Scroll in enhanced navigation behaves same as in client side routing

src/Components/Web.JS/src/Rendering/Renderer.ts

@@ -95,7 +95,7 @@ export function resetScrollAfterNextBatch(): void {
   shouldResetScrollAfterNextBatch = true;
 }
 
-function resetScrollIfNeeded() {
+export function resetScrollIfNeeded() {
   if (shouldResetScrollAfterNextBatch) {
     shouldResetScrollAfterNextBatch = false;
 

src/Components/Web.JS/src/Services/NavigationEnhancement.ts

@@ -3,6 +3,7 @@
 
 import { synchronizeDomContent } from '../Rendering/DomMerging/DomSync';
 import { attachProgrammaticEnhancedNavigationHandler, handleClickForNavigationInterception, hasInteractiveRouter, isForSamePath, isSamePageWithHash, notifyEnhancedNavigationListeners, performScrollToElementOnTheSamePage } from './NavigationUtils';
+import { resetScrollAfterNextBatch, resetScrollIfNeeded } from '../Rendering/Renderer';
 
 /*
 In effect, we have two separate client-side navigation mechanisms:
@@ -70,13 +71,19 @@ export function detachProgressivelyEnhancedNavigationListener() {
   window.removeEventListener('popstate', onPopState);
 }
 
-function performProgrammaticEnhancedNavigation(absoluteInternalHref: string, replace: boolean) {
+function performProgrammaticEnhancedNavigation(absoluteInternalHref: string, replace: boolean) : void {
+  const originalLocation = location.href;
+
   if (replace) {
     history.replaceState(null, /* ignored title */ '', absoluteInternalHref);
   } else {
     history.pushState(null, /* ignored title */ '', absoluteInternalHref);
   }
 
+  if (!isForSamePath(absoluteInternalHref, originalLocation)) {
+    resetScrollAfterNextBatch();
+  }
+
   performEnhancedPageLoad(absoluteInternalHref, /* interceptedLink */ false);
 }
 
@@ -90,13 +97,20 @@ function onDocumentClick(event: MouseEvent) {
   }
 
   handleClickForNavigationInterception(event, absoluteInternalHref => {
+    const originalLocation = location.href;
+
     const shouldScrollToHash = isSamePageWithHash(absoluteInternalHref);
     history.pushState(null, /* ignored title */ '', absoluteInternalHref);
 
     if (shouldScrollToHash) {
       performScrollToElementOnTheSamePage(absoluteInternalHref);
     } else {
+      let isSelfNavigation = isForSamePath(absoluteInternalHref, originalLocation);
       performEnhancedPageLoad(absoluteInternalHref, /* interceptedLink */ true);
+      if (!isSelfNavigation) {
+        resetScrollAfterNextBatch();
+        resetScrollIfNeeded();
+      }
     }
   });
 }
@@ -106,6 +120,7 @@ function onPopState(state: PopStateEvent) {
     return;
   }
 
+  // load the new page
   performEnhancedPageLoad(location.href, /* interceptedLink */ false);
 }
 

src/Components/test/E2ETest/Infrastructure/WebDriverExtensions/WebDriverExtensions.cs

@@ -2,16 +2,70 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using OpenQA.Selenium;
+using OpenQA.Selenium.Support.UI;
+using System;
 
 namespace Microsoft.AspNetCore.Components.E2ETest;
 
 internal static class WebDriverExtensions
 {
+    private static string GetFindPositionScript(string elementId) =>
+        $"return Math.round(document.getElementById('{elementId}').getBoundingClientRect().top + window.scrollY);";
+
     public static void Navigate(this IWebDriver browser, Uri baseUri, string relativeUrl)
     {
         var absoluteUrl = new Uri(baseUri, relativeUrl);
 
         browser.Navigate().GoToUrl("about:blank");
         browser.Navigate().GoToUrl(absoluteUrl);
     }
+
+    public static void WaitForElementToBeVisible(this IWebDriver browser, By by, int timeoutInSeconds = 5)
+    {
+        var wait = new DefaultWait<IWebDriver>(browser)
+        {
+            Timeout = TimeSpan.FromSeconds(timeoutInSeconds),
+            PollingInterval = TimeSpan.FromMilliseconds(100)
+        };
+        wait.IgnoreExceptionTypes(typeof(NoSuchElementException), typeof(StaleElementReferenceException));
+        wait.Until(driver =>
+        {
+            try
+            {
+                var element = driver.FindElement(by);
+                return element.Displayed;
+            }
+            catch (StaleElementReferenceException)
+            {
+                // Retry finding the element
+                return false;
+            }
+        });
+    }
+
+    public static long GetElementPositionWithRetry(this IWebDriver browser, string elementId, int retryCount = 3, int delayBetweenRetriesMs = 100)
+    {
+        var jsExecutor = (IJavaScriptExecutor)browser;
+        string script = GetFindPositionScript(elementId);
+        browser.WaitForElementToBeVisible(By.Id(elementId));
+        for (int i = 0; i < retryCount; i++)
+        {
+            try
+            {
+                var result = jsExecutor.ExecuteScript(script);
+                if (result != null)
+                {
+                    return (long)result;
+                }
+            }
+            catch (OpenQA.Selenium.JavaScriptException)
+            {
+                // JavaScript execution failed, retry
+            }
+
+            Thread.Sleep(delayBetweenRetriesMs);
+        }
+
+        throw new Exception($"Failed to execute script after {retryCount} retries.");
+    }
 }

src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTest.cs

@@ -1,14 +1,18 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
+using System.Threading.Tasks;
+using Components.TestServer.RazorComponents;
+using Microsoft.AspNetCore.Components.E2ETest;
 using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
 using Microsoft.AspNetCore.E2ETesting;
-using TestServer;
-using Xunit.Abstractions;
-using Components.TestServer.RazorComponents;
 using OpenQA.Selenium;
+using OpenQA.Selenium.BiDi.Communication;
 using OpenQA.Selenium.Support.Extensions;
+using TestServer;
+using Xunit.Abstractions;
+using Xunit.Sdk;
 
 namespace Microsoft.AspNetCore.Components.E2ETests.ServerRenderingTests;
 
@@ -662,6 +666,203 @@ public void CanUpdateHrefOnLinkTagWithIntegrity()
         Browser.Equal("rgba(0, 0, 255, 1)", () => originalH1Elem.GetCssValue("color"));
     }
 
+    [Theory]
+    [InlineData(false, false, false)]
+    [InlineData(false, true, false)]
+    [InlineData(true, true, false)]
+    [InlineData(true, false, false)]
+    // [InlineData(false, false, true)] programmatic navigation doesn't work without enhanced navigation
+    [InlineData(false, true, true)]
+    [InlineData(true, true, true)]
+    // [InlineData(true, false, true)] programmatic navigation doesn't work without enhanced navigation
+    public void EnhancedNavigationScrollBehavesSameAsBrowserOnNavigation(bool enableStreaming, bool useEnhancedNavigation, bool programmaticNavigation)
+    {
+        // This test checks if the navigation to another path moves the scroll to the top of the page,
+        // or to the beginning of a fragment, regardless of the previous scroll position
+        string landingPageSuffix = enableStreaming ? "" : "-no-streaming";
+        string buttonKeyword = programmaticNavigation ? "-programmatic" : "";
+        Navigate($"{ServerPathBase}/nav/scroll-test{landingPageSuffix}");
+        EnhancedNavigationTestUtil.SuppressEnhancedNavigation(this, shouldSuppress: !useEnhancedNavigation, skipNavigation: true);
+
+        // "landing" page: scroll maximally down and go to "next" page - we should land at the top of that page
+        AssertWeAreOnLandingPage();
+
+        // staleness check is used to assert enhanced navigation is enabled/disabled, as requested
+        var elementForStalenessCheckOnNextPage = Browser.Exists(By.TagName("html"));
+
+        var button1Id = $"do{buttonKeyword}-navigation";
+        var button1Pos = Browser.GetElementPositionWithRetry(button1Id);
+        Browser.SetScrollY(button1Pos);
+        Browser.Exists(By.Id(button1Id)).Click();
+
+        // "next" page: check if we landed at 0, then navigate to "landing"
+        AssertWeAreOnNextPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        string fragmentId = "some-content";
+        Browser.WaitForElementToBeVisible(By.Id(fragmentId));
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnNextPage);
+        Assert.Equal(0, Browser.GetScrollY());
+        var elementForStalenessCheckOnLandingPage = Browser.Exists(By.TagName("html"));
+        var fragmentScrollPosition = Browser.GetElementPositionWithRetry(fragmentId);
+        Browser.Exists(By.Id(button1Id)).Click();
+
+        // "landing" page: navigate to a fragment on another page - we should land at the beginning of the fragment
+        AssertWeAreOnLandingPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnLandingPage);
+
+        var button2Id = $"do{buttonKeyword}-navigation-with-fragment";
+        Browser.Exists(By.Id(button2Id)).Click();
+        AssertWeAreOnNextPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnNextPage);
+        var expectedFragmentScrollPosition = fragmentScrollPosition - 1;
+        Assert.Equal(expectedFragmentScrollPosition, Browser.GetScrollY());
+    }
+
+    [Theory]
+    [InlineData(false, false, false)]
+    [InlineData(false, true, false)]
+    [InlineData(true, true, false)]
+    [InlineData(true, false, false)]
+    // [InlineData(false, false, true)] programmatic navigation doesn't work without enhanced navigation
+    [InlineData(false, true, true)]
+    [InlineData(true, true, true)]
+    // [InlineData(true, false, true)] programmatic navigation doesn't work without enhanced navigation
+    public void EnhancedNavigationScrollBehavesSameAsBrowserOnBackwardsForwardsAction(bool enableStreaming, bool useEnhancedNavigation, bool programmaticNavigation)
+    {
+        // This test checks if the scroll position is preserved after backwards/forwards action
+        string landingPageSuffix = enableStreaming ? "" : "-no-streaming";
+        string buttonKeyword = programmaticNavigation ? "-programmatic" : "";
+        Navigate($"{ServerPathBase}/nav/scroll-test{landingPageSuffix}");
+        EnhancedNavigationTestUtil.SuppressEnhancedNavigation(this, shouldSuppress: !useEnhancedNavigation, skipNavigation: true);
+
+        // "landing" page: scroll to pos1, navigate away
+        AssertWeAreOnLandingPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+
+        // staleness check is used to assert enhanced navigation is enabled/disabled, as requested
+        var elementForStalenessCheckOnNextPage = Browser.Exists(By.TagName("html"));
+
+        var buttonId = $"do{buttonKeyword}-navigation";
+        Browser.WaitForElementToBeVisible(By.Id(buttonId));
+        var landingPagePos1 = Browser.GetElementPositionWithRetry(buttonId) - 100;
+        Browser.SetScrollY(landingPagePos1);
+        Browser.Exists(By.Id(buttonId)).Click();
+
+        // "next" page: scroll to pos1, navigate away
+        AssertWeAreOnNextPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        Browser.WaitForElementToBeVisible(By.Id(buttonId));
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnNextPage);
+        var elementForStalenessCheckOnLandingPage = Browser.Exists(By.TagName("html"));
+        var nextPagePos1 = Browser.GetElementPositionWithRetry(buttonId) - 100;
+        // make sure we are expecting different scroll positions on the 1st and the 2nd page
+        Assert.NotEqual(landingPagePos1, nextPagePos1);
+        Browser.SetScrollY(nextPagePos1);
+        Browser.Exists(By.Id(buttonId)).Click();
+
+        // "landing" page: scroll to pos2, go backwards
+        AssertWeAreOnLandingPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnLandingPage);
+        var landingPagePos2 = 500;
+        Browser.SetScrollY(landingPagePos2);
+        Browser.Navigate().Back();
+
+        // "next" page: check if we landed on pos1, move the scroll to pos2, go backwards
+        AssertWeAreOnNextPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnNextPage);
+        AssertScrollPositionCorrect(useEnhancedNavigation, nextPagePos1);
+
+        var nextPagePos2 = 600;
+        Browser.SetScrollY(nextPagePos2);
+        Browser.Navigate().Back();
+
+        // "landing" page: check if we landed on pos1, move the scroll to pos3, go forwards
+        AssertWeAreOnLandingPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnLandingPage);
+        AssertScrollPositionCorrect(useEnhancedNavigation, landingPagePos1);
+        var landingPagePos3 = 700;
+        Browser.SetScrollY(landingPagePos3);
+        Browser.Navigate().Forward();
+
+        // "next" page: check if we landed on pos1, go forwards
+        AssertWeAreOnNextPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnNextPage);
+        AssertScrollPositionCorrect(useEnhancedNavigation, nextPagePos2);
+        Browser.Navigate().Forward();
+
+        // "scroll" page: check if we landed on pos2
+        AssertWeAreOnLandingPage();
+        WaitStreamingRendersFullPage(enableStreaming);
+        AssertEnhancedNavigation(useEnhancedNavigation, elementForStalenessCheckOnLandingPage);
+        AssertScrollPositionCorrect(useEnhancedNavigation, landingPagePos2);
+    }
+
+    private void AssertScrollPositionCorrect(bool useEnhancedNavigation, long previousScrollPosition)
+    {
+        // from some reason, scroll position sometimes differs by 1 pixel between enhanced and browser's navigation
+        // browser's navigation is not precisely going backwards/forwards to the previous state
+        var currentScrollPosition = Browser.GetScrollY();
+        string messagePart = useEnhancedNavigation ? $"{previousScrollPosition}" : $"{previousScrollPosition} or {previousScrollPosition - 1}";
+        bool isPreciselyWhereItWasLeft = currentScrollPosition == previousScrollPosition;
+        bool isPixelLowerThanItWasLeft = currentScrollPosition == (previousScrollPosition - 1);
+        bool success = useEnhancedNavigation
+            ? isPreciselyWhereItWasLeft
+            : (isPreciselyWhereItWasLeft || isPixelLowerThanItWasLeft);
+        Assert.True(success, $"The expected scroll position was {messagePart}, but it was found at {currentScrollPosition}.");
+    }
+
+    private void AssertEnhancedNavigation(bool useEnhancedNavigation, IWebElement elementForStalenessCheck, int retryCount = 3, int delayBetweenRetriesMs = 100)
+    {
+        bool enhancedNavigationDetected = false;
+        for (int i = 0; i < retryCount; i++)
+        {
+            try
+            {
+                enhancedNavigationDetected = !IsElementStale(elementForStalenessCheck);
+                Assert.Equal(useEnhancedNavigation, enhancedNavigationDetected);
+                return;
+            }
+            catch (XunitException)
+            {
+                // Maybe the check was done too early to change the DOM ref, retry
+            }
+
+            Thread.Sleep(delayBetweenRetriesMs);
+        }
+        string expectedNavigation = useEnhancedNavigation ? "enhanced navigation" : "browser navigation";
+        string isStale = enhancedNavigationDetected ? "is not stale" : "is stale";
+        var isNavigationSupressed = (string)((IJavaScriptExecutor)Browser).ExecuteScript("return sessionStorage.getItem('suppress-enhanced-navigation');");
+        throw new Exception($"Expected to use {expectedNavigation} because 'suppress-enhanced-navigation' is set to {isNavigationSupressed} but the element from previous path {isStale}");
+    }
+
+    private void AssertWeAreOnLandingPage()
+    {
+        string infoName = "test-info-1";
+        Browser.WaitForElementToBeVisible(By.Id(infoName), timeoutInSeconds: 20);
+        Browser.Equal("Scroll tests landing page", () => Browser.Exists(By.Id(infoName)).Text);
+    }
+
+    private void AssertWeAreOnNextPage()
+    {
+        string infoName = "test-info-2";
+        Browser.WaitForElementToBeVisible(By.Id(infoName), timeoutInSeconds: 20);
+        Browser.Equal("Scroll tests next page", () => Browser.Exists(By.Id(infoName)).Text);
+    }
+
+    private void WaitStreamingRendersFullPage(bool enableStreaming)
+    {
+        if (enableStreaming)
+        {
+            Browser.WaitForElementToBeVisible(By.Id("some-content"));
+        }
+    }
+
     private void AssertEnhancedUpdateCountEquals(long count)
         => Browser.Equal(count, () => ((IJavaScriptExecutor)Browser).ExecuteScript("return window.enhancedPageUpdateCount;"));
 

src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTestUtil.cs

@@ -32,4 +32,7 @@ public static void SuppressEnhancedNavigation<TServerFixture>(ServerTestBase<TSe
 
     public static long GetScrollY(this IWebDriver browser)
         => Convert.ToInt64(((IJavaScriptExecutor)browser).ExecuteScript("return window.scrollY"), CultureInfo.CurrentCulture);
+
+    public static long SetScrollY(this IWebDriver browser, long value)
+        => Convert.ToInt64(((IJavaScriptExecutor)browser).ExecuteScript($"window.scrollTo(0, {value})"), CultureInfo.CurrentCulture);
 }