From: Jeff King <peff@peff.net>
Date: Tue, 14 Apr 2020 20:24:01 GMT
Subject: Re: [PATCH 2/2] date.c: allow compact version of ISO-8601 datetime
Message-ID: <20200414202401.GC1879688@coredump.intra.peff.net>
In-Reply-To: <06e62c58d5accad7bbebbc51f9fb38fda83a73f6.1586856398.git.congdanhqx@gmail.com>

On Tue, Apr 14, 2020 at 04:31:55PM +0700, Đoàn Trần Công Danh wrote:

> @@ -666,6 +666,24 @@ static int match_digit(const char *date, struct tm *tm, int *offset, int *tm_gmt
>  		n++;
>  	} while (isdigit(date[n]));
>  
> +	/* 8 digits, compact style of ISO-8601's date: YYYYmmDD */
> +	if (n == 8) {
> +		tm->tm_year = num / 10000 - 1900;
> +		tm->tm_mon = (num % 10000) / 100 - 1;
> +		tm->tm_mday = num % 100;
> +		return n;
> +	}

I worry a little this may conflict with other approxidate heuristics.
The only one I can think of is an actual unix timestamp, though, and we
already require that to have at least 9 digits (plus anybody wanting to
use one robustly really should be using @12345678).

And it looks like we'd exit early from the function for anything longer
than 4 digits anyway, ignoring the value.

We could probably tighten the heuristics a bit by insisting that the
month and day be sensible. Or even year (see the 1900 to 2100 magic for
the 4-digit year guess).

> +	/* 6 digits, compact style of ISO-8601's time: HHMMSS */
> +	if (n == 6) {
> +		tm->tm_hour = num / 10000;
> +		tm->tm_min = (num % 10000) / 100;
> +		tm->tm_sec = num % 100;
> +		if (*end == '.' && isdigit(end[1]))
> +			strtoul(end + 1, &end, 10);
> +		return end - date;
> +	}

And likewise here that the hour, minute, and second be reasonable.

-Peff