Fix component end tags to behave consistently with start tags for Hover, Go To Definition, and Find All References

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Extensions/RazorCodeDocumentExtensions_ComponentEndTag.cs

@@ -0,0 +1,44 @@
+// 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.Razor.Language.Syntax;
+
+namespace Microsoft.AspNetCore.Razor.Language;
+
+internal static partial class RazorCodeDocumentExtensions
+{
+    /// <summary>
+    /// Adjusts the position if it's on a component end tag to use the corresponding start tag position.
+    /// This ensures that hover, go to definition, and find all references work consistently for both
+    /// start and end tags, since only start tags have source mappings.
+    /// </summary>
+    /// <param name="codeDocument">The code document.</param>
+    /// <param name="hostDocumentIndex">The position in the host document.</param>
+    /// <returns>
+    /// The adjusted position if on a component end tag's name, otherwise the original position.
+    /// </returns>
+    public static int AdjustPositionForComponentEndTag(this RazorCodeDocument codeDocument, int hostDocumentIndex)
+    {
+        var root = codeDocument.GetRequiredSyntaxRoot();
+        var owner = root.FindInnermostNode(hostDocumentIndex, includeWhitespace: false);
+        if (owner is null)
+        {
+            return hostDocumentIndex;
+        }
+
+        // Check if we're on a component end tag and the position is within the tag name
+        if (owner.FirstAncestorOrSelf<MarkupTagHelperEndTagSyntax>() is { } endTag &&
+            endTag.Name.Span.IntersectsWith(hostDocumentIndex) &&
+            endTag.GetStartTag() is MarkupTagHelperStartTagSyntax tagHelperStartTag)
+        {
+            // Calculate the offset within the end tag name
+            var offsetInEndTag = hostDocumentIndex - endTag.Name.SpanStart;
+
+            // Apply the same offset to the start tag name
+            // This preserves the relative position within the tag name
+            return tagHelperStartTag.Name.SpanStart + offsetInEndTag;
+        }
+
+        return hostDocumentIndex;
+    }
+}

src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/FindAllReferences/RemoteFindAllReferencesService.cs

@@ -3,6 +3,7 @@
 
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor;
 using Microsoft.CodeAnalysis.Razor;
 using Microsoft.CodeAnalysis.Razor.DocumentMapping;
@@ -55,6 +56,9 @@ protected override IRemoteFindAllReferencesService CreateService(in ServiceArgs
             return NoFurtherHandling;
         }
 
+        // Adjust position if on a component end tag to use the start tag position
+        hostDocumentIndex = codeDocument.AdjustPositionForComponentEndTag(hostDocumentIndex);
+
         var positionInfo = GetPositionInfo(codeDocument, hostDocumentIndex, preferCSharpOverHtml: true);
 
         if (positionInfo.LanguageKind is not RazorLanguageKind.CSharp)

src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/GoToDefinition/RemoteGoToDefinitionService.cs

@@ -3,6 +3,7 @@
 
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor;
 using Microsoft.CodeAnalysis.Razor.DocumentMapping;
@@ -54,6 +55,9 @@ protected override IRemoteGoToDefinitionService CreateService(in ServiceArgs arg
             return NoFurtherHandling;
         }
 
+        // Adjust position if on a component end tag to use the start tag position
+        hostDocumentIndex = codeDocument.AdjustPositionForComponentEndTag(hostDocumentIndex);
+
         var positionInfo = GetPositionInfo(codeDocument, hostDocumentIndex, preferCSharpOverHtml: true);
 
         // First, see if this is a tag helper. We ignore component attributes here, because they're better served by the C# handler.

src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/Hover/RemoteHoverService.cs

@@ -1,10 +1,12 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor;
+using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor;
 using Microsoft.CodeAnalysis.Razor.DocumentMapping;
 using Microsoft.CodeAnalysis.Razor.Hover;
@@ -46,11 +48,17 @@ protected override IRemoteHoverService CreateService(in ServiceArgs args)
     {
         var codeDocument = await context.GetCodeDocumentAsync(cancellationToken).ConfigureAwait(false);
 
-        if (!codeDocument.Source.Text.TryGetAbsoluteIndex(position, out var hostDocumentIndex))
+        var sourceText = codeDocument.Source.Text;
+        if (!sourceText.TryGetAbsoluteIndex(position, out var hostDocumentIndex))
         {
             return NoFurtherHandling;
         }
 
+        var originalHostDocumentIndex = hostDocumentIndex;
+
+        // Adjust position if on a component end tag to use the start tag position
+        hostDocumentIndex = codeDocument.AdjustPositionForComponentEndTag(hostDocumentIndex);
+
         var clientCapabilities = _clientCapabilitiesService.ClientCapabilities;
         var positionInfo = GetPositionInfo(codeDocument, hostDocumentIndex, preferCSharpOverHtml: true);
 
@@ -82,6 +90,27 @@ protected override IRemoteHoverService CreateService(in ServiceArgs args)
                 csharpHover.Range = LspFactory.CreateRange(hostDocumentSpan);
             }
 
+            // If we adjusted from an end tag to a start tag, we need to make sure the range covers the end tag,
+            // not just the start tag, or VS won't show the hover info
+            if (originalHostDocumentIndex > hostDocumentIndex &&
+                csharpHover.Range is not null)
+            {
+                // We were originally on the end tag somewhere, then redirected to the start tag to get the hover.
+                // We now need to translate the range we got back, and mapped, over to the end tag again. This is as
+                // easy as just offsetting the range by the difference between our original and adjusted index.
+                if (sourceText.TryGetAbsoluteIndex(csharpHover.Range.Start, out var adjustedStart) &&
+                    sourceText.TryGetAbsoluteIndex(csharpHover.Range.End, out var adjustedEnd))
+                {
+                    var offset = originalHostDocumentIndex - hostDocumentIndex;
+
+                    // Make sure we don't fall off the end of the document, though it should be impossible
+                    adjustedStart = Math.Min(adjustedStart + offset, sourceText.Length - 1);
+                    adjustedEnd = Math.Min(adjustedEnd + offset, sourceText.Length - 1);
+
+                    csharpHover.Range = sourceText.GetRange(adjustedStart, adjustedEnd);
+                }
+            }
+
             return Results(csharpHover);
         }
 

src/Razor/test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Cohost/CohostHoverEndpointTest.cs

@@ -73,6 +73,26 @@ public async Task Html()
         await VerifyHoverAsync(code, htmlResponse, h => Assert.Same(htmlResponse, h));
     }
 
+    [Fact]
+    public async Task Html_EndTag()
+    {
+        TestCode code = """
+            <PageTitle></PageTitle>
+            <div></d$$iv>
+
+            @{
+                var myVariable = "Hello";
+
+                var length = myVariable.Length;
+            }
+            """;
+
+        // This simply verifies that Hover will call into HTML.
+        var htmlResponse = new VSInternalHover();
+
+        await VerifyHoverAsync(code, htmlResponse, h => Assert.Same(htmlResponse, h));
+    }
+
     [Fact]
     public async Task CSharp()
     {
@@ -185,6 +205,111 @@ await VerifyHoverAsync(code, async (hover, document) =>
         });
     }
 
+    [Fact]
+    public async Task ComponentEndTag()
+    {
+        TestCode code = """
+            <PageTitle></[|Pa$$geTitle|]>
+            <div></div>
+
+            @{
+                var myVariable = "Hello";
+
+                var length = myVariable.Length;
+            }
+            """;
+
+        await VerifyHoverAsync(code, async (hover, document) =>
+        {
+            await hover.VerifyRangeAsync(code.Span, document);
+
+            hover.VerifyRawContent(
+                Container(
+                    Container(
+                        Image,
+                        ClassifiedText( // class Microsoft.AspNetCore.Components.Web.PageTitle
+                            Keyword("class"),
+                            WhiteSpace(" "),
+                            Namespace("Microsoft"),
+                            Punctuation("."),
+                            Namespace("AspNetCore"),
+                            Punctuation("."),
+                            Namespace("Components"),
+                            Punctuation("."),
+                            Namespace("Web"),
+                            Punctuation("."),
+                            ClassName("PageTitle")))));
+        });
+    }
+
+    [Fact]
+    public async Task ComponentEndTag_FullyQualified()
+    {
+        TestCode code = """
+            <Microsoft.AspNetCore.Components.Web.PageTitle></Microsoft.AspNetCore.Components.Web.[|Pa$$geTitle|]>
+            <div></div>
+
+            @{
+                var myVariable = "Hello";
+
+                var length = myVariable.Length;
+            }
+            """;
+
+        await VerifyHoverAsync(code, async (hover, document) =>
+        {
+            await hover.VerifyRangeAsync(code.Span, document);
+
+            hover.VerifyRawContent(
+                Container(
+                    Container(
+                        Image,
+                        ClassifiedText( // class Microsoft.AspNetCore.Components.Web.PageTitle
+                            Keyword("class"),
+                            WhiteSpace(" "),
+                            Namespace("Microsoft"),
+                            Punctuation("."),
+                            Namespace("AspNetCore"),
+                            Punctuation("."),
+                            Namespace("Components"),
+                            Punctuation("."),
+                            Namespace("Web"),
+                            Punctuation("."),
+                            ClassName("PageTitle")))));
+        });
+    }
+
+    [Fact]
+    public async Task ComponentEndTag_FullyQualified_Namespace()
+    {
+        TestCode code = """
+            <Microsoft.AspNetCore.Components.Web.PageTitle></Microsoft.[|AspNe$$tCore|].Components.Web.PageTitle>
+            <div></div>
+
+            @{
+                var myVariable = "Hello";
+
+                var length = myVariable.Length;
+            }
+            """;
+
+        await VerifyHoverAsync(code, async (hover, document) =>
+        {
+            await hover.VerifyRangeAsync(code.Span, document);
+
+            hover.VerifyRawContent(
+                Container(
+                    Container(
+                        Image,
+                        ClassifiedText( // namespace Microsoft.AspNetCore
+                            Keyword("namespace"),
+                            WhiteSpace(" "),
+                            Namespace("Microsoft"),
+                            Punctuation("."),
+                            Namespace("AspNetCore")))));
+        });
+    }
+
     private async Task VerifyHoverAsync(TestCode input, Func<Hover, TextDocument, Task> verifyHover)
     {
         var document = CreateProjectAndRazorDocument(input.Text);

src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/Shared/CohostFindAllReferencesEndpointTest.cs

@@ -118,6 +118,38 @@ await VerifyFindAllReferencesAsync(input,
             (FilePath("SurveyPrompt.cs"), surveyPrompt));
     }
 
+    [Fact]
+    public async Task ComponentEndTag_DefinedInCSharp()
+    {
+        TestCode input = """
+            <[|SurveyPrompt|] Title="InputValue"></Surv$$eyPrompt>
+            """;
+
+        // lang=c#-test
+        TestCode surveyPrompt = """
+            using Microsoft.AspNetCore.Components;
+            using Microsoft.AspNetCore.Components.Rendering;
+
+            namespace SomeProject;
+
+            public class [|SurveyPrompt|] : ComponentBase
+            {
+                [Parameter]
+                public string Title { get; set; } = "Hello";
+
+                protected override void BuildRenderTree(RenderTreeBuilder builder)
+                {
+                    builder.OpenElement(0, "div");
+                    builder.AddContent(1, Title + " from a C#-defined component!");
+                    builder.CloseElement();
+                }
+            }
+            """;
+
+        await VerifyFindAllReferencesAsync(input,
+            (FilePath("SurveyPrompt.cs"), surveyPrompt));
+    }
+
     private async Task VerifyFindAllReferencesAsync(TestCode input, params (string fileName, TestCode testCode)[] additionalFiles)
     {
         var document = CreateProjectAndRazorDocument(input.Text, additionalFiles: [.. additionalFiles.Select(f => (f.fileName, f.testCode.Text))]);

src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/Shared/CohostGoToDefinitionEndpointTest.cs

@@ -156,6 +156,38 @@ public async Task Component()
         Assert.Equal(range, location.Range);
     }
 
+    [Fact]
+    public async Task ComponentEndTag()
+    {
+        TestCode input = """
+            <SurveyPrompt Title="InputValue"></Surv$$eyPrompt>
+            """;
+
+        TestCode surveyPrompt = """
+            [||]@namespace SomeProject
+
+            <div></div>
+
+            @code
+            {
+                [Parameter]
+                public string Title { get; set; }
+            }
+            """;
+
+        var result = await GetGoToDefinitionResultAsync(input, RazorFileKind.Component,
+            additionalFiles: (FileName("SurveyPrompt.razor"), surveyPrompt.Text));
+
+        Assert.NotNull(result.Value.Second);
+        var locations = result.Value.Second;
+        var location = Assert.Single(locations);
+
+        Assert.Equal(FileUri("SurveyPrompt.razor"), location.DocumentUri.GetRequiredParsedUri());
+        var text = SourceText.From(surveyPrompt.Text);
+        var range = text.GetRange(surveyPrompt.Span);
+        Assert.Equal(range, location.Range);
+    }
+
     [Fact]
     public async Task ComponentAttribute()
     {