Type-Safe Client fails to infer json field when combining path parameters with zValidator

[nekoze1210]

Based on the conversation history, you're asking me to write a GitHub issue about a Type-Safe Client bug where path parameters combined with zValidator for JSON validation cause type inference problems. Here's the issue:

Type-Safe Client fails to infer json field when combining path parameters with zValidator

What version of Hono are you using?

Latest (based on current main branch)

What runtime/platform is your app running on?

All runtimes (TypeScript type inference issue)

What steps can reproduce the bug?

1. Create a Hono route with path parameters and zValidator for JSON validation:

import { z } from 'zod'
import { zValidator } from '@hono/zod-validator'

const endJournalSessionSchema = z.object({
  summary: z.string().optional(),
});

const app = new Hono()
  .put(
    "/:id/end",
    zValidator("json", endJournalSessionSchema),
    (c) => c.json({ success: true })
  )

2. Try to use the Type-Safe Client:

import { hc } from 'hono/client'

type AppType = typeof app
const client = hc<AppType>('http://localhost')

// This fails with type error
const res = await client[":id"].end.$put({
  param: { id: "123" },
  json: { summary: "test" }  // Type error: 'json' does not exist
})

What is the expected behavior?

The Type-Safe Client should infer that both param and json fields are required in the request arguments, similar to how it works when multiple validators are used without path parameters.

What do you see instead?

TypeScript error:

Object literal may only specify known properties, and 'json' does not exist in type '{ param: { id: string; }; }'

The client type inference only recognizes the param field and completely ignores the json validator.

Additional information

• This issue occurs specifically when combining path parameters (:id) with zValidator for JSON validation
• The issue does NOT occur when using multiple validators without path parameters 1
• Server-side validation works correctly - the issue is purely with client-side type inference
• Adding an explicit validator('param', ...) does not resolve the issue
• Workaround: Using type assertion as any allows the code to work at runtime

The root cause appears to be in the Type-Safe Client's type inference system 2 where the schema-to-input type mapping doesn't properly merge path parameters with other validation targets when using zValidator.

This affects the developer experience significantly as it breaks type safety for a common pattern of having authenticated endpoints with path parameters that also accept JSON payloads.