[RFC PATCH] approxidate: make "today" wrap to midnight

[RFC PATCH] approxidate: make "today" wrap to midnight

[Tuomas Ahola]

Although some commands do reject invalid approxidate expressions,
in other cases those are simply evaluated as the current time.
Oftentimes that is a perfectly good compromise to handle silly
requests, but it isn't without rough edges.

Let's consider what "git log --since=today" should yield.
As it happens that "today" isn't actually a valid approxidate
format, the command currently tries to list commits with
*future* timestamps.  Perhaps it would make more sense if
it returned the commits made since midnight---that is,
during the current day.

Moreover, a revision parameter "@{today}" is currently outright
rejected.  Making "today" a valid approxidate time format could
make a natural way to specify the state of the ref at the start
of the current day.

Bind "today" to new function `date_today()` as an approxidate
special.  Make it return the last midnight if no specific time
is given; i.e. retain the old behavior of "noon today" and such.

Signed-off-by: Tuomas Ahola <taahol@utu.fi>
---

Notes:
    The "Jan 5 today" test is adapted from
    
      c27cc94fad (approxidate: handle pending number for "specials", 2018-11-02):
    
    > (saying "Jan 5 yesterday" should not respect the number at all).

 date.c          | 10 ++++++++++
 t/t0006-date.sh |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/date.c b/date.c
index 17a95077cf..343d6aab6f 100644
--- a/date.c
+++ b/date.c
@@ -1192,6 +1192,15 @@ static void date_never(struct tm *tm, struct tm *now UNUSED, int *num)
 	*num = 0;
 }
 
+static void date_today(struct tm *tm, struct tm *now, int *num UNUSED)
+{
+	if (tm->tm_hour == now->tm_hour &&
+	    tm->tm_min == now->tm_min &&
+	    tm->tm_sec == now->tm_sec)
+		date_time(tm, now, 0);
+	update_tm(tm, now, 0);
+}
+
 static const struct special {
 	const char *name;
 	void (*fn)(struct tm *, struct tm *, int *);
@@ -1204,6 +1213,7 @@ static const struct special {
 	{ "AM", date_am },
 	{ "never", date_never },
 	{ "now", date_now },
+	{ "today", date_today },
 	{ NULL }
 };
 
diff --git a/t/t0006-date.sh b/t/t0006-date.sh
index 53ced36df4..07bf6115ab 100755
--- a/t/t0006-date.sh
+++ b/t/t0006-date.sh
@@ -164,6 +164,7 @@ check_approxidate() {
 }
 
 check_approxidate now '2009-08-30 19:20:00'
+check_approxidate today '2009-08-30 00:00:00'
 check_approxidate '5 seconds ago' '2009-08-30 19:19:55'
 check_approxidate 5.seconds.ago '2009-08-30 19:19:55'
 check_approxidate 10.minutes.ago '2009-08-30 19:10:00'
@@ -187,6 +188,7 @@ check_approxidate 'last tuesday' '2009-08-25 19:20:00'
 check_approxidate 'July 5th' '2009-07-05 19:20:00'
 check_approxidate '06/05/2009' '2009-06-05 19:20:00'
 check_approxidate '06.05.2009' '2009-05-06 19:20:00'
+check_approxidate 'Jan 5 today' '2009-01-30 00:00:00'
 
 check_approxidate 'Jun 6, 5AM' '2009-06-06 05:00:00'
 check_approxidate '5AM Jun 6' '2009-06-06 05:00:00'

base-commit: 94f057755b7941b321fd11fec1b2e3ca5313a4e0
-- 
2.30.2

Re: [RFC PATCH] approxidate: make "today" wrap to midnight

[Junio C Hamano]

Tuomas Ahola <taahol@utu.fi> writes:

> Although some commands do reject invalid approxidate expressions,
> in other cases those are simply evaluated as the current time.
> Oftentimes that is a perfectly good compromise to handle silly
> requests, but it isn't without rough edges.
>
> Let's consider what "git log --since=today" should yield.
> As it happens that "today" isn't actually a valid approxidate
> format, the command currently tries to list commits with
> *future* timestamps.  Perhaps it would make more sense if
> it returned the commits made since midnight---that is,
> during the current day.

I actually am of two minds about this.  

What should "git log --until=today" do when you run it in the late
afternoon?  Wouldn't you want to see what you did in the morning and
early afternoon?

Because we cannot define "today" as "--since=today means the latest
midnight and later, while --until=today means until the end of today
[*]" without introducing an extra hint to calls to approxidate() to
tell it who is calling for what, it is impossible to give these two
sensible behavior at the same time.

    Side note: but because the existing history is all about the past,
    "until the end of today" is by definition a synonym for "up to
    now", so defining "today" the same as "now" would make "until"
    behave just as sensibly as if we define it as "the end of today".

In practice, using "--until" to *not* truncate at all (which is what
--until=now or --until=end.of.today would essentially mean) has no
practical value, while "--since=beginning.of.today" does have more
utility, allowing you to specify "the last 8 hours and 50 minutes"
without knowing that it is now at 08:50 in the morning.  So I am
still in favor of interpreting "today" as "the latest midnight, the
beginning of today" because that would give us a more useful
behavior than other possible definitions.  We may want to strengthen
the justification behind the chosen definition of why we chose what
we chose over any other time in today with something like what I
said above, mentioning "--until".

Thanks.