fix(zod-validator): improve type inference for partial schemas

[dyyz1993]

Summary

Fixes Hono RPC type inference issue when using zValidator with partial schemas (e.g., schema.partial()).

Problem

When using zValidator('json', schema.partial()), the json field becomes optional in the middleware's Input type because HasUndefined<In> returns true when all fields are optional. This causes Hono RPC to not infer the json parameter for the client.

// Before: Client type inference fails
app.put('/:id', zValidator('json', schema.partial()), handler)
// Error: 'json' does not exist in type '{ param: { id: string } }'

Solution

Remove the HasUndefined check from DefaultInput type definition. This ensures:

• The json field itself is always required in the Input type
• The content within json can still be optional (e.g., { name?: string })
• Hono RPC can correctly infer the parameter type

type DefaultInput<Target extends keyof ValidationTargets, In, Out> = {
  in: { [K in Target]: [In] extends [ValidationTargets[K]] ? In : InferInput<In, K> };
  out: { [K in Target]: Out };
};

Test Plan

• Type checking passes
• Works with partial schemas
• Works with regular schemas
• Hono RPC client correctly infers json parameter

Breaking Changes

None. The validation behavior remains unchanged; only the type inference is improved.

[changeset-bot]

🦋 Changeset detected

Latest commit: be82f3b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@hono/zod-validator	Patch
@hono/zod-openapi	Patch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.68%. Comparing base (3b38070) to head (be82f3b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1724   +/-   ##
=======================================
  Coverage   92.68%   92.68%           
=======================================
  Files         112      112           
  Lines        3734     3734           
  Branches      946      946           
=======================================
  Hits         3461     3461           
  Misses        245      245           
  Partials       28       28           

Flag	Coverage Δ
zod-validator	91.30% <ø> (ø)

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