Fix normalization of .rsc extension (#46043)

Fixes #45883
Fixes NEXT-541

The reason the url after normalization in middleware ended up being
`/somethingabc=def` instead of `/something?abc=def` is that the regex
matches `?` so the `?` will be removed. Since it's in a capture group
the only change needed was applying that by adding `$1` to the
replacement.

Added some unit tests for this function, going to add additional
integration tests now.

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## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ]
[e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs)
tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
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packages/next/src/shared/lib/router/utils/app-paths.test.ts

@@ -0,0 +1,22 @@
+import { normalizeRscPath } from './app-paths'
+
+describe('normalizeRscPath', () => {
+  describe('enabled', () => {
+    it('should normalize url with .rsc', () => {
+      expect(normalizeRscPath('/test.rsc', true)).toBe('/test')
+    })
+    it('should normalize url with .rsc and searchparams', () => {
+      expect(normalizeRscPath('/test.rsc?abc=def', true)).toBe('/test?abc=def')
+    })
+  })
+  describe('disabled', () => {
+    it('should normalize url with .rsc', () => {
+      expect(normalizeRscPath('/test.rsc', false)).toBe('/test.rsc')
+    })
+    it('should normalize url with .rsc and searchparams', () => {
+      expect(normalizeRscPath('/test.rsc?abc=def', false)).toBe(
+        '/test.rsc?abc=def'
+      )
+    })
+  })
+})

packages/next/src/shared/lib/router/utils/app-paths.ts

@@ -50,6 +50,16 @@ export function normalizeAppPath(route: string) {
   )
 }
 
+/**
+ * Strips the `.rsc` extension if it's in the pathname.
+ * Since this function is used on full urls it checks `?` for searchParams handling.
+ */
 export function normalizeRscPath(pathname: string, enabled?: boolean) {
-  return enabled ? pathname.replace(/\.rsc($|\?)/, '') : pathname
+  return enabled
+    ? pathname.replace(
+        /\.rsc($|\?)/,
+        // $1 ensures `?` is preserved
+        '$1'
+      )
+    : pathname
 }