From: Derrick Stolee <derrickstolee@github.com>
To: Junio C Hamano <gitster@pobox.com>, git@vger.kernel.org
Subject: Re: [PATCH] cocci: drop bogus xstrdup_or_null() rule
Date: Mon, 2 May 2022 09:46:11 -0400 [thread overview]
Message-ID: <4181f814-6d8e-ff2c-6fc9-a625ac189eae@github.com> (raw)
In-Reply-To: <xmqq1qxd6e4x.fsf@gitster.g>
On 5/1/2022 1:00 AM, Junio C Hamano wrote:
> 13092a91 (cocci: refactor common patterns to use xstrdup_or_null(),
> 2016-10-12) introduced a rule to rewrite this conditional call to
> xstrdup(E) and an assignment to variable V:
>
> - if (E)
> - V = xstrdup(E);
>
> into an unconditional call to xstrdup_or_null(E) and an assignment
> to variable V:
>
> + V = xstrdup_or_null(E);
>
> which is utterly bogus. The original code may already have an
> acceptable value in V and the conditional assignment may be to
> improve the value already in V with a copy of a better value E when
> (and only when) E is not NULL.
Yes, this makes sense.
> The rewritten construct unconditionally discards the existing value
> of V and replaces it with a copy of E, even when E is NULL, which
> changes the meaning of the program.
>
> By the way, if it were
>
> -if (E && !V)
> - V = xstrdup(E);
> +V = xstrdup_or_null(E);
I think you mean if it were
-if (E && !V)
- V = xstrdup(E);
+if (!V)
+ V = xstrdup_or_null(E);
or
-if (E && !V)
- V = xstrdup(E);
+free(V);
+V = xstrdup_or_null(E);
But yes, there is no preimage matching this pattern, so it
doesn't matter.
Dropping the rule makes the most sense.
Thanks,
-Stolee
next prev parent reply other threads:[~2022-05-02 13:46 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-01 5:00 [PATCH] cocci: drop bogus xstrdup_or_null() rule Junio C Hamano
2022-05-02 13:46 ` Derrick Stolee [this message]
2022-05-02 17:07 ` Junio C Hamano
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