[PATCH] cocci: drop bogus xstrdup_or_null() rule

[PATCH] cocci: drop bogus xstrdup_or_null() rule

[Junio C Hamano]

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.

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);

it would probably have been correct.  But there is no existing code
that would have been improved by such a rule, so let's just remove
the bogus one without replacing with the more specific one.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 contrib/coccinelle/xstrdup_or_null.cocci | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/contrib/coccinelle/xstrdup_or_null.cocci b/contrib/coccinelle/xstrdup_or_null.cocci
index 8e05d1ca4b..9c1d2939b6 100644
--- a/contrib/coccinelle/xstrdup_or_null.cocci
+++ b/contrib/coccinelle/xstrdup_or_null.cocci
@@ -1,11 +1,3 @@
-@@
-expression E;
-expression V;
-@@
-- if (E)
--    V = xstrdup(E);
-+ V = xstrdup_or_null(E);
-
 @@
 expression E;
 @@
-- 
2.36.0-233-gea8f06b421

Re: [PATCH] cocci: drop bogus xstrdup_or_null() rule

[Derrick Stolee]

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

Re: [PATCH] cocci: drop bogus xstrdup_or_null() rule

[Junio C Hamano]

Derrick Stolee <derrickstolee@github.com> writes:

> I think you mean if it were
> ...

Please disregard.  That one was completely bogus.

> Dropping the rule makes the most sense.

Yup.  ThHanks for a doze of sanity.