how to get UTC timestamp for commit?

[Matt Mackall]

On Mon, 2015-08-17 at 10:18 +0200, Olaf Hering wrote:
> Assume this output:
> 
>  # mutt-hg $ hg log | head -n 4
>  # changeset:   6479:55ea6e829b46
>  # tag:         tip
>  # user:        Kevin McCarthy <kevin at 8t8.us>
>  # date:        Tue Aug 11 11:20:15 2015 -0700
> 
> I want to get the UTC date of this commit, like:
> 
>  # mutt-hg $ hg tip --template "{date(date, '%Y%m%dT%H%M%S')}.r{rev}\n"
>  # 20150811T112015.r6479
> 
> But it is reported as localtime.

It's not reported in localtime (your localtime is apparently +0200).
It's reported in the timezone of the committer (like email).

>  Looking through "hg help templates" I see a
> reference to "hg help dates":
> 
>         date(date[, fmt])
>                 Format a date. See "hg help dates" for formatting strings.
> 
> But that does not contain a list of formating strings as output, just various
> formats for input.

Right you are! This actually takes the standard % codes from
strftime(3) / date(1), but that won't help you because the timestamp
being formatted is in the wrong offset to start with.

> What is the format string to report UTC time? I do not have control over how
> hg(1) is invoked. All I can do is to pass options to --template.

Sadly, I don't think you can do it, then.

Mercurial dates are indeed stored in (UTC, offset) pairs, but the
templater always combines in the offset for display. There's a helper
function localdate which changes the offset to your current timezone, so
you can do {date|localdate|date}. If you then invoke hg with TZ=UTC,
you'll get a "local" time that's UTC. There is not at present a utcdate
helper.

-- 
Mathematics is the supreme nostalgia of our time.