Subject: Re: [PATCH] am: fix condition check on fseek

From: Junio C Hamano <[email-masked]>
Date: Mon, 23 Sep 2024 09:43:09 -0700

"Kristoffer Haugsbakk" <[email-masked]> writes:

> On Sat, Sep 21, 2024, at 17:08, Ruffalo Lavoisier wrote:
>> if fseek() is success, return value is 0
>>
>> Signed-off-by: Ruffalo Lavoisier <[email-masked]>
>> ---
>>  builtin/am.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/builtin/am.c b/builtin/am.c
>> index d8875ad402..a7727fd4ea 100644
>> --- a/builtin/am.c
>> +++ b/builtin/am.c
>> @@ -589,7 +589,7 @@ static int is_mail(FILE *fp)
>>  	regex_t regex;
>>  	int ret = 1;
>>
>> -	if (fseek(fp, 0L, SEEK_SET))
>> +	if (!fseek(fp, 0L, SEEK_SET))
>>  		die_errno(_("fseek failed"));
>>
>>  	if (regcomp(&regex, header_regex, REG_NOSUB | REG_EXTENDED))
>> --
>> 2.46.1
>
> I don’t get this change? The function returns false on success. true if
> it fails (not zero). You want the program to die if it returns non-zero.
>
> It’s hard to wrap my head around… “false must mean “no errors” ”
>
> If the original code has a bug then I don’t see how git-am(1) could work
> considering it presumably always checks ‘is_mail’.

Yeah, the proposed log message states a correct fact, but it is
unclear how that justifies the change in the patch part of the
message.