There are a few FIXMEs that will need to be addressed, but this
implements most of the prototype method. The FIXMEs are mostly related
to range formatting, which has been entirely ignored so far. But other
than that, the following will need to be addressed:
* Determining flexible day periods must be made locale-aware.
* DST will need to be determined and acted upon.
* Time zones other than UTC and calendars other than Gregorian are
ignored.
* Some of our results differ from other engines as they have some
format patterns we do not. For example, they seem to have a lonely
{dayPeriod} pattern, whereas our closest pattern is
"{hour} {dayPeriod}".
Unlike the locale, the data locale has Unicode locale extensions removed
(e.g. the data locale for "en-US-u-ca-gregory" is just "en-US"). Cache
the data locale for LibUnicode lookups during formatting.
This was an oversight in e42d954743.
These fields should always follow the locale preference in the CLDR.
Overriding these fields would permit formats like "h:mm:ss" to result in
strings like "1:2:3" instead of "1:02:03".
TR-35's Matching Skeleton algorithm dictates how user requests including
fractional second digits should be handled when the CLDR format pattern
does not include that field. When the format pattern contains {second},
but does not contain {fractionalSecondDigits}, generate a second pattern
which appends "{decimal}{fractionalSecondDigits}" to the {second} field.
ECMA-402 doesn't explicitly handle a note in the TR-35 spec related to
expanding field lengths based on user-provided options. Instead, it
assumes the "implementation defined" locale data includes the possible
values.
LibUnicode does not generate every possible combination of field lengths
in its implementation of TR-35's "Missing Skeleton Fields", because the
number of generated patterns would grow out of control. Instead, it's
much simpler to handle this difference at runtime.
Other implementations unconditionally initialize [[pattern12]] from
[[pattern]] regardless of whether [[pattern]] has an hour pattern of h11
or h12. LibUnicode does not do this. So when InitializeDateTimeFormat
defaults the hour cycle to the locale's preferred hour cycle, if the
best format didn't have an equivalent hour pattern, [[pattern12]] will
be empty.
This is not a calendar supported by ECMA-402, so let's not waste space
with its data.
Further, don't generate "gregorian" as a valid Unicode locale extension
keyword. It's an invalid type identifier, thus cannot be used in locales
such as "en-u-ca-gregorian".
This allows us to only perform checks like export bindings existing only
for modules. Also this makes it easier to set strict and other state
variables with TemporaryChanges.
In static init blocks 'await' cannot be used. Note that this does not
cover all the cases since the parser currently cannot distinguish
between expressions within parenthesis and direct expressions.
This makes it a lot easier to understand what is going wrong when an
eval test fails. As an example instead of just getting:
`ExpectationError`
You would now get:
`ExpectationError: Expected _1_2E+0_1_ to eval to _12_ but got _120_`.
