Re: git-2.13.0: log --date=format:%z not working

On Fri, May 26, 2017 at 8:33 PM, Ulrich Mueller [off-list ref] wrote:

The following commands work as expected (using commit b06d364310
in the git://git.kernel.org/pub/scm/git/git.git repo as test case):

$ export TZ=Europe/Berlin
$ git --no-pager log -1 --pretty="%ad" --date=iso b06d364310
2017-05-09 23:26:02 +0900
$ git --no-pager log -1 --pretty="%ad" --date=iso-local b06d364310
2017-05-09 16:26:02 +0200

However, if I use explicit format: then the output of the time zone is
wrong:

$ git --no-pager log -1 --pretty="%ad" --date="format:%F %T %z" b06d364310
2017-05-09 23:26:02 +0000
$ git --no-pager log -1 --pretty="%ad" --date="format-local:%F %T %z" b06d364310
2017-05-09 16:26:02 +0000

I would expect the output to be the same as in the first two examples.

This patch solves half of your problem, i.e. makes the latter
format-local case work:

diff --git a/date.c b/date.c
index 63fa99685e..469306ebf5 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_local_tm(timestamp_t time, int tz)
+{
+       time_t t = gm_time_t(time, tz);
+       return localtime(&t);
+}
+
 /*
  * What value of "tz" was in effect back then at "time" in the
  * local timezone?

@@ -214,10 +220,14 @@ const char *show_date(timestamp_t time, int tz,

const struct date_mode *mode)
                return timebuf.buf;
        }

-       tm = time_to_tm(time, tz);
-       if (!tm) {
-               tm = time_to_tm(0, 0);
-               tz = 0;
+       if (mode->type == DATE_STRFTIME) {
+               tm = time_to_local_tm(time, tz);
+       } else {
+               tm = time_to_tm(time, tz);
+               if (!tm) {
+                       tm = time_to_tm(0, 0);
+                       tz = 0;
+               }
         }

        strbuf_reset(&timebuf);

There's another test which breaks if we just s/gmtime/localtime/g. As
far as I can tell to make the non-local case work we'd need to do a
whole dance where we set the TZ variable to e.g. UTC$offset, then call
strftime(), then call it again. Maybe there's some way to just specify
the tz offset, but I didn't find any in a quick skimming of time.h.