Subject: Re: [PATCH] fetch: convert strncmp() with strlen() to starts_with()

From: Junio C Hamano <[email-masked]>
Date: Mon, 26 Feb 2024 09:11:55 -0800

Junio C Hamano <[email-masked]> writes:

>> -		     !strncmp(rs->items[i].src,
>> -			      ref_namespace[NAMESPACE_TAGS].ref,
>> -			      strlen(ref_namespace[NAMESPACE_TAGS].ref)))) {
>> +		     starts_with(rs->items[i].src,
>> +				 ref_namespace[NAMESPACE_TAGS].ref))) {
>
> The original tries to check that "namespace" fully matches the
> initial part of .src string, which is exactly what starts_with()
> does.  Makes sense.

There are two more such instances in the codebase, easily found with

        $ cat >contrib/coccinelle/starts_with.cocci <<\-EOF
        @@
        expression string, prefix;
        @@
        - !strncmp(string, prefix, strlen(prefix))
        + starts_with(string, prefix)

        @@
        expression string, prefix;
        @@
        - strncmp(string, prefix, strlen(prefix))
        + !starts_with(string, prefix)
        EOF
        $ make contrib/coccinelle/starts_with.cocci.patch

which finds the one you just fixed (naturally, since the Cocci patch
was written by taking inspiration from your fix).

Here is one in the reftable code.  The other one is in xdiff/ I'd
rather not touch (as starts_with() is probably not available there).

diff -u -p a/reftable/refname.c b/reftable/refname.c
--- a/reftable/refname.c
+++ b/reftable/refname.c
@@ -103,7 +103,7 @@ static int modification_has_ref_with_pre
 			}
 		}
 
-		if (strncmp(ref.refname, prefix, strlen(prefix))) {
+		if (!starts_with(ref.refname, prefix)) {
 			err = 1;
 			goto done;
 		}