[PATCH 2/2] date: use localtime() for "-local" time formats
- From
Jeff King <peff@peff.net>
- Date
- Jun 15, 2017, 13:52 UTC
- Message-ID
- <20170615135216.2jfsrjpicku6zxv3@sigill.intra.peff.net>
- In-Reply-To
- <20170615134958.mzmdmhonjsnconu2@sigill.intra.peff.net>
When we convert seconds-since-epochs timestamps into a broken-down "struct tm", we do so by adjusting the timestamp according to the known offset and then using gmtime() to break down the result. This means that the resulting struct "knows" that it's in GMT, even though the time it represents is adjusted for a different zone. The fields where it stores this data are not portably accessible, so we have no way to override them to tell them the real zone info.
For the most part, this works. Our date-formatting routines don't pay attention to these inaccessible fields, and use the same tz info we provided for adjustment. The one exception is when we call strftime(), whose %Z format reveals this hidden timezone data.
We solved that by always showing the empty string for %Z. This is allowed by POSIX, but not very helpful to the user. We can't make this work in the general case, as there's no portable function for setting an arbitrary timezone (and anyway, we don't have the zone name for the author zones, only their offsets).
But for the special case of the "-local" formats, we can just skip the adjustment and use localtime() instead of gmtime(). This makes --date=format-local:%Z work correctly, showing the local timezone instead of an empty string.
The new test checks the result for "UTC", our default test-lib value for $TZ. Using something like EST5 might be more interesting, but the actual zone string is system-dependent (for instance, on my system it expands to just EST). Hopefully "UTC" is vanilla enough that every system treats it the same.
Signed-off-by: Jeff King <peff@peff.net> --- I don't have a Windows system to test this on, but from the output Dscho provided earlier, I believe this should pass.
date.c | 14 ++++++++++++-- t/t0006-date.sh | 1 + 2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/date.c b/date.c index 558057733..1fd6d6637 100644 --- a/date.c +++ b/date.c @@ -70,6 +70,12 @@ static struct tm *time_to_tm(timestamp_t time, int tz) return gmtime(&t); } +static struct tm *time_to_tm_local(timestamp_t time) +{ + time_t t = time; + return localtime(&t); +} + /* * What value of "tz" was in effect back then at "time" in the * local timezone? @@ -214,7 +220,10 @@ const char *show_date(timestamp_t time, int tz, const struct date_mode *mode) return timebuf.buf; } - tm = time_to_tm(time, tz); + if (mode->local) + tm = time_to_tm_local(time); + else + tm = time_to_tm(time, tz); if (!tm) { tm = time_to_tm(0, 0); tz = 0; @@ -246,7 +255,8 @@ const char *show_date(timestamp_t time, int tz, const struct date_mode *mode) month_names[tm->tm_mon], tm->tm_year + 1900, tm->tm_hour, tm->tm_min, tm->tm_sec, tz); else if (mode->type == DATE_STRFTIME) - strbuf_addftime(&timebuf, mode->strftime_fmt, tm, tz, ""); + strbuf_addftime(&timebuf, mode->strftime_fmt, tm, tz, + mode->local ? NULL : ""); else strbuf_addf(&timebuf, "%.3s %.3s %d %02d:%02d:%02d %d%c%+05d", weekday_names[tm->tm_wday], diff --git a/t/t0006-date.sh b/t/t0006-date.sh index 9f81bec7a..7ac9466d5 100755 --- a/t/t0006-date.sh +++ b/t/t0006-date.sh @@ -56,6 +56,7 @@ check_show unix-local "$TIME" '1466000000' check_show 'format:%z' "$TIME" '+0200' check_show 'format-local:%z' "$TIME" '+0000' check_show 'format:%Z' "$TIME" '' +check_show 'format-local:%Z' "$TIME" 'UTC' check_show 'format:%%z' "$TIME" '%z' check_show 'format-local:%%z' "$TIME" '%z'
-- 2.13.1.766.g6bea926c5