Bcl provider returns non-bcl zones

[GoogleCodeExporter]

I would expect something like this to work:

    var bcl = DateTimeZoneProviders.Bcl;
    var zones = bcl.Ids.Select(id => bcl[id])
                       .Cast<BclDateTimeZone>()
                       .Select(x => new {x.Id, x.DisplayName})
                       .ToList();

But it fails since the Bcl provider returns a few zones that are 
FixedDateTimeZone instead of BclDateTimeZone.   Specifically, they are "UTC", 
"UTC+12", "UTC-02", and "UTC-11".

While I understand that these zones *can* be represented as a fixed offset, 
shouldn't they still be delivered as a BclDateTimeZone since I used the Bcl 
provider?

Casting to a BclDateTimeZone is the only way to get at DisplayName, which is 
how I found this.  Other than calling TimeZoneInfo.FindSystemTimeZoneById, I 
can't think of another way to get back a display name such as "(UTC) 
Coordinated Universal Time" without hardcoding it.

Original issue reported on code.google.com by mj1856 on 26 Sep 2014 at 8:58

[GoogleCodeExporter]

Hmm. The issue is DateTimeZoneCache, which checks whether the ID corresponds to 
a FixedDateTimeZone before it checks the provider. This corresponds with the 
behaviour documented in IDateTimeZoneProvider. (You can ask the provider for 
any fixed-offset zone, whether or not it's in Ids.)

We should probably think about this carefully at the same time as issue 282.

I wish this were a simple implementation issue :(

Original comment by jonathan.skeet on 26 Sep 2014 at 9:15

[GoogleCodeExporter]

Original comment by malcolm.rowe on 19 Feb 2015 at 1:14

• Added labels: Milestone-2.0-consider

[malcolmr]

If we're doing this at all, it'll have to be for 2.0.0.

[jskeet]

Note: we probably need to check anything else that uses DateTimeZone.ForOffset and providers, to make sure the precedence is okay.

[jskeet]

In particular: https://github.com/nodatime/nodatime/blob/master/src/NodaTime/Text/ZonedDateTimePatternParser.cs#L157