Create an Ideal Components Bag / Skeleton for DateTimeFormat

[gregtatum]

This is a meta issue to track implementing the "ideal components bag" as laid out in the DateTimeFormat Deep Dive 2021-10-01 design document. Originally there was some discussion to have this replace the current components bag, but it is to be implemented alongside the existing components bag. A better name can be bikeshed if needed.

The following need to be completed.

• Prototype an initial data provider for the Ideal Components Bag #1318
• Create an initial implementation of the Ideal Components Bag in the experimental directory. #1319
• Upstream CLDR changes for the Ideal Components Bag #1321
• Write/complete documentation for the Ideal Components Bag  #1325
• Create benchmarks for the ideal Components Bag #1322
• Compare the quality of the Ideal Components Bag with ICU4C and existing components bag implementation #1323
• Promote the Ideal Components Bag out of experimental #1324

[sffc]

@gregtatum will provide mentorship.

[zbraniecki]

I'm spreading the word about this issue looking for candidates.

More details:

Description: Currently, DateTimeFormat has two ways to select the right format, both of them are imperfect. We believe we have a balanced novel solution that, once implemented, will become the foundational use of the DateTimeFormat.
Scope: We believe that the initial implementation should take one person several (2-3) months to implement. Hopefully in time for ICU4X 1.0.
Mentorship: This project is well staffed on the mentorship side with @gregtatum from Mozilla, @sffc from Google and @zbraniecki from Amazon willing to invest time to mentor the engineer who'll pick it.
How to start: If you are interested in the project, comment in this issue or join unicode-org.slack.com #icu4x and we'll get you on-ramped.

[ozghimire]

I'm interested to work on this issue.

[zbraniecki]

@gregtatum are you still open to mentor?

[pdogr]

If this issue is still open, I'm definitely interested to work on this.

[gregtatum]

@ozghimire Great! How would you prefer to get started? There is a document linked above outlining the strategy which should discuss how to get things going. I would suggest starting with #1318. I will fill in more details on that issue.

@pdogr I think ozghimire is taking the first step on this to move it forward, and it's hard to parallelize this initial step, but there will probably be work to help out on around the issues. You could take another DateTimeFormat issue to get onboarded. I'm sure there will be opportunities to help in the short term. #1581 would be a good bug to onboard with if you wanted to take it.

[randomicon00]

Hello @gregtatum, are still looking for contributors?

[sffc]

Working on the combined date/time pattern overrides.

All classical skeleta across all locales and calendars in CLDR (as a comma-separated list):

Bh,Bhm,Bhms,d,E,EBhm,EBhms,Ed,Ehm,Ehm-alt-ascii,EHm,Ehms,Ehms-alt-ascii,EHms,Gy,GyMd,GyMMM,GyMMMd,GyMMMEd,h,h-alt-ascii,H,hm,hm-alt-ascii,Hm,hms,hms-alt-ascii,Hms,hmsv,hmsv-alt-ascii,Hmsv,hmv,hmv-alt-ascii,Hmv,M,Md,MEd,MMM,MMMd,MMMEd,MMMMd,MMMMW-count-one,MMMMW-count-other,ms,y,yM,yMd,yMEd,yMMM,yMMMd,yMMMEd,yMMMM,yQQQ,yQQQQ,yw-count-one,yw-count-other,MMMMEd,MMdd,MMMMW-count-zero,MMMMW-count-two,MMMMW-count-few,MMMMW-count-many,yMM,yw-count-zero,yw-count-two,yw-count-few,yw-count-many,GyMMMM,GyMMMMd,GyMMMMEd,MMMM,MMMMdd,yMMMMd,yMMMMEd,MMd,hmsvvvv,Hmsvvvv,hmvvvv,Hmvvvv,yQ,yMMdd,GyMMMEEEEd,MMMEEEEd,MMMMEEEEd,yMMMEEEEd,yMMMMEEEEd,Md-alt-variant,MEd-alt-variant,MMdd-alt-variant,yMd-alt-variant,yMEd-alt-variant,MMMdd,mmss,HHmmZ,yMMMMccccd,EEEEd,MEEEEd,yMEEEEd,HHmmss,Mdd,Hmm,HHmm,GyM,yyyy,yyyyM,yyyyMd,yyyyMEd,yyyyMMM,yyyyMMMd,yyyyMMMEd,yyyyMMMM,yyyyQQQ,yyyyQQQQ,yyyyMMMMd,yyyyMMMMEd,yyyyMM,yyyyMMMEEEEd,yyyyMMMMEEEEd,yyyyMd-alt-variant,yyyyMEd-alt-variant,yyyyMMMMccccd,yyyyMMdd,yyyyMEEEEd,GyMEEEEd,UM,UMd,UMMM,UMMMd,UMd-alt-variant,HmZ

Of those, the ones that span date/time/zone are:

EBhm
EBhms
Ehm
EHm
Ehms
EHms
hmsv
Hmsv
hmv
Hmv
hmsvvvv
Hmsvvvv
hmvvvv
Hmvvvv
HHmmZ
HmZ

In order to keep a fixed set of auxiliary keys known at compile time, I will proceed to hard-code and generate those sets. I will store them only when they differ from the glue-based pattern. I will also open an issue to add a test that will inform us if any more such skeleta get added in the future.