Add test for link back to original page (vercel#41297)

- Implements failing test
- Implemented handling for the case where the router tree does not match up with the segment path being navigated to. This is what caused the underlying error. 



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `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`
- [ ] Integration 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`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

packages/next/client/components/reducer.ts

@@ -471,11 +471,16 @@ function shouldHardNavigate(
     string
   ]
 
-  // If dynamic parameter in tree doesn't match up with segment path a hard navigation is triggered.
-  if (Array.isArray(currentSegment) && !matchSegment(currentSegment, segment)) {
-    return true
-  }
+  // Check if current segment matches the existing segment.
+  if (!matchSegment(currentSegment, segment)) {
+    // If dynamic parameter in tree doesn't match up with segment path a hard navigation is triggered.
+    if (Array.isArray(currentSegment)) {
+      return true
+    }
 
+    // If the existing segment did not match soft navigation is triggered.
+    return false
+  }
   const lastSegment = flightSegmentPath.length <= 2
 
   if (lastSegment) {

test/e2e/app-dir/app/app/linking/about/page.js

@@ -0,0 +1,3 @@
+export default function AboutPage() {
+  return <p id="about-page">About page</p>
+}

test/e2e/app-dir/app/app/linking/layout.js

@@ -0,0 +1,15 @@
+import Link from 'next/link'
+
+export default function Layout({ children }) {
+  return (
+    <>
+      <header>
+        <nav>
+          <Link href="/linking">Home</Link>
+          <Link href="/linking/about">About</Link>
+        </nav>
+      </header>
+      {children}
+    </>
+  )
+}

test/e2e/app-dir/app/app/linking/page.js

@@ -0,0 +1,3 @@
+export default function Page() {
+  return <p id="home-page">Home page</p>
+}

test/e2e/app-dir/index.test.ts

@@ -1570,6 +1570,24 @@ describe('app dir', () => {
             .text()
         ).toBe(`hello from app/dashboard/deployments/info/[id]. ID is: 123`)
       })
+      it('should handle next/link back to initially loaded page', async () => {
+        const browser = await webdriver(next.url, '/linking/about')
+        expect(
+          await browser
+            .elementByCss('a[href="/linking"]')
+            .click()
+            .waitForElementByCss('#home-page')
+            .text()
+        ).toBe(`Home page`)
+
+        expect(
+          await browser
+            .elementByCss('a[href="/linking/about"]')
+            .click()
+            .waitForElementByCss('#about-page')
+            .text()
+        ).toBe(`About page`)
+      })
     })
 
     describe('not-found', () => {