std.date time problem

[Deewiant]

Regan Heath wrote:
> I think this is a bug, but I can't be sure.
> 
> [time.d]
> import std.stdio, std.date;
> 
> void main()
> {
>     d_time now = UTCtoLocalTime(getUTCtime());
>     writefln("%s", toTimeString(now));
> }
> 
> dmd -run time.d
> 10:54:42 GMT+0100
> 
> time /t
> 09:55
> 
> I am in London so at GMT, but it's summer so we're at +0100 currently
> (aka BST).  It seems std.date adds an extra hour?
> 

Yep, it's buggy. std.date does essentially the following in getLocalTZA() on
Windows (shortened to pseudocode):

TIME_ZONE_INFORMATION tzi;
GetTimeZoneInformation(&tzi);

if (unknown time zone || in standard time || in daylight savings time)
	return -(tzi.Bias + tzi.StandardBias) * 60 * TicksPerSecond;
else
	return 0; // error

Microsoft documents at http://msdn2.microsoft.com/en-us/library/ms725481.aspx that:

- "Bias" is "[t]he current bias for local time translation on this computer, in
minutes" and "UTC = local time + bias".

- "StandardBias" is "[t]he bias value to be used during local time translations
that occur during standard time."

- "DaylightBias" (not used in std.date) is "[t]he bias value to be used during
local time translations that occur during daylight saving time."

That is, UTC = local time + Bias + StandardBias, or UTC = local time + Bias +
DaylightBias, depending on whether DST is active or not.

However, Phobos uses StandardBias in all cases. It should use DaylightBias if
GetTimeZoneInformation returns TIME_ZONE_ID_DAYLIGHT.

In London, I presume that Bias is 0, StandardBias is 0, and DaylightBias is -60,
which is why std.date is wrong.

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