feat(zod-openapi): infer env from routeMiddleware

[oberbeck]

This PR is my initial proposal for adding type inference support for the zod-openapi middleware package, improving type safety when using middleware within the router definition.

Example usecase:

middleware/packages/zod-openapi/test/index.test-d.ts

Lines 268 to 304 in aca9bfd

	const app = new OpenAPIHono<{Variables: { too: Symbol }}>()
	app.openapi(
	createRoute({
	method: 'get',
	path: '/books',
	middleware: [
	createMiddleware<{
	Variables: { foo: string }
	}>((c, next) => {
	c.set('foo', 'abc')
	return next()
	}),
	createMiddleware<{
	Variables: { bar: number }
	}>((c, next) => {
	c.set('bar', 321)
	return next()
	}),
	] as const,
	responses: {
	200: {
	description: 'response',
	},
	},
	}),
	(c) => {
	c.var.foo
	c.var.bar
	c.var.too
	type verifyFoo = Expect<Equal<typeof c.var.foo, string>>
	type verifyBar = Expect<Equal<typeof c.var.bar, number>>
	type verifyToo = Expect<Equal<typeof c.var.too, Symbol>>
	return c.json({})
	}
	)

Background

I'm fairly new to HonoJS, but I've been very excited to explore its potential, especially the zod-openapi integration. However, I noticed that middleware types seem to be dropped when used alongside the OpenAPI package, which can impact type consistency and developer experience.

Potentially resolving:

• [zod-openapi] Route with middleware doesn't infer context variables #715
• [zod-openapi] The recommended way to apply middleware loses Context type info #637
• ...

Potential alternative

• [zod-openapi] Route with middleware doesn't infer context variables #715 (comment)

Thank you for considering this suggestion! Please feel free to suggest improvements or adjustments to align it with the project's requirements.

[changeset-bot]

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