COMPOSED_HANDLER mismatch when using different version of hono

[yusukebe]

What version of Hono are you using?

4.6.14

What runtime/platform is your app running on? (with version if possible)

any

What steps can reproduce the bug?

Sorry to reproduce and explain this problem is super difficult.

For example, this problem occurs when using the SSG helper. Suppose there are two projects in a monorepo: one called app, which defines the application, and one called ssg, which is used for SSG. If they are both using the same version of hono, there will be no problem. However, if they are using different versions, for example, app is using 4.6.13 and ssg is using 4.6.14, the SSG helper will not generate the files.

Repro: https://github.com/yusukebe/composed-handler-mismatch

This happens when onError is defined in subApp within the app application.

// projects/app/src/index.ts
import { Hono } from 'hono'

const subApp = new Hono()

subApp.get('/', (c) => c.html('Hi'))
subApp.onError((_e, c) => c.html('Error', 500))

const app = new Hono()
app.route('/', subApp)

export default app

This is because the handler to handle GET / request is marked as middleware not as a handler in the following code:

hono/src/helper/ssg/utils.ts

Lines 65 to 68 in 4eb101d

	const targetHandler = findTargetHandler(handler)
	if (['GET', METHOD_NAME_ALL].includes(method) && !isMiddleware(targetHandler)) {
	acc.push({ path })
	}

The reason is that the Symbol COMPOSED_HANDLER is recognized as a different key if the version is different in the following locations.

hono/src/utils/handler.ts

Lines 9 to 15 in 4eb101d

	export const findTargetHandler = (handler: Function): Function => {
	// eslint-disable-next-line @typescript-eslint/no-explicit-any
	return (handler as any)[COMPOSED_HANDLER]
	? // eslint-disable-next-line @typescript-eslint/no-explicit-any
	findTargetHandler((handler as any)[COMPOSED_HANDLER])
	: handler
	}

COMPOSED_HANDLER is defined in hono-base.ts.

hono/src/hono-base.ts

Line 34 in 4eb101d

export const COMPOSED_HANDLER = Symbol('composedHandler')

If you change the value of this COMPOSED_HANDLER to a string, this problem will be solved.

export const COMPOSED_HANDLER = '__COMPOSED_HANDLER'

Should it be a Symbol?

How about using a string like __COMPOSED_HANDLER instead of the Symbol? I think it is not a problem.

Is this a rare case?

Yes, it's a rare case. But this causes the issues: honojs/honox#234 honojs/honox#236 in HonoX. The issue is not caused by a difference in the version of hono, but it has deep nested dependencies. That will be resolved if making it string.

[yusukebe]

Hi @usualoma. What do you think of this?