Dates before the year 1901 are not handled correctly by `canonicalDate` and `exactDate`

[tdammers]

The Year type faithfully represents all the years from -271820 to 275759, but passing, e.g., toEnum 1 into canonicalDate produces a date in the year 1901, not the year 1 as one would expect.

Example code:

show <<< year $ canonicalDate (fromMaybe bottom $ toEnum 1) January bottom

...produces "(Year 1901)", instead of "(Year 1)".

The culprit seems to be on the JavaScript side of things; while the Date type can represent dates like '0001-01-01', creating them the way canonicalDate does, which is new Date(Date.UTC(y, m - 1, d)), "helpfully" "fixes" the year number to after 1900.

[garyb]

Ughh thanks, yeah I guess we'll have to massage the input values some if we want to keep using the JS stuff to do the date logic. Well, we don't really, but I also don't trust myself to implement it correctly in PS either 😕

[tdammers]

Figured this much.

In case it helps, some quick toying with JS's Date ctor reveals that you can construct the desired dates if you pass in a string, like so:

> new Date('0001-01-01')
0001-01-01T00:00:00.000Z

...but getting the format wrong breaks things rather badly:

> new Date('0001-1-1')
2000-12-31T23:00:00.000Z

[anilanar]

I think this can be solved without reinventing the wheel of DateTime. I'll give it a try.