feat(mount): introduce Mount Middleware and deprecate app.mount

[yusukebe]

I realized that app.mount() doesn't need to be placed in hono-base.ts. The codebase of app.mount() is a little bit fat compared to other methods in hono-base.ts, though the lines are very few in the real world. Anyway, the unnecessary should be removed from hono-base.ts.

So, we can make it a middleware called Mount Middleware. The usage is below:

import { Router as IttyRouter } from 'itty-router'
import { Hono } from 'hono'
import { mount } from 'hono/mount'

const ittyRouter = IttyRouter()
ittyRouter.get('/hello', () => new Response('Hello from itty-router'))

const app = new Hono()
app.all('/itty-router/*', mount(ittyRouter.handle))

I think the API syntax is very Hono-like and love it.

As a result, the bundle size will be 501B smaller (vs current main):

This PR will obsolete app.mount() completely, so this is a breaking change. Should be introduced in the next major release v5.

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.30%. Comparing base (6abd35b) to head (23f2249).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5221      +/-   ##
==========================================
+ Coverage   80.24%   80.30%   +0.06%     
==========================================
  Files         148      149       +1     
  Lines       10472    10504      +32     
  Branches     2336     2347      +11     
==========================================
+ Hits         8403     8435      +32     
  Misses       2069     2069              

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[yusukebe]

Hey @usualoma !

What do you think of moving the mount feature from hono-base.ts to middleware? I want your opinion on the direction only (no implementation yet)!

[usualoma]

@yusukebe
That's a great change!

I think mount is a feature that symbolizes Hono, but I don't think it's a “characteristic of the Hono instance itself,” so I think it makes sense for it to be implemented as middleware (which will also make the Hono instance smaller).

[github-actions]

Bundle size check

	main (95eb860)	#5221 (156878b)	+/-
Bundle Size (B)	18,335B	18,335B	0B
Bundle Size (KB)	17.91K	17.91K	0K

Compiler Diagnostics (tsc)

	main (95eb860)	#5221 (156878b)	+/-
Files	83	83	0
Lines	59,444	59,446	+2
Identifiers	60,624	60,625	+1
Symbols	106,532	106,532	0
Types	163,092	163,092	0
Instantiations	414,023	414,023	0
Memory used	205,718K	209,114K	+3,396K
I/O read	0s	0.01s	+0.01s
I/O write	0s	0s	0s
Parse time	0.19s	0.3s	+0.11s
Bind time	0.07s	0.11s	+0.04s
Check time	0.82s	1.26s	+0.44s
Emit time	0s	0s	0s
Total time	1.08s	1.67s	+0.59s

Compiler Diagnostics (typescript-go)

	main (95eb860)	#5221 (156878b)	+/-
Files	215	215	0
Lines	121,006	121,008	+2
Identifiers	107,352	107,353	+1
Symbols	181,164	181,164	0
Types	262,348	262,348	0
Instantiations	621,588	621,588	0
Memory used	154,110K	154,076K	-34K
Memory allocs	1,784,037	1,783,986	-51
Config time	0.001s	0.001s	0s
BuildInfo read time	0s	0s	0s
Parse time	0.053s	0.094s	+0.041s
Bind time	0s	0s	0s
Check time	0.289s	0.459s	+0.17s
Emit time	0.003s	0.004s	+0.001s
Changes compute time	0.015s	0.036s	+0.021s
Total time	0.382s	0.629s	+0.247s

---

Reported by octocov

[github-actions]

HTTP Performance Benchmark

Framework	Runtime	Average	Ping	Query	Body
hono (origin/main)	bun	35,410.78	48,934.60	31,954.58	25,343.16
hono (current)	bun	35,642.95	49,025.56	31,965.47	25,937.82
Change		+0.66%	+0.19%	+0.03%	+2.35%

[yusukebe]

Hey @usualoma

I am planing introuce Mount Middleware and depracate app.mount now in v4 and, obsolute app.mount in v5.

I think it's okay to obsolete app.mount completely in v5 because app.mount is not used in many cases, and it's not so difficult to follow the new API.

So, please review this! If you have an opinion about the breaking change, feel free to share.

[usualoma]

Thank you. LGTM!

[yusukebe]

@usualoma Thanks!