Re: [PATCH] Makefile: make COMPUTE_HEADER_DEPENDENCIES=auto work with DEVOPTS=pedantic

>
> Jeff King <peff@peff.net> writes:
>
> >> 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.
> >
> > That feels a bit like we're playing a game of chicken with the compiler
> > in terms of what it may complain about. For example, sparse will
> > complain:
> >
> >   foo.c:1:5: warning: symbol 'dummy_for_dep_check' was not declared. Should it be static?
> >
> > Might compilers ever learn to warn of the same thing?
>
> Certainly.  That is the reason why I said "direction", not
> "solution", and I do not think it is beyond our capability to come
> up with a minimal "C program" that would be lint clean to make it
> as a part of the "solution".
>
> For example, would sparse or compilers complain about this?
>
>     extern int incr(int); int incr(int i) { return i + 1; }
>
> > So I'd argue we should go even simpler, like:
> >
> > diff --git a/Makefile b/Makefile
> > index 3628d14f16..4597a126d0 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1277,7 +1277,7 @@ COMPUTE_HEADER_DEPENDENCIES = auto
> >  endif
> >
> >  ifeq ($(COMPUTE_HEADER_DEPENDENCIES),auto)
> > -dep_check = $(shell $(CC) $(ALL_CFLAGS) \
> > +dep_check = $(shell $(CC) \
> >       -c -MF /dev/null -MQ /dev/null -MMD -MP \
> >       -x c /dev/null -o /dev/null 2>&1; \
> >       echo $$?)
>
> I am all for this simplification.  It takes us back to the state
> before 1816bf26 (Makefile: Improve compiler header dependency check,
> 2011-08-30).  But I think that is more or less orthogonal to the
> "you are not supposed to feed an empty compilation unit" issue.