Add NavigationManager.GetUriWithHash() extension method

src/Components/Components/src/NavigationManagerExtensions.cs

@@ -762,4 +762,74 @@ private static bool TryRebuildExistingQueryFromUri(
 
         return true;
     }
+
+    /// <summary>
+    /// Returns a URI constructed from <see cref="NavigationManager.Uri"/> with a hash
+    /// added, updated, or removed.
+    /// </summary>
+    /// <param name="navigationManager">The <see cref="NavigationManager"/>.</param>
+    /// <param name="hash">The hash string. If empty, the hash will be removed from the URI.</param>
+    /// <returns>The URI with the specified hash.</returns>
+    /// <remarks>
+    /// <para>
+    /// If <paramref name="hash"/> does not start with <c>#</c>, then <c>#</c> will be prepended.
+    /// </para>
+    /// <para>
+    /// This method is useful when the document's <c>baseURI</c> differs from its location,
+    /// such as when a <c>&lt;base&gt;</c> element is used, since relative hash URLs are resolved
+    /// relative to the <c>baseURI</c>.
+    /// </para>
+    /// <example>
+    /// <code>
+    /// @inject NavigationManager Nav
+    /// &lt;a href="@Nav.GetUriWithHash("section1")"&gt;Go to section 1&lt;/a&gt;
+    /// </code>
+    /// </example>
+    /// </remarks>
+    public static string GetUriWithHash(this NavigationManager navigationManager, string hash)
+    {
+        ArgumentNullException.ThrowIfNull(navigationManager);
+        ArgumentNullException.ThrowIfNull(hash);
+
+        var uri = navigationManager.Uri;
+        var existingHashIndex = uri.IndexOf('#');
+
+        // Determine the length of the URI without the existing hash
+        var uriWithoutHashLength = existingHashIndex < 0 ? uri.Length : existingHashIndex;
+
+        if (hash.Length == 0)
+        {
+            // If removing hash and there wasn't one, return original URI
+            if (existingHashIndex < 0)
+            {
+                return uri;
+            }
+
+            // Return just the URI part without hash
+            return uri.Substring(0, uriWithoutHashLength);
+        }
+
+        var hashStartsWithSymbol = hash[0] == '#';
+
+        // Calculate the total length needed
+        var totalLength = uriWithoutHashLength + (hashStartsWithSymbol ? hash.Length : hash.Length + 1);
+
+        return string.Create(totalLength, (uri, hash, uriWithoutHashLength, hashStartsWithSymbol), static (chars, state) =>
+        {
+            var (uriValue, hashValue, uriLength, startsWithSymbol) = state;
+
+            // Copy URI without hash
+            uriValue.AsSpan(0, uriLength).CopyTo(chars);
+            var position = uriLength;
+
+            // Add '#' if hash doesn't start with one
+            if (!startsWithSymbol)
+            {
+                chars[position++] = '#';
+            }
+
+            // Copy hash
+            hashValue.AsSpan().CopyTo(chars[position..]);
+        });
+    }
 }

src/Components/Components/src/PublicAPI.Unshipped.txt

@@ -1,4 +1,5 @@
 #nullable enable
+static Microsoft.AspNetCore.Components.NavigationManagerExtensions.GetUriWithHash(this Microsoft.AspNetCore.Components.NavigationManager! navigationManager, string! hash) -> string!
 Microsoft.AspNetCore.Components.NavigationOptions.RelativeToCurrentUri.get -> bool
 Microsoft.AspNetCore.Components.NavigationOptions.RelativeToCurrentUri.init -> void
 Microsoft.AspNetCore.Components.IComponentPropertyActivator

src/Components/Components/test/NavigationManagerTest.cs

@@ -213,6 +213,62 @@ public void GetUriWithQueryParameters_ThrowsWhenAnyParameterNameIsEmpty(string b
         Assert.StartsWith("Cannot have empty query parameter names.", exception.Message);
     }
 
+    [Theory]
+    [InlineData("scheme://host/", "section1", "scheme://host/#section1")]
+    [InlineData("scheme://host/", "#section1", "scheme://host/#section1")]
+    [InlineData("scheme://host/path", "section1", "scheme://host/path#section1")]
+    [InlineData("scheme://host/path/", "section1", "scheme://host/path/#section1")]
+    [InlineData("scheme://host/path?query=value", "section1", "scheme://host/path?query=value#section1")]
+    [InlineData("scheme://host/path?query=value#oldHash", "section1", "scheme://host/path?query=value#section1")]
+    [InlineData("scheme://host/path#oldHash", "newHash", "scheme://host/path#newHash")]
+    [InlineData("scheme://host/path#old", "#new", "scheme://host/path#new")]
+    // Tests with non-root base paths (e.g., when using <base href="/subdir/">)
+    [InlineData("scheme://host/subdir/page", "section1", "scheme://host/subdir/page#section1")]
+    [InlineData("scheme://host/subdir/page", "#section1", "scheme://host/subdir/page#section1")]
+    [InlineData("scheme://host/subdir/page#old", "section1", "scheme://host/subdir/page#section1")]
+    [InlineData("scheme://host/app/subdir/page?query=value", "section1", "scheme://host/app/subdir/page?query=value#section1")]
+    public void GetUriWithHash_AddsOrReplacesHash(string baseUri, string hash, string expectedUri)
+    {
+        var navigationManager = new TestNavigationManager(baseUri);
+        var actualUri = navigationManager.GetUriWithHash(hash);
+
+        Assert.Equal(expectedUri, actualUri);
+    }
+
+    [Theory]
+    [InlineData("scheme://host/", "scheme://host/")]
+    [InlineData("scheme://host/path", "scheme://host/path")]
+    [InlineData("scheme://host/path#hash", "scheme://host/path")]
+    [InlineData("scheme://host/path?query=value#hash", "scheme://host/path?query=value")]
+    // Tests with non-root base paths (e.g., when using <base href="/subdir/">)
+    [InlineData("scheme://host/subdir/page#hash", "scheme://host/subdir/page")]
+    [InlineData("scheme://host/app/subdir/page?query=value#hash", "scheme://host/app/subdir/page?query=value")]
+    public void GetUriWithHash_RemovesHashWhenHashIsEmpty(string baseUri, string expectedUri)
+    {
+        var navigationManager = new TestNavigationManager(baseUri);
+
+        var actualUriWithEmpty = navigationManager.GetUriWithHash(string.Empty);
+        Assert.Equal(expectedUri, actualUriWithEmpty);
+    }
+
+    [Fact]
+    public void GetUriWithHash_ThrowsWhenNavigationManagerIsNull()
+    {
+        NavigationManager navigationManager = null;
+
+        var exception = Assert.Throws<ArgumentNullException>(() => navigationManager.GetUriWithHash("hash"));
+        Assert.Equal("navigationManager", exception.ParamName);
+    }
+
+    [Fact]
+    public void GetUriWithHash_ThrowsWhenHashIsNull()
+    {
+        var navigationManager = new TestNavigationManager("scheme://host/");
+
+        var exception = Assert.Throws<ArgumentNullException>(() => navigationManager.GetUriWithHash(null));
+        Assert.Equal("hash", exception.ParamName);
+    }
+
     [Fact]
     public void LocationChangingHandlers_CanContinueTheNavigationSynchronously_WhenOneHandlerIsRegistered()
     {