Add Sedate IXDTF (extended ISO) string parsing function

[sffc]

We should add a function that parses ISO-8601 strings. We should follow the Temporal grammar:

https://tc39.es/proposal-temporal/#sec-temporal-iso8601grammar

i.e., we should implement a string parser conforming to IETF Sedate that parses a string into its components (date, time, time zone, calendar), and use this parser in APIs and anywhere else we parse date strings. Think about where to put this code in the crate structure.

We should start with the DateTime production, and work our way up towards CalendarDateTime and TemporalZonedDateTimeString.

Examples of strings that are accepted as part of the DateTime grammar:

• 2022-06-27T16:31:00.000
• 2022-06-27t16:31:00.000
• 2022-06-27 16:31:00.000
• 20220627 16:31:00.000
• 20220627 163100.000
• 20220627 163100
• 20220627 1631

[sffc]

Note: currently we have https://unicode-org.github.io/icu4x-docs/doc/icu_datetime/mock/fn.parse_gregorian_from_str.html

We should start with a design doc for this. We likely want to end up with a parser type named something like IetfDateTimeStringParser that is able to support the whole grammar.

[sffc]

Question: do we want to have specific, stricter parsers for each individual type, as well as the fully-featured one conforming to IETF Sedate?

[sffc]

We need to design how the parser will be architected so that it can be easily implemented.

Discuss with:

• @zbraniecki
• @skius
• @sffc
• @younies
• @Manishearth

Optional:

• @robertbastian

[robertbastian]

Do we want to leverage an existing implementation, such as the time crate?

[nekevss]

Hi! FWIW, we have an initial parsing implementation in temporal_rs. Although, it admittedly needs more testing and clean up.

[Manishearth]

Do we want to leverage an existing implementation, such as the time crate?

Open to doing so with a Cargo feature.

Though I think this is the kind of thing that is okay for us to expose if we wish.

[sffc]

I think a SEDATE parser should be its own crate. Maybe it lives in our repo, maybe in the temporal_rs repo, maybe but maybe not in the time or chrono repo.

[sffc]

I changed the title of this issue to emphasize that we're talking about IXDTF, which is not functionality I'm aware of in Rust except for temporal_rs mentioned above.

[nekevss]

Just to expand on my above comment. From what I can tell after reading through the IETF doc, I think the parser in temporal_rs can parse Sedate IXDTF or, at least, is fairly close to it. There might be a couple things missing, and the API definitely needs some work if the decision were to use that parser.

I'm pretty neutral on whether the functionality lives in icu4x, temporal_rs, or its own crate. I mostly figured that I would mention that it exists if there was interest in using the currently existing one as a base or just cleaning it up and using what's there. 😄

For reference, here are all the tests for that parser.

[sffc]

Thanks for the reference! Looking over that code, it seems to be well-written and suitable as a dependency of the icu4x project. I think it would be worthwhile pulling this code into an ixdtf crate (it looks like we are currently squatting that crate name). Seems harmless to include the Duration parsing code as well. The parser should return the raw IsoParseRecord type so that it isn't specific to the types in either icu_calendar or temporal_rs.

[nekevss]

Sounds good. I'll move the code over to the directory. update it with the above comments., and submit a PR

[sffc]

Discussion: after @nekevss's PR is landed, we will add ixdtf as an optional, default dependency of icu_calendar and use where necessary.

LGTM: @sffc @Manishearth @robertbastian

[sffc]

4646 basically fixes this issue but there were some minor follow-ups. I'm re-opening this issue to track that, or we can move those to another issue and re-close this one.

[nekevss]

I can definitely work on the follow ups for the ixdtf as needed. I think it makes sense to have a separate issue to track progress on any follow ups needed on ixdtf.

[sffc]

Schedule release review for the IXDTF crate

Start: 11:01

Options:

1. Ship as 0.x when @sffc and @nekevss feel it is ready
2. Ship as 0.x after an API review with the team
3. Ship as 1.0 after an API review with the team

Discussion:

• @nekevss - A 1.0 release would make sense if we can point to RFC 9557. It is soon to be published but it's not published yet.
• @sffc - It sounds like we could start with 1 or 2 and be prepared to ship 1.0 when RFC 9557 is out.
• @robertbastian - I'm happy with any conclusion of the domain experts (@sffc and @nekevss) because it doesn't put requirements on the ICU4X project itself

[sffc]

Checklist:

• [ ] The crate should fully conform with the ICU4X Style Guide:
  • [ ] The crate should have a complete library header as shown in boilerplate.md with Clippy passing
  • [ ] The names of exported types should conform to the recommendations in the Style Guide
  • [ ] All Error types should be Copy
  • [ ] All constructors should take options structs by value
  • [ ] All constructors should take arguments in the following order: Provider, Locale, Options
  • [ ] All constructors should have the standard set of overloads for provider types
  • [ ] Runtime dependencies should be minimal and able to be disabled with Cargo features if possible
  • [ ] Any TODO, FIXME, todo!, unimplemented!, or other placeholders should either be resolved or link to an issue number. (It is okay to ship a small amount of code with tech debt comments, but anything having to do with code correctness should be resolved)
• [ ] The crate should have a conventional Cargo.toml file:
  • [ ] Cargo.toml should use license, not license-file
  • [ ] The description should be useful
  • [ ] Correct repo link, authors, categories, include
  • [ ] Correct docs.rs and cargo-all-features metadata settings
  • [ ] A rust-version field with the MSRV of this crate in accordance with the current ICU4X policies on MSRV.
  • [ ] The crate should have an std feature if (and only if) it contains code that depends on std, such as file I/O or implementing the Error trait
  • [ ] Audit all features so that any foo/bar in a feature is foo?/bar when foo is an optional dep; if you intend to enable foo, add two entries
  • [ ] Use dep: for enabling dependencies
• [ ] The crate should be fully documented
  • [ ] Every exported function should have docs coverage
  • [ ] There should be a crate-level example that illustrates a common use case for the component with the heading # Examples
  • [ ] All options and conditional code paths should have a corresponding docs test with the heading # Examples
  • [ ] All functions that are conditional on a Cargo feature should say so (last line before # Examples): ✨ *Enabled with the `alloc` Cargo feature.*
  • [ ] Compiled data constructors should say "with compiled data" in the first sentence and should have a Cargo feature alert following the above syntax.
• [ ] The APIs should follow ICU4X style
  • [ ] All options bags should be Copy (and contain references if they need to). Exceptions can be made by discussion.
• [ ] The data structs should fully follow ZeroVec style
  • [ ] Deserialization should not have a "zero-copy violation" in the make-testdata test
  • [ ] Constructors should avoid allocating memory in the common case
  • [ ] Opaque blobs of data should be avoided if possible (instead use VarZeroVec, ZeroMap, etc.)
  • [ ] Data structs should not be panicky to load/deserialize and conform to data_safety.md
• [ ] The component should be fully integrated with ICU4X tooling
  • [ ] There should be an overview Criterion benchmark
  • [ ] There should be individual Criterion benchmarks for interesting or performance critical code paths
  • [ ] There should be at least one example plumbed with the icu_benchmark_macros
  • [ ] The component should be fully covered by FFI with no unjustified suppressions nor entries in missing_apis.txt
• [ ] The component should encourage i18n best practices
  • [ ] The component should produce correct results in all locales as generated by icu4x-datagen
  • [ ] Where applicable, the component should be consistent with ECMA-402 and UTS#35
  • [ ] Any gaps in i18n quality should be fixed, or, if that is not possible, they should have tracking issues and a concrete, resourced path forward. The intent is to not ship components with known i18n correctness problems and no plan to fix them in an upcoming release
  • [ ] The API design should receive sign-off from a non-ICU4X i18n expert such as Markus Scherer
• [ ] Add the new features to the changelog in the "Unreleased" section

[sffc]

• @nekevss - Should we release the 1.0 when the RFC is out?
• @sffc - I think we said yes; maybe we could incubate at a pre-1.0 for a release? It seems rushed if we do the 1.0 release so soon after the implementation landed, even if the RFC is done.
• @sffc - How about this. Once temporal_rs and icu_calendar are both using IXDTF, we can consider that sufficient experience to be able to make a 1.0 release of ixdtf.

Plan:

1a. @sffc to finish the IXDTF checklist. 1b. @sffc to add ixdtf as a depedency of the icu_calendar crate and use it 1c. @nekevss to bring the docs up to par with the checklist requirements

2. Release ixdtf at 0.x
3. Add ixdtf as a depedency of the temporal_rs crate and use it
4. We consider icu_calendar and temporal_rs experience to be sufficient for making a 1.0 release of ixdtf