Re: [PATCH] Makefile: make COMPUTE_HEADER_DEPENDENCIES=auto work with DEVOPTS=pedantic
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Sep 22, 2021, 16:08 UTC
- Message-ID
- <xmqqmto48ufz.fsf@gitster.g>
- In-Reply-To
- <patch-1.1-6b2e9af5e67-20210922T103749Z-avarab@gmail.com>
Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
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> The "COMPUTE_HEADER_DEPENDENCIES" feature added in [1] was extended to > use auto-detection in [2]. Then when -Wpedantic support was added to > DEVOPTS in [3] we started passing -Wpedantic in combination with > -Werror to the compiler here. > > This broke the auto-detection, but since we'd quieted it in [4] we > didn't find out.
Are the references correct? I am not seeing "quiet"ing in [4]. The redirection 2>&1 to cram error messages also to $(dep_check), hence making it impossible to match '0', was done in [2].
We did make the pedantic mode the default and pass both -pedantic and -Wpedantic after [4]. Before we had only -pedantic.
Show 16 quoted lines
> It was emitting all of this on STDERR under GCC: > > /dev/null:1: error: ISO C forbids an empty translation unit > [-Werror=pedantic] > cc1: note: unrecognized command-line option > ‘-Wno-pedantic-ms-format’ may have been intended to silence > earlier diagnostics > cc1: all warnings being treated as errors > > Let's fix that bug by maintaining a NON_DEVELOPER_CFLAGS, it's like > ALL_CFLAGS but without anything we add in config.mak.dev, and > furthermore stop redirecting STDERR to /dev/null, this means that > someone whose compiler doesn't support this will see this output, but > also this new message: > > Non-zero 1 exit with COMPUTE_HEADER_DEPENDENCIES=auto, set it to "yes" or "no" to quiet auto-detect
Hmmmmmph.
I recentaly saw many .depend directories (not necessarily empty) left after "make distclean". After building on one branch, I often check out a different branch then run distclean on the new branch, so leftover build artifacts are not necessarily a bug in our Makefile, but the bug you found may explain it?
While I agree with your analysis of the problem, I cannot shake this nagging feeling that the proposed solution is barking up a wrong tree. After all, -pedantic and any other option that lets the compiler notice that it is being asked to compile an empty source can come directly from the end user (e.g. CC="gcc -pedantic" or as part of CFLAGS)---realization of which makes me wonder if it is essential to compile /dev/null for this check, or any reasonably syntactically correct program would do.
I wonder if the attached (with clean-up to remove the tracing cruft) would show us a better direction. It feeds a single line
int dummy_for_dep_check;
C "program" from the standard input of the compiler to tackle the "you are not supposed to be compiling an empty compilation unit" problem in a more direct way.
Makefile | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git c/Makefile w/Makefile index 9df565f27b..0593ab7287 100644 --- c/Makefile +++ w/Makefile @@ -1277,9 +1277,9 @@ COMPUTE_HEADER_DEPENDENCIES = auto endif ifeq ($(COMPUTE_HEADER_DEPENDENCIES),auto) -dep_check = $(shell $(CC) $(ALL_CFLAGS) \ +dep_check = $(shell echo >&2 doing dep check; echo int dummy_for_dep_check\; | $(CC) $(ALL_CFLAGS) \ -c -MF /dev/null -MQ /dev/null -MMD -MP \ - -x c /dev/null -o /dev/null 2>&1; \ + -x c - -o /dev/null || echo >&2 oops; \ echo $$?) ifeq ($(dep_check),0) override COMPUTE_HEADER_DEPENDENCIES = yes