Re: [PATCH v1] travis-ci: override CFLAGS properly, add -Wdeclaration-after-statement

From: Jeff King <peff@peff.net>
Date: Feb 8, 2016, 12:25 UTC
Message-ID: <20160208122551.GD24217@sigill.intra.peff.net>
In-Reply-To: <1454921958-53129-1-git-send-email-larsxschneider@gmail.com>

On Mon, Feb 08, 2016 at 09:59:18AM +0100, larsxschneider@gmail.com wrote:

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> From: Lars Schneider <larsxschneider@gmail.com>
> 
> The global Travis-CI environment variable CFLAGS did not override the
> CFLAGS variable in the makefile. Pass CFLAGS as make variable to
> override it properly.

Makes sense.

> In addition to that, add '-Wdeclaration-after-statement' to make a
> Travis-CI build fail (because of '-Werror') if the code does not adhere
> to the Git coding style.

I think this is a good step, but is probably the tip of the iceberg. I typically use:

  -Wall -Werror -Wdeclaration-after-statement
  -Wpointer-arith -Wstrict-prototypes -Wvla
  -Wold-style-declaration -Wold-style-definition

Junio does his integration testing with a similar set, which I think you can find in one of the scripts in his "todo" branch.

> I made this patch because Peff pointed out to me that "git style doesn't
> allow declaration-after-statement" [1]. I wonder if it would make sense
> to add this check even in the makefile [2]?

I think we keep the default CFLAGS to a pretty tame set, so that we build out of the box on a large number of compilers. I know I have run into problems with -Wold-style-* on clang (though perhaps that is no longer the case, as I haven't tried recently), let alone truly antique compilers.

I have, however, wondered if it would make sense to codify this knowledge in the Makefile with an optional knob. E.g., let DEVELOPER=1 roughly mean "you are a git dev, you have a reasonably modern compiler, and want to be as careful as possible before sending your patches".

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> I am no make expert, but I
> also wonder why we don't use the override directive [3] for the CFLAGS?
> AFAIK this would allow a make invocation like this:
> 
> make target CFLAGS+=-Wdeclaration-after-statement

I think it is rather the opposite. If we used:

  override CFLAGS+= ...

in the Makefile, then if a user did:

  make CFLAGS=...

we would add to their CFLAGS (whereas without the override, our appending is ignored). Our Makefile solves that in a different way, though. We pass $(ALL_CFLAGS) to the compiler, and that in turn is made up of $(CFLAGS) and $(BASIC_CFLAGS). We assume the user tweaks the former, and we set the latter based on Makefile knobs (e.g., NO_CURL, etc).

-Peff