fix: infer type of undefinable parameters correctly #1397
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WalkthroughIntroduces IsSkipped type-based gating across context and schema merge utilities, adds new utility types (IsUnknown, IsUndefined, IsSkipped), updates merge logic to use IsSkipped, and adds a new type builder Undefinable to the type-system with a public alias t.Undefinable. Adds type-only tests verifying Undefinable inference. Changes
Estimated code review effort🎯 4 (Complex) | ⏱️ ~60 minutes Poem
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⚠️ Outside diff range comments (1)
src/types.ts (1)
667-667: Replace legacy undefined-check with IsSkipped for cookie mergeundefined extends A['cookie'] incorrectly treats unions like X | undefined as "skipped"; align with other fields by using IsSkipped.
Location: src/types.ts:667
- cookie: undefined extends A['cookie'] ? B['cookie'] : A['cookie'] + cookie: IsSkipped<A['cookie']> extends true ? B['cookie'] : A['cookie']
🧹 Nitpick comments (3)
test/types/index.ts (3)
2685-2689: Avoid runtime access of "~Routes"; use type-leveltypeofinsteadAccessing
app["~Routes"].post...is a value-level read and can throw if executed. Prefer the established pattern usingtypeofso this remains purely type-checked.- expectTypeOf(app["~Routes"].post.query).not.toEqualTypeOf<unknown>(); - expectTypeOf(app["~Routes"].post.query).toEqualTypeOf<{ name: string } | undefined>(); - expectTypeOf(app["~Routes"].post.headers).toEqualTypeOf<{ token: string } | undefined>(); - expectTypeOf(app["~Routes"].post.body).toEqualTypeOf<{ id: number } | undefined>(); + expectTypeOf<(typeof app)['~Routes']['post']['query']>().not.toBeUnknown() + expectTypeOf<(typeof app)['~Routes']['post']['query']>().toEqualTypeOf<{ name: string } | undefined>() + expectTypeOf<(typeof app)['~Routes']['post']['headers']>().toEqualTypeOf<{ token: string } | undefined>() + expectTypeOf<(typeof app)['~Routes']['post']['body']>().toEqualTypeOf<{ id: number } | undefined>()
2685-2689: Optional: assert headers/body are notunknownfor completenessMirror the query assertion to ensure headers/body don’t regress to
unknown.+ expectTypeOf<(typeof app)['~Routes']['post']['headers']>().not.toBeUnknown() + expectTypeOf<(typeof app)['~Routes']['post']['body']>().not.toBeUnknown()
2677-2683: Stylistic nits: align quotes/semicolons with file conventionsMost of this file uses single quotes and omits trailing semicolons. Consider matching that for consistency.
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📒 Files selected for processing (4)
src/context.ts(3 hunks)src/type-system/index.ts(2 hunks)src/types.ts(4 hunks)test/types/index.ts(1 hunks)
🧰 Additional context used
🧬 Code graph analysis (1)
src/context.ts (1)
src/types.ts (2)
IsSkipped(753-753)ResolvePath(239-249)
🔇 Additional comments (9)
src/type-system/index.ts (2)
583-583: Public alias looks good.Exposing as
t.Undefinablekeeps parity with existing helpers.
422-427: Clarify Undefinable semantics & verify OpenAPI/JSON Schema handling of TypeBox UndefinedFile: src/type-system/index.ts (lines ~422-427)
- Update the doc comment: this builder unions with Undefined only and does NOT mark properties optional. Suggested diff:
/** - * Allow Optional and Undefined + * Allow Undefined (does NOT mark properties optional) */ Undefinable: <T extends TSchema>(schema: T, options?: SchemaOptions) => t.Union([schema, t.Undefined()], options),
- Verify your schema→OpenAPI/JSON Schema emitter tolerates TypeBox's Undefined inside unions (or document/transform it). If no emitter exists in this repo, state where conversion happens so compatibility can be checked.
src/types.ts (4)
657-660: Move to IsSkipped for body/headers/query merge — good.This fixes the “undefined extends T” pitfall and preserves unions like
T | undefined.
682-703: Standalone merge for body/headers/query updated correctly.Symmetric
IsSkippedbranching reads well.
710-717: Cookie standalone merge aligned — good.This further highlights the inconsistency in MergeSchema’s cookie; fix there as noted.
745-754: Helper types look correct and non-distributive.
IsUnknownexcludesanyand matches only exactunknown.IsUndefinedchecks exactundefinedvia tuple wrapping.IsSkippedcomposition is clear.src/context.ts (3)
15-17: Importing IsSkipped for gating — good.Keeps types local and avoids repeating logic here.
33-51: ErrorContext gating now respects unknown/exact-undefined — good.Safer defaults for query/headers/cookie while preserving typed branches when provided.
126-146: Context query/params/headers/cookie gating updated correctly.Behavior now matches the new inference strategy; params fallback handling still covers path-derived types.
Addresses #1395
The main cause of the problem is,
undefined extends Tis true forT = undefined | Somethingso any type that had that signature was being resolved to the default type.I added proper
IsUndefinedcheck. Also noticed that it should also fallback to the default type when the type is unknown, so I addedIsUnknowncheck. Then, I merged them in theIsSkippedcheck so that can be used generally for these cases. If the condition to fallback to the default type changes in the future, it will be enough to change the implementation ofIsSkipped.Finally, added a
t.Undefinablehelper.t.Optionalwould have been a better name but Typebox uses it for making a schema partial.t.MaybeEmptyalso includesnulltype, and that makes this syntax not possible:I know the changes I made are somewhat risky and intrusive. And I know you are working on integrating standard-schema. So feel free to modify or discard this PR. But I think a change like this is needed, as there is no way to have a type that is unioned with undefined at the moment.
Note: A similar change is also needed for Eden, and I am planning to also make that if this is merged. Because the same problem exists there too.
Summary by CodeRabbit
New Features
Improvements
Tests