fix(app): app.mount() supports / (#1119)

* fix(app): `app.mount()` supports `/`

* chore: denoify

deno_dist/hono-base.ts

@@ -205,7 +205,9 @@ class Hono<E extends Env = Env, S = {}, BasePath extends string = '/'> extends d
     applicationHandler: (request: Request, ...args: any) => Response | Promise<Response>,
     optionHandler?: (c: Context) => unknown
   ): Hono<E, S, BasePath> {
-    const pathPrefixLength = mergePath(this._basePath, path).length
+    const mergedPath = mergePath(this._basePath, path)
+    const pathPrefixLength = mergedPath === '/' ? 0 : mergedPath.length
+
     const handler: MiddlewareHandler = async (c, next) => {
       let executionContext: ExecutionContext | undefined = undefined
       try {

src/hono-base.ts

@@ -205,7 +205,9 @@ class Hono<E extends Env = Env, S = {}, BasePath extends string = '/'> extends d
     applicationHandler: (request: Request, ...args: any) => Response | Promise<Response>,
     optionHandler?: (c: Context) => unknown
   ): Hono<E, S, BasePath> {
-    const pathPrefixLength = mergePath(this._basePath, path).length
+    const mergedPath = mergePath(this._basePath, path)
+    const pathPrefixLength = mergedPath === '/' ? 0 : mergedPath.length
+
     const handler: MiddlewareHandler = async (c, next) => {
       let executionContext: ExecutionContext | undefined = undefined
       try {

src/hono.test.ts

@@ -1916,7 +1916,6 @@ describe('app.mount()', () => {
   describe('Basic', () => {
     const anotherApp = (req: Request, params: unknown) => {
       const path = getPath(req)
-      console.log(`path in anotherApp: ${path}`)
       if (path === '/') {
         return new Response('AnotherApp')
       }
@@ -1939,7 +1938,6 @@ describe('app.mount()', () => {
           }
         )
       }
-      console.log(`before 404 ${req.url}`)
       return new Response('Not Found from AnotherApp', {
         status: 404,
       })
@@ -2065,6 +2063,42 @@ describe('app.mount()', () => {
       })
     })
   })
+
+  describe('Mount on `/`', () => {
+    const anotherApp = (req: Request, params: unknown) => {
+      const path = getPath(req)
+      if (path === '/') {
+        return new Response('AnotherApp')
+      }
+      if (path === '/hello') {
+        return new Response('Hello from AnotherApp')
+      }
+      if (path === '/good/night') {
+        return new Response('Good Night from AnotherApp')
+      }
+      return new Response('Not Found from AnotherApp', {
+        status: 404,
+      })
+    }
+
+    const app = new Hono()
+    app.mount('/', anotherApp)
+
+    it('Should return responses from AnotherApp - mount on `/`', async () => {
+      let res = await app.request('/')
+      expect(res.status).toBe(200)
+      expect(await res.text()).toBe('AnotherApp')
+      res = await app.request('/hello')
+      expect(res.status).toBe(200)
+      expect(await res.text()).toBe('Hello from AnotherApp')
+      res = await app.request('/good/night')
+      expect(res.status).toBe(200)
+      expect(await res.text()).toBe('Good Night from AnotherApp')
+      res = await app.request('/not-found')
+      expect(res.status).toBe(404)
+      expect(await res.text()).toBe('Not Found from AnotherApp')
+    })
+  })
 })
 
 describe('Router Name', () => {