From 633ec12956fa0b85829c93e18d46f466ce064c7d Mon Sep 17 00:00:00 2001
From: Kanta <dankodaa@gmail.com>
Date: Fri, 22 Jan 2021 18:46:14 +0900
Subject: [PATCH 1/2] Fix shallow routing scroll

---
 packages/next/next-server/lib/router/router.ts    |  5 ++++-
 .../pages/nav/shallow-routing.js                  |  4 +++-
 .../client-navigation/test/index.test.js          | 15 +++++++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/packages/next/next-server/lib/router/router.ts b/packages/next/next-server/lib/router/router.ts
index c5f464b15f08ff2..6238e1c139aaea0 100644
--- a/packages/next/next-server/lib/router/router.ts
+++ b/packages/next/next-server/lib/router/router.ts
@@ -1093,13 +1093,16 @@ export default class Router implements BaseRouter {
           !(routeInfo.Component as any).getInitialProps
       }
 
+      // shallow routing is only allowed for same page URL changes.
+      const isValidShallowRoute = options.shallow && this.route === route
       await this.set(
         route,
         pathname!,
         query,
         cleanedAs,
         routeInfo,
-        forcedScroll || (options.scroll ? { x: 0, y: 0 } : null)
+        forcedScroll ||
+          (isValidShallowRoute || !options.scroll ? null : { x: 0, y: 0 })
       ).catch((e) => {
         if (e.cancelled) error = error || e
         else throw e
diff --git a/test/integration/client-navigation/pages/nav/shallow-routing.js b/test/integration/client-navigation/pages/nav/shallow-routing.js
index 61dc8032249c1fb..7d41faa1df8bf54 100644
--- a/test/integration/client-navigation/pages/nav/shallow-routing.js
+++ b/test/integration/client-navigation/pages/nav/shallow-routing.js
@@ -35,7 +35,9 @@ export default class extends Component {
             Home
           </a>
         </Link>
-        <div id="counter">Counter: {this.getCurrentCounter()}</div>
+        <div id="counter" style={{ marginBottom: 4000 }}>
+          Counter: {this.getCurrentCounter()}
+        </div>
         <div id="get-initial-props-run-count">
           getInitialProps run count: {this.props.getInitialPropsRunCount}
         </div>
diff --git a/test/integration/client-navigation/test/index.test.js b/test/integration/client-navigation/test/index.test.js
index d6c00e0bbfd57f7..e3b951a3927e7b9 100644
--- a/test/integration/client-navigation/test/index.test.js
+++ b/test/integration/client-navigation/test/index.test.js
@@ -854,6 +854,21 @@ describe('Client Navigation', () => {
 
       await browser.close()
     })
+
+    it('should keep the scroll position on shallow routing', async () => {
+      const browser = await webdriver(context.appPort, '/nav/shallow-routing')
+      await browser.eval(() =>
+        document.querySelector('#increase').scrollIntoView()
+      )
+      const scrollPosition = await browser.eval('window.pageYOffset')
+
+      const newScrollPosition = await browser
+        .elementByCss('#increase')
+        .click()
+        .eval('window.pageYOffset')
+
+      expect(newScrollPosition).toBe(scrollPosition)
+    })
   })
 
   describe('with URL objects', () => {

From 50d28b2a22fe8d1d320595317f06dc1ceb7f33df Mon Sep 17 00:00:00 2001
From: Joe Haddad <joe.haddad@zeit.co>
Date: Fri, 22 Jan 2021 12:34:55 -0500
Subject: [PATCH 2/2] new tests

---
 .../pages/nav/shallow-routing.js              | 17 +++++++++++
 .../client-navigation/test/index.test.js      | 28 ++++++++++++++++---
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/test/integration/client-navigation/pages/nav/shallow-routing.js b/test/integration/client-navigation/pages/nav/shallow-routing.js
index 7d41faa1df8bf54..728467f9afde42b 100644
--- a/test/integration/client-navigation/pages/nav/shallow-routing.js
+++ b/test/integration/client-navigation/pages/nav/shallow-routing.js
@@ -27,6 +27,17 @@ export default class extends Component {
     Router.push(href, href, { shallow: true })
   }
 
+  increaseNonShallow() {
+    const counter = this.getCurrentCounter()
+    const href = `/nav/shallow-routing?counter=${counter + 1}`
+    Router.push(href, href, {})
+  }
+
+  gotoNavShallow() {
+    const href = `/nav`
+    Router.push(href, href, { shallow: true })
+  }
+
   render() {
     return (
       <div className="shallow-routing">
@@ -44,6 +55,12 @@ export default class extends Component {
         <button id="increase" onClick={() => this.increase()}>
           Increase
         </button>
+        <button id="increase2" onClick={() => this.increaseNonShallow()}>
+          Increase Non-Shallow
+        </button>
+        <button id="invalidShallow" onClick={() => this.gotoNavShallow()}>
+          Invalid Shallow Nav
+        </button>
       </div>
     )
   }
diff --git a/test/integration/client-navigation/test/index.test.js b/test/integration/client-navigation/test/index.test.js
index e3b951a3927e7b9..0d87cdeda148056 100644
--- a/test/integration/client-navigation/test/index.test.js
+++ b/test/integration/client-navigation/test/index.test.js
@@ -862,12 +862,32 @@ describe('Client Navigation', () => {
       )
       const scrollPosition = await browser.eval('window.pageYOffset')
 
-      const newScrollPosition = await browser
-        .elementByCss('#increase')
-        .click()
-        .eval('window.pageYOffset')
+      expect(scrollPosition).toBeGreaterThan(3000)
+
+      await browser.elementByCss('#increase').click()
+      await waitFor(500)
+      const newScrollPosition = await browser.eval('window.pageYOffset')
 
       expect(newScrollPosition).toBe(scrollPosition)
+
+      await browser.elementByCss('#increase2').click()
+      await waitFor(500)
+      const newScrollPosition2 = await browser.eval('window.pageYOffset')
+
+      expect(newScrollPosition2).toBe(0)
+
+      await browser.eval(() =>
+        document.querySelector('#invalidShallow').scrollIntoView()
+      )
+      const scrollPositionDown = await browser.eval('window.pageYOffset')
+
+      expect(scrollPositionDown).toBeGreaterThan(3000)
+
+      await browser.elementByCss('#invalidShallow').click()
+      await waitFor(500)
+      const newScrollPosition3 = await browser.eval('window.pageYOffset')
+
+      expect(newScrollPosition3).toBe(0)
     })
   })