiler version the
> developer may use. Detect the compiler version so we know when it's
> safe to enable -Wextra and maybe more.

Hrm, I was planning to expand my patch into a series. In particular, in
my experiments some of those warnings do not need to be disabled under
-Wextra (I tested going back to gcc 5 and clang 4.0).

I think it's worth splitting up the boilerplate changes from the
decisions on individual warnings, because I suspect we'll need to revise
the latter going forward.

I also noticed that all of those options seem to go back at least to
gcc-5. It makes me wonder how much we even need this version-detecting
framework. There are one or two "clang vs gcc" things I've found, but I
haven't found a case where old versions of gcc don't support a
particular option.

IOW, could we get away with just adding these to the DEVELOPER knob and
assuming that people who use it have a reasonably modern gcc or clang
setup? That's more or less what the existing knobs do.

But I didn't follow whether there was any earlier discussion on specific
problems.

>  -dumpversion does not work correctly for clang. So I use "-v" instead
>  which seems to produce the same output for both gcc and clang (with a
>  minor difference in freebsd where it says "FreeBSD clang" instead of
>  just "clang"). Not sure if it helps your "cc on debian" case though

Heh. At first I was confused, as it seems to work for me:

  $ clang-4.0 -dumpversion
  4.2.1

But then I tried this:

  $ clang-5.0 -dumpversion
  4.2.1

Whoops. It returns the same value up through clang 7.

-Peff