Re: [PATCH v2] doc: document and test `@` prefix for raw timestamps

[Junio C Hamano <gitster@pobox.com>]

Luna Schwalbe <dev@luna.gl> writes:

> The Git internal date format `<unix-timestamp> <time-zone-offset>`
> fails to parse when the timestamp is less than 100,000,000 (fewer than
> 9 digits). This happens to avoid potential ambiguity with other date
> formats such as `YYYYMMDD`, especially when used with approxidate.
>
> To force the parser to interpret the value as a raw timestamp, it must
> be prefixed with `@` (e.g., `@0 +0000`). This behavior was introduced
> in 2c733fb24c10a9d7aacc51f956bf9b7881980870 (parse_date(): '@' prefix
> forces git-timestamp, 2012-02-02) but was never documented.
>
> Document the `@` prefix in `Documentation/date-formats.adoc` to make
> this behavior explicit. Also add test cases to `t/t0006-date.sh` to
> verify and demonstrate the difference between prefixed and unprefixed
> small timestamps (e.g., `@2000` vs `2000`).
>
> Signed-off-by: Luna Schwalbe <dev@luna.gl>
> Co-authored-by: Junio C Hamano <gitster@pobox.com>
> ---
> Fixed the asciidoc formatting, removed parens around YYYYMMDD example.

Looks good.

Next time, when sending a [v2] patch of a singleton topic,
please make it a reply e-mail message to the [v1] message.  That
would make it easier to see how patches evolved in mailing list
archive.  E.g., https://lore.kernel.org/git/$message_id would show
both rounds (including the review comments they received) on the
same page.

Will queue.  Thanks.



>  Documentation/date-formats.adoc |  5 +++++
>  t/t0006-date.sh                 | 11 +++++++++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/Documentation/date-formats.adoc b/Documentation/date-formats.adoc
> index e24517c49..330424b2b 100644
> --- a/Documentation/date-formats.adoc
> +++ b/Documentation/date-formats.adoc
> @@ -9,6 +9,11 @@ Git internal format::
>  	`<unix-timestamp>` is the number of seconds since the UNIX epoch.
>  	`<time-zone-offset>` is a positive or negative offset from UTC.
>  	For example CET (which is 1 hour ahead of UTC) is `+0100`.
> ++
> +It is safer to prepend the `<unix-timestamp>` with `@` (e.g.,
> +`@0 +0000`), which forces Git to interpret it as a raw timestamp. This
> +is required for values less than 100,000,000 (which have fewer than 9
> +digits) to avoid confusion with other date formats like `YYYYMMDD`.
>  
>  RFC 2822::
>  	The standard date format as described by RFC 2822, for example
> diff --git a/t/t0006-date.sh b/t/t0006-date.sh
> index 53ced36df..8b4e1870b 100755
> --- a/t/t0006-date.sh
> +++ b/t/t0006-date.sh
> @@ -138,6 +138,13 @@ check_parse '1969-12-31 23:59:59 Z' bad
>  check_parse '1969-12-31 23:59:59 +11' bad
>  check_parse '1969-12-31 23:59:59 -11' bad
>  
> +# pathologically small timestamps requiring `@` prefix
> +check_parse '@0 +0000' '1970-01-01 00:00:00 +0000'
> +check_parse '@99999999 +0000' '1973-03-03 09:46:39 +0000'
> +check_parse '99999999 +0000' bad
> +check_parse '@100000000 +0000' '1973-03-03 09:46:40 +0000'
> +check_parse '100000000 +0000' '1973-03-03 09:46:40 +0000'
> +
>  REQUIRE_64BIT_TIME=HAVE_64BIT_TIME
>  check_parse '2099-12-31 23:59:59' '2099-12-31 23:59:59 +0000'
>  check_parse '2099-12-31 23:59:59 +00' '2099-12-31 23:59:59 +0000'
> @@ -195,6 +202,10 @@ check_approxidate '6AM, June 7, 2009' '2009-06-07 06:00:00'
>  check_approxidate '2008-12-01' '2008-12-01 19:20:00'
>  check_approxidate '2009-12-01' '2009-12-01 19:20:00'
>  
> +# ambiguous raw timestamp
> +check_approxidate '2000 +0000' '2000-08-30 19:20:00'
> +check_approxidate '@2000 +0000' '1970-01-01 00:33:20'
> +
>  check_date_format_human() {
>  	t=$(($GIT_TEST_DATE_NOW - $1))
>  	echo "$t -> $2" >expect