feat(client): map date-time-local and require an offset for zoned date-time - #135

@tanmaykm can we get a review of this PR to support undefined timezones? Currently only Julia OpenAPI generator forces an automatic use of UTC

Thanks for this, and for switching from :as_written to the registry format. Mapping date-time-local and requiring an offset for zoned date-time both look right per RFC 3339. Before merging, I'd like to settle a few things.

1. Avoid the contract bump for modules that don't use date-time-local

The client and server templates import _encode_zoned unconditionally, so every generated module becomes contract 5, including default datetime = :utc modules that never call it:

utc = OpenAPI.client(doc)          # no datetime option
occursin("_encode_zoned", utc)     # true
# emits Runtime.require_contract(5, ...)

A contract bump costs downstream users: a regenerated module can't load on older runtimes, so each consumer has to raise its OpenAPI compat bound and move its environments in step. For modules whose output is unchanged, that cost buys nothing. Could we keep them at contract 4? Two options:

• emit the _encode_zoned import and require_contract(5, …) only when the plan is :zoned and contains a date-time-local type; or
• emit the small _encode_zoned helper into the generated module itself under :zoned, so the runtime gains no new symbol and the contract stays at 4.

2. An offset on a wall-clock field is silently shifted, not rejected

date-time-local fields decode through _decode(::Type{Dates.DateTime}, …). That decoder accepts an optional offset and converts to UTC. Without a pattern on the schema:

# wall: {type: string, format: date-time-local}, datetime = :zoned
_decode(R, JSON.parse("""{"wall":"2026-08-07T15:00:00-04:00"}""")).wall
# 2026-08-07T19:00:00   (expected: DecodeError)

The test "an offset on a wall-clock field is rejected" passes only because its schema has a pattern forbidding offsets. A separate decode path for wall clocks under :zoned, one that rejects Z and offsets, would make the type itself enforce the format. Please also add a test that has no pattern.

3. Parameters and top-level bodies send a wall clock as UTC

The PR notes this as a limit, but the result is wrong bytes on the wire rather than an unsupported case. A date-time-local query, header or cookie parameter, or top-level body, encodes through _scalar/_encode and gets a Z:

OpenAPI.Runtime._scalar(DateTime(2026, 8, 7, 15))   # "2026-08-07T15:00:00.000Z"

The server then reads 15:00 local as 15:00 UTC. The maintainer guide asks generators to fail rather than approximate wire behavior. Please either route these paths through the wall-clock encoder, or have the planner reject date-time-local in those positions under :zoned until they're supported.

4. Release notes for the runtime change

The stricter ZonedDateTime decoder lives in OpenAPITimeZonesExt, so it applies to existing contract 3 and 4 :zoned modules as soon as an environment resolves the new release, without regeneration. I checked this against an existing contract-4 module: "2026-08-07T15:00:00" decodes on 1.2.0 and throws DecodeError on this branch. That's the intended fix, but it's a behavior change for deployed clients and servers, so the release notes should call it out explicitly. We should also decide whether it fits a minor release.

Minor: the \z anchor in the zoned decoder is a good catch. The same trailing-newline issue applies to the $ in _decode(::Type{Dates.DateTime}, …) in src/runtime.jl, so it might be worth fixing there too, here or in a follow-up.

tanmaykm Thanks for the careful review and the repros. I confirmed all five points. The next push has a change for each.

1. Contract. The runtime stays at contract 4. :zoned modules get _encode_zoned and _decode_zoned as module-local code. :utc modules generate the same output as on main.
2. Offsets on wall clocks. _decode_zoned rejects Z, offsets, and trailing newlines on date-time-local values, also in arrays and maps. The test schemas have no pattern.
3. Parameters and top-level bodies. Under :zoned, planning fails for date-time-local in a parameter, a header, or a whole body. This includes aliases. The docs state the rule.
4. Release notes. I reverted the change to OpenAPITimeZonesExt, so existing contract 3 and 4 modules keep their behavior. Only new :zoned modules require an offset. I think this fits a minor release.
5. \z. I fixed _decode(::Type{Dates.DateTime}, …) and added a test. This change reaches existing modules: a value with a trailing newline does not decode.

The same trailing-newline issue applies to schema pattern and patternProperties. #136 (QXT-Energy:jd/ecma-262-patterns) fixes it there: it compiles patterns with DOLLAR_ENDONLY, as ECMA-262 requires. The two PRs change different files and merge without conflict. The full test suite passes with both applied.

Suggested release notes for #135 and #136, as discussed in point 4:

• datetime = :zoned maps format: date-time-local to Dates.DateTime, a wall clock with no offset. Regenerate to use it.
• Newly generated :zoned modules reject a date-time value without Z or an offset, and a date-time-local value with one. Existing modules do not change.
• Under :zoned, planning rejects date-time-local in parameters, headers, and whole bodies.
• The runtime Dates.DateTime decoder rejects a value with a trailing newline. This applies to existing modules without regeneration.
• JSON Schema pattern and patternProperties follow ECMA-262 (fix(schema_engine): follow ECMA-262 semantics in pattern #136): $ does not match before a trailing newline, \d and \w are ASCII, \s and \S use the ECMA-262 white-space set, and . does not match a line terminator. This applies to existing modules without regeneration.

Thanks for the quick turnaround. I re-checked each point against ddd945b9:

1. Contract stays at 4, and :utc output is byte-identical to main. I checked the client and the server for a large real-world spec.
2. An offset on a date-time-local field is rejected with no pattern in the schema.
3. A date-time-local parameter fails planning with unsupported_date_time_local_position.
4. Existing contract-4 :zoned modules keep their behavior on this runtime. The suggested release notes look right.

Two non-blocking points:

Module-local codecs on every field. Under :zoned, every model field decodes through the module-local _decode_zoned, not just the date-time ones. For the spec above, that changes about 1,100 lines of :zoned output (548 call sites). It also means each generated module carries its own union decoder. That decoder ranks variants with an exact value isa V, while the runtime's _decode_union uses _direct_union_match (any non-Bool Integer, AbstractFloat, AbstractVector, and so on) and has the single-candidate fast path. It behaved the same in my tests, but it's a second copy that can drift. The planner knows each field's type at emission, so could _decode_zoned/_encode_zoned be used only where the type contains Dates.DateTime or TimeZones.ZonedDateTime? Other fields would stay on the runtime _decode/_encode. That would keep the diff for regenerated modules small and limit the copy to the date-time paths.

Fields vs. parameters. In a new :zoned module, a date-time field rejects a value without an offset, but a date-time query or header parameter still decodes it as UTC through the runtime. That seems acceptable, given the lenient runtime policy, but a sentence in clients.md stating it would help.

Neither point blocks merging; I'm happy to take them as follow-ups if you'd prefer.

Thanks for the quick turnaround. I re-checked each point against ddd945b9:

1. Contract stays at 4, and :utc output is byte-identical to main. I checked the client and the server for a large real-world spec.
2. An offset on a date-time-local field is rejected with no pattern in the schema.
3. A date-time-local parameter fails planning with unsupported_date_time_local_position.
4. Existing contract-4 :zoned modules keep their behavior on this runtime. The suggested release notes look right.

Two non-blocking points:

Module-local codecs on every field. Under :zoned, every model field decodes through the module-local _decode_zoned, not just the date-time ones. For the spec above, that changes about 1,100 lines of :zoned output (548 call sites). It also means each generated module carries its own union decoder. That decoder ranks variants with an exact value isa V, while the runtime's _decode_union uses _direct_union_match (any non-Bool Integer, AbstractFloat, AbstractVector, and so on) and has the single-candidate fast path. It behaved the same in my tests, but it's a second copy that can drift. The planner knows each field's type at emission, so could _decode_zoned/_encode_zoned be used only where the type contains Dates.DateTime or TimeZones.ZonedDateTime? Other fields would stay on the runtime _decode/_encode. That would keep the diff for regenerated modules small and limit the copy to the date-time paths.

Fields vs. parameters. In a new :zoned module, a date-time field rejects a value without an offset, but a date-time query or header parameter still decodes it as UTC through the runtime. That seems acceptable, given the lenient runtime policy, but a sentence in clients.md stating it would help.

Neither point blocks merging; I'm happy to take them as follow-ups if you'd prefer.

Yes, I can open new PRs as follow ups to these changes so we can get unblocked and contribute the rest