[PATCH 2/2] gcc8.1: fix strcat warning

[John Keeping]

On Wed, Jun 13, 2018 at 07:34:07AM +0800, Andy Green wrote:
> ../ui-ssdiff.c: In function ‘replace_tabs’:
> ../ui-ssdiff.c:142:4: warning: ‘strncat’ output truncated copying between 1 and 8 bytes from a string of length 8 [-Wstringop-truncation]
>     strncat(result, spaces, 8 - (strlen(result) % 8));
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Actually the strncat that was there before intends that its
> stock of spaces gets truncated, and it's not a problem.
> 
> However gcc8.1 is also right, normally truncation is undesirable.
> 
> Make the code do the padding explicitly.
> 
> Signed-off-by: Andy Green <andy at warmcat.com>

Reviewed-by: John Keeping <john at keeping.me.uk>

> ---
>  ui-ssdiff.c |   12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/ui-ssdiff.c b/ui-ssdiff.c
> index 7f261ed..e520b95 100644
> --- a/ui-ssdiff.c
> +++ b/ui-ssdiff.c
> @@ -118,7 +118,6 @@ static char *replace_tabs(char *line)
>  	int n_tabs = 0;
>  	int i;
>  	char *result;
> -	char *spaces = "        ";
>  
>  	if (linelen == 0) {
>  		result = xmalloc(1);
> @@ -138,8 +137,17 @@ static char *replace_tabs(char *line)
>  			strcat(result, prev_buf);
>  			break;
>  		} else {
> +			char *p;
> +			int n;
> +
>  			strncat(result, prev_buf, cur_buf - prev_buf);
> -			strncat(result, spaces, 8 - (strlen(result) % 8));
> +
> +			n = strlen(result);
> +			p = result + n;
> +			n = 8 - (n % 8);
> +			while (n--)
> +				*p++ = ' ';
> +			*p = '\0';
>  		}
>  		prev_buf = cur_buf + 1;
>  	}
>