Re: [PATCH 2/3] reftable: remove unreachable "return" statements

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Hi Ævar,

On Thu, 13 Jan 2022, Ævar Arnfjörð Bjarmason wrote:

> On Wed, Jan 12 2022, Taylor Blau wrote:
>
> > On Wed, Jan 12, 2022 at 01:47:40PM +0100, Ævar Arnfjörð Bjarmason wrote:
> >> >> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> >> >> ---
> >> >>  reftable/refname.c | 1 -
> >> >>  reftable/writer.c  | 1 -
> >> >>  2 files changed, 2 deletions(-)
> >> >>
> >> >> diff --git a/reftable/refname.c b/reftable/refname.c
> >> >> index 95734969324..136001bc2c7 100644
> >> >> --- a/reftable/refname.c
> >> >> +++ b/reftable/refname.c
> >> >> @@ -132,7 +132,6 @@ static int validate_refname(const char *name)
> >> >>  			return REFTABLE_REFNAME_ERROR;
> >> >>  		name = next + 1;
> >> >>  	}
> >> >> -	return 0;
> >> >>  }
> >> >
> >> > In this case the loop inside of validate_refname() should always
> >> > terminate the function within the loop body. But removing this return
> >> > statement here relies on the compiler to determine that fact.
> >> >
> >> > I could well imagine on the other end of the spectrum there exists a
> >> > compiler which _doesn't_ make this inference pass, and would complain
> >> > about the opposite thing as you're reporting from SunCC (i.e., that this
> >> > function which returns something other than void does not have a return
> >> > statement outside of the loop).
> >> >
> >> > So in that sense, I disagree with the guidance of SunCC's warning. In
> >> > other words: by quelching this warning under one compiler, are we
> >> > introducing a new warning under a different/less advanced compiler?
> >>
> >> I'd think that any compiler who'd warn about this sort of thing at all
> >> would be able to spot constructs like this one, which are basically:
> >>
> >>     while (1) {
> >>     	...
> >>         if (x)
> >>         	return;
> >> 	...
> >>     }
> >>     return; /* unreachable */
> >>
> >> Where the elided code contains no "break", "goto" or other mechanism for
> >> exiting the for-loop.
> >>
> >> I.e. GCC and Clang don't bother to note the unreachable code, but I
> >> don't think the reverse will be true, that a compiler will say that a
> >> "return" is missing there. Having a function be just a loop body that
> >> returns an some point is a common pattern.
> >
> > Right, but I'm more concerned about a less advanced compiler that would
> > complain about the absence of a `return` statement as the last
> > instruction in a non-void function.
> >
> > This is probably all academic, anyway, since less advanced compilers
> > probably have other issues compiling Git as it stands today, but
> > fundamentally I think that SunCC's warnings here are at the very least
> > inconsiderate of less advanced compilers.
> >
> > To me, the safest thing to do would be to leave the code as-is and drop
> > this patch.
>
> I really don't see that, sorry. We have an actual example of a compliler
> that does emit a warning new in this rc on this code, but AFAICT your
> concern is purely hypothetical.

It's just a warning.

So I concur with Taylor. This patch does not need to go into v2.35.0.

Ciao,
Johannes