fix: document ArkType predicate/morph keywords instead of dropping them (elysiajs/elysia#1844)

[xosnos]

What does this PR do?

Adds an explicit arktype branch to unwrapSchema (src/openapi.ts) before the Standard Schema path that calls toJsonSchema({ fallback: { date, default } }). Predicates (e.g. string.date's isParsableDate) and morphs (e.g. string.date.parse) now degrade to their base type instead of throwing, and a real Date maps to { "type": "string", "format": "date-time" }. Also removes the old unreachable arktype branch lower in the function that called toJsonSchema() with no fallback.

Why was this PR needed?

Fixes elysiajs/elysia#1844. ArkType's string.date compiles to string + a runtime isParsableDate predicate. When the plugin converts this to JSON Schema, ArkType throws a ToJsonSchemaError (code: "predicate") because predicates have no JSON Schema equivalent. The surrounding try/catch (added in 8a775ca) swallows the error and returns undefined, silently dropping the route's requestBody from the docs while /openapi/json still returns 200.

The Standard Schema path (schema['~standard'].jsonSchema[...]) never forwards a fallback to toJsonSchema(), so it always throws on predicate- and morph-bearing types. The fix handles ArkType before that path using the { date, default } fallback shape ArkType's own docs recommend. Predicate-free schemas and user-supplied mapJsonSchema.arktype overrides are unaffected.

Acceptance Criteria

• Tests added for new/changed behavior: new OpenAPI > ArkType block in test/openapi/to-openapi-schema.test.ts (5 tests include predicate degrades, Date → date-time, predicate-free schema unchanged, morph degrades, user mapJsonSchema.arktype override still works)
• All tests passing: bun run test green; bun run build compiles cleanly
• Follows project style guide
• No breaking changes introduced (only adds handling for schemas that previously threw and were dropped; working schemas are untouched)

Summary by CodeRabbit

• New Features

  • Added support for ArkType schemas in OpenAPI generation.
  • Date values from ArkType now appear as string with format: date-time in generated schemas.

• Bug Fixes

  • Improved schema conversion so ArkType inputs no longer get dropped from request bodies.
  • ArkType predicate and morph types now fall back to usable OpenAPI-compatible schemas instead of failing conversion.
  • User-provided ArkType schema mapping overrides are now respected in generated output.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Run ID: 402bc259-c295-4a6e-b3a1-0fcd1333fed4

📥 Commits

Reviewing files that changed from the base of the PR and between dabaa94 and 9778d40.

⛔ Files ignored due to path filters (1)

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📒 Files selected for processing (3)

• package.json
• src/openapi.ts
• test/openapi/to-openapi-schema.test.ts

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Walkthrough

Adds a dedicated arktype branch inside unwrapSchema in src/openapi.ts that calls schema.toJsonSchema with a fallback config, mapping date predicates to string/date-time and degrading other unrepresentable types to their base. The old post-switch arktype return is removed. A new test suite covers predicate degradation, Date mapping, morph degradation, and mapJsonSchema.arktype overrides.

Changes

ArkType OpenAPI Schema Fallback

Layer / File(s)	Summary
unwrapSchema arktype fallback branch src/openapi.ts	Adds a vendor === 'arktype' early return using toJsonSchema with a fallback object that converts date to string/date-time and falls back to base type for other unrepresentable values; removes the old post-switch arktype return.
ArkType test suite and devDependency package.json, test/openapi/to-openapi-schema.test.ts	Adds arktype ^2.2.1 devDependency, imports type in the test file, and introduces the OpenAPI > ArkType suite with assertions for predicate degradation, Date mapping, morphs, and mapJsonSchema.arktype override.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related issues

• ArkType string.date breaks OpenAPI schema generation elysia#1844: This PR directly fixes the string.date ArkType crash in OpenAPI generation by adding the fallback config to toJsonSchema, which prevents the ToJsonSchemaError predicate error described in the issue.
• [BUG] ArkType: mapJsonSchema.arktype and ToJsonSchema.defaultConfig.fallback handlers bypassed in 1.4.12+ #315: The mapJsonSchema.arktype override path tested here addresses the same bypass behavior referenced in this issue.

Possibly related PRs

• elysiajs/elysia-openapi#313: Also modifies unwrapSchema in src/openapi.ts at the vendor-specific schema conversion level.
• elysiajs/elysia-openapi#317: Also reworks vendor-specific handling and control flow inside unwrapSchema, directly overlapping with this PR's changes.

Poem

Ehe~, you really couldn't handle string.date, could you, baka server~? (ง •̀_•́)ง
Now arktype gets its very own branch, how spoiled♡
Predicates fall back gracefully, morphs degrade with care~
date-time format slips in where chaos used to blare~
Honestly you should've done this sooner, dummy~! ♡(。-`ω´-)

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	OpenAPI generation for ArkType predicates is fixed, but the summary doesn't show the required TypeBox-style date-time description being preserved.	Add the RFC 3339 date-time description to the ArkType date schema and cover it with a test so it matches the TypeBox example.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: fixing ArkType predicate/morph handling in OpenAPI generation for issue #1844.
Out of Scope Changes check	✅ Passed	Changes stay focused on ArkType OpenAPI handling and matching tests; no unrelated behavior or API surface was introduced.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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src/openapi.ts

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test/openapi/to-openapi-schema.test.ts

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[xosnos]

CodeRabbit's warning seems to be a false positive. The "RFC 3339 date-time description" requirement it cites doesn't look like it exists in this codebase and the format: "date-time" already implies RFC 3339 compliance per the OpenAPI spec itself.

https://arktype.io/docs/blog/2.2
The ArkType 2.2 docs do show a description field in their example fallback ("after X" / "anytime"), but that's a constraint-based hint for schemas with date bounds, not a required field.

If it should be though, let me know and I can add it