From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: Phillip Wood <phillip.wood123@gmail.com>,
git@vger.kernel.org, Collin Funk <collin.funk1@gmail.com>,
Michael J Gruber <git@grubix.eu>
Subject: Re: [PATCH 08/12] skip_prefix(): check const match between in and out params
Date: Wed, 01 Apr 2026 15:13:11 -0700 [thread overview]
Message-ID: <xmqq8qb6uy6g.fsf@gitster.g> (raw)
In-Reply-To: <20260401192423.GA2905896@coredump.intra.peff.net> (Jeff King's message of "Wed, 1 Apr 2026 15:24:23 -0400")
Jeff King <peff@peff.net> writes:
>> > > +#define CONST_OUTPARAM(in, out) \
>> > > + ((const char **)(0 ? ((*(out) = (in)),(out)) : (out)))
>> > > +#define skip_prefix(str, prefix, out) \
>> > > + skip_prefix((str), (prefix), CONST_OUTPARAM((str), (out)))
>> >
>> > This is clever but it changes the behavior of skip_prefix() which is
>> > documented as not touching out if it returns false.
>>
>> Sorry, I've just realized we always take the other branch so this does not
>> change the behavior and is in fact a nice solution to the problem.
>
> Yeah, exactly. I was curious if the dead branch would be left in place,
> but gcc seems to prune it even at -O0.
>
> I also pondered whether:
>
> (*out = in,out)
>
> might be a problem, but I think it is OK. The "," is a sequence point,
> so it is well defined (of course we would never run this code anyway,
> but if we have undefined behavior in the code at all, it may cause
> confusing effects).
Yup, the part I like this the most is that this is still well
defined, and the never-taken side of the ternary will not cause us
trouble.
Very nicely done.
next prev parent reply other threads:[~2026-04-01 22:13 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-31 23:38 [PATCH 0/12] fixing the remainder of the C23 strchr warnings Jeff King
2026-03-31 23:41 ` [PATCH 01/12] convert: add const to fix strchr() warnings Jeff King
2026-03-31 23:41 ` [PATCH 02/12] http: " Jeff King
2026-03-31 23:41 ` [PATCH 03/12] transport-helper: drop " Jeff King
2026-04-01 13:46 ` Patrick Steinhardt
2026-03-31 23:42 ` [PATCH 04/12] pager: explicitly cast away strchr() constness Jeff King
2026-04-01 20:50 ` Junio C Hamano
2026-04-02 3:54 ` Jeff King
2026-03-31 23:42 ` [PATCH 05/12] run-command: explicitly cast away constness when assigning to void Jeff King
2026-03-31 23:44 ` [PATCH 06/12] find_last_dir_sep(): convert inline function to macro Jeff King
2026-03-31 23:46 ` [PATCH 07/12] pseudo-merge: fix disk reads from find_pseudo_merge() Jeff King
2026-03-31 23:56 ` Jeff King
2026-04-01 21:40 ` Junio C Hamano
2026-04-02 23:51 ` Taylor Blau
2026-03-31 23:50 ` [PATCH 08/12] skip_prefix(): check const match between in and out params Jeff King
2026-04-01 13:17 ` Phillip Wood
2026-04-01 14:04 ` Phillip Wood
2026-04-01 19:24 ` Jeff King
2026-04-01 22:13 ` Junio C Hamano [this message]
2026-04-02 15:05 ` Phillip Wood
2026-04-01 13:46 ` Patrick Steinhardt
2026-03-31 23:51 ` [PATCH 09/12] pkt-line: make packet_reader.line non-const Jeff King
2026-04-01 22:18 ` Junio C Hamano
2026-04-02 3:55 ` Jeff King
2026-03-31 23:52 ` [PATCH 10/12] range-diff: drop const to fix strstr() warnings Jeff King
2026-03-31 23:52 ` [PATCH 11/12] http: drop const to fix strstr() warning Jeff King
2026-03-31 23:53 ` [PATCH 12/12] refs/files-backend: drop const to fix strchr() warning Jeff King
2026-04-01 13:46 ` Patrick Steinhardt
2026-04-01 22:22 ` Junio C Hamano
2026-04-02 3:56 ` Jeff King
2026-04-02 4:14 ` [PATCH v2 0/12] fixing the remainder of the C23 strchr warnings Jeff King
2026-04-02 4:14 ` [PATCH v2 01/12] convert: add const to fix strchr() warnings Jeff King
2026-04-02 4:14 ` [PATCH v2 02/12] http: " Jeff King
2026-04-02 4:14 ` [PATCH v2 03/12] transport-helper: drop " Jeff King
2026-04-02 4:14 ` [PATCH v2 04/12] pager: explicitly cast away strchr() constness Jeff King
2026-04-02 4:15 ` [PATCH v2 05/12] run-command: explicitly cast away constness when assigning to void Jeff King
2026-04-02 4:15 ` [PATCH v2 06/12] find_last_dir_sep(): convert inline function to macro Jeff King
2026-04-02 4:15 ` [PATCH v2 07/12] pseudo-merge: fix disk reads from find_pseudo_merge() Jeff King
2026-04-02 4:15 ` [PATCH v2 08/12] skip_prefix(): check const match between in and out params Jeff King
2026-04-02 5:11 ` Junio C Hamano
2026-04-02 6:01 ` Jeff King
2026-04-02 15:50 ` Junio C Hamano
2026-04-02 15:41 ` Junio C Hamano
2026-04-03 11:13 ` Toon Claes
2026-04-04 5:42 ` [PATCH v2 13/12] git-compat-util: fix CONST_OUTPARAM typo and indentation Jeff King
2026-04-02 4:15 ` [PATCH v2 09/12] pkt-line: make packet_reader.line non-const Jeff King
2026-04-02 4:15 ` [PATCH v2 10/12] range-diff: drop const to fix strstr() warnings Jeff King
2026-04-02 4:15 ` [PATCH v2 11/12] http: drop const to fix strstr() warning Jeff King
2026-04-02 4:15 ` [PATCH v2 12/12] refs/files-backend: drop const to fix strchr() warning Jeff King
2026-04-03 11:14 ` [PATCH v2 0/12] fixing the remainder of the C23 strchr warnings Toon Claes
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