Try adjusting caret position to provide better results from Roslyn

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/AbstractRazorDelegatingEndpoint.cs

@@ -7,6 +7,7 @@
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.LanguageServer.Common;
 using Microsoft.AspNetCore.Razor.LanguageServer.EndpointContracts;
+using Microsoft.AspNetCore.Razor.LanguageServer.Extensions;
 using Microsoft.AspNetCore.Razor.LanguageServer.Protocol;
 using Microsoft.CodeAnalysis.Razor.Workspaces;
 using Microsoft.Extensions.Logging;
@@ -46,6 +47,17 @@ protected AbstractRazorDelegatingEndpoint(
     /// </summary>
     protected virtual bool PreferCSharpOverHtmlIfPossible { get; } = false;
 
+    /// <summary>
+    /// When <see langword="true"/>, we'll adjust the position of the caret to the name portion of an attribute if it is in the
+    /// attribute, but not the name. eg. if we get @bi$$nd-Value we'll act as though we got @bind-$$Value
+    /// </summary>
+    protected virtual bool TreatAnyAttributePositionAsAttributeName { get; } = false;
+
+    /// <summary>
+    /// If <see cref="TreatAnyAttributePositionAsAttributeName "/> is <see langword="true"/>, returns the range of the full attribute
+    /// </summary>
+    protected Range? OriginalAttributeRange { get; private set; }
+
     /// <summary>
     /// The name of the endpoint to delegate to, from <see cref="RazorLanguageServerCustomMessageTargets"/>. This is the
     /// custom endpoint that is sent via <see cref="ClientNotifierServiceBase"/> which returns
@@ -105,7 +117,28 @@ protected virtual Task<TResponse> HandleDelegatedResponseAsync(TResponse delegat
             return default;
         }
 
-        var projection = await _documentMappingService.TryGetProjectionAsync(documentContext, request.Position, requestContext.Logger, cancellationToken).ConfigureAwait(false);
+        var position = request.Position;
+        if (TreatAnyAttributePositionAsAttributeName)
+        {
+            var codeDocument = await documentContext.GetCodeDocumentAsync(cancellationToken).ConfigureAwait(false);
+            var sourceText = await documentContext.GetSourceTextAsync(cancellationToken).ConfigureAwait(false);
+            if (request.Position.TryGetAbsoluteIndex(sourceText, Logger, out var absoluteIndex))
+            {
+                // First, lets see if we should adjust the location to get a better result from C#. For example given <Component @bi|nd-Value="Pants" />
+                // where | is the cursor, we would be unable to map that location to C#. If we pretend the caret was 3 characters to the right though,
+                // in the actual component property name, then the C# server would give us a result, so we fake it.
+                if (RazorSyntaxFacts.TryGetAttributeNameAbsoluteIndex(codeDocument, absoluteIndex, out var attributeNameIndex, out var attributeSpan))
+                {
+                    sourceText.GetLineAndOffset(attributeNameIndex, out var line, out var offset);
+
+                    OriginalAttributeRange = attributeSpan.AsRange(sourceText);
+
+                    position = new Position(line, offset);
+                }
+            }
+        }
+
+        var projection = await _documentMappingService.TryGetProjectionAsync(documentContext, position, requestContext.Logger, cancellationToken).ConfigureAwait(false);
         if (projection is null)
         {
             return default;

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Definition/DefinitionEndpoint.cs

@@ -47,6 +47,8 @@ public DefinitionEndpoint(
 
     protected override bool PreferCSharpOverHtmlIfPossible => true;
 
+    protected override bool TreatAnyAttributePositionAsAttributeName => true;
+
     protected override string CustomMessageTarget => RazorLanguageServerCustomMessageTargets.RazorDefinitionEndpointName;
 
     public RegistrationExtensionResult GetRegistration(VSInternalClientCapabilities clientCapabilities)

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Extensions/TextSpanExtensions.cs

@@ -26,4 +26,7 @@ public static Range AsRange(this TextSpan span, SourceText sourceText)
 
         return range;
     }
+
+    public static Range AsRange(this Language.Syntax.TextSpan span, SourceText sourceText)
+        => new TextSpan(span.Start, span.Length).AsRange(sourceText);
 }

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/FindAllReferences/FindAllReferencesEndpoint.cs

@@ -53,6 +53,8 @@ public RegistrationExtensionResult GetRegistration(VSInternalClientCapabilities
 
     protected override bool PreferCSharpOverHtmlIfPossible => true;
 
+    protected override bool TreatAnyAttributePositionAsAttributeName => true;
+
     protected override Task<IDelegatedParams?> CreateDelegatedParamsAsync(ReferenceParams request, RazorRequestContext requestContext, Projection projection, CancellationToken cancellationToken)
     {
         // HTML doesn't need to do FAR

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Hover/HoverEndpoint.cs

@@ -49,6 +49,8 @@ public RegistrationExtensionResult GetRegistration(VSInternalClientCapabilities
 
     protected override bool PreferCSharpOverHtmlIfPossible => true;
 
+    protected override bool TreatAnyAttributePositionAsAttributeName => true;
+
     protected override string CustomMessageTarget => RazorLanguageServerCustomMessageTargets.RazorHoverEndpointName;
 
     protected override Task<IDelegatedParams?> CreateDelegatedParamsAsync(TextDocumentPositionParams request, RazorRequestContext requestContext, Projection projection, CancellationToken cancellationToken)
@@ -93,7 +95,14 @@ public RegistrationExtensionResult GetRegistration(VSInternalClientCapabilities
         var documentContext = requestContext.GetRequiredDocumentContext();
         var codeDocument = await documentContext.GetCodeDocumentAsync(cancellationToken).ConfigureAwait(false);
 
-        if (_documentMappingService.TryMapFromProjectedDocumentRange(codeDocument.GetCSharpDocument(), response.Range, out var projectedRange))
+        // If we don't include the originally requested position in our response, the client may not show it, so we extend the range to ensure it is in there.
+        // eg for hovering at @bind-Value:af$$ter, we want to show people the hover for the Value property, so Roslyn will return to us the range for just the
+        // portion of the attribute that says "Value".
+        if (OriginalAttributeRange is not null)
+        {
+            response.Range = OriginalAttributeRange;
+        }
+        else if (_documentMappingService.TryMapFromProjectedDocumentRange(codeDocument.GetCSharpDocument(), response.Range, out var projectedRange))
         {
             response.Range = projectedRange;
         }

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Implementation/ImplementationEndpoint.cs

@@ -34,6 +34,10 @@ public ImplementationEndpoint(
 
     protected override string CustomMessageTarget => RazorLanguageServerCustomMessageTargets.RazorImplementationEndpointName;
 
+    protected override bool PreferCSharpOverHtmlIfPossible => true;
+
+    protected override bool TreatAnyAttributePositionAsAttributeName => true;
+
     public RegistrationExtensionResult GetRegistration(VSInternalClientCapabilities clientCapabilities)
     {
         const string ServerCapability = "implementationProvider";

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/RazorSyntaxFacts.cs

@@ -0,0 +1,103 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT license. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.AspNetCore.Razor.Language.Syntax;
+using Microsoft.AspNetCore.Razor.LanguageServer.Extensions;
+
+namespace Microsoft.AspNetCore.Razor.LanguageServer;
+
+internal static class RazorSyntaxFacts
+{
+    /// <summary>
+    /// Given an absolute index positioned in an attribute, finds the absolute index of the part of the
+    /// attribute that represents the attribute name. eg. for @bi$$nd-Value it will find the absolute index
+    /// of "Value"
+    /// </summary>
+    public static bool TryGetAttributeNameAbsoluteIndex(RazorCodeDocument codeDocument, int absoluteIndex, out int attributeNameAbsoluteIndex, out TextSpan fullAttributeNameSpan)
+    {
+        attributeNameAbsoluteIndex = 0;
+        fullAttributeNameSpan = default;
+
+        var tree = codeDocument.GetSyntaxTree();
+        var owner = tree.GetOwner(absoluteIndex);
+
+        var attributeName = owner?.Parent switch
+        {
+            MarkupTagHelperAttributeSyntax att => att.Name,
+            MarkupMinimizedTagHelperAttributeSyntax att => att.Name,
+            MarkupTagHelperDirectiveAttributeSyntax att => att.Name,
+            MarkupMinimizedTagHelperDirectiveAttributeSyntax att => att.Name,
+            _ => null
+        };
+
+        if (attributeName is null)
+        {
+            return false;
+        }
+
+        // Can't get to this point if owner was null, but the compiler doesn't know that
+        Assumes.NotNull(owner);
+
+        fullAttributeNameSpan = GetFullAttributeNameSpan(owner.Parent);
+
+        // The GetOwner method can be surprising, eg. Foo="$$Bar" will return the starting quote of the attribute value,
+        // but its parent is the attribute name. Easy enough to filter that sort of thing out by just requiring
+        // the caret position to be somewhere within the attribute name.
+        if (!fullAttributeNameSpan.Contains(absoluteIndex))
+        {
+            return false;
+        }
+
+        if (attributeName.LiteralTokens is [{ } name])
+        {
+            var attribute = name.Content;
+            if (attribute.StartsWith("bind-"))
+            {
+                attributeNameAbsoluteIndex = attributeName.SpanStart + 5;
+            }
+            else
+            {
+                attributeNameAbsoluteIndex = attributeName.SpanStart;
+            }
+
+            return true;
+        }
+
+        return false;
+    }
+
+    private static TextSpan GetFullAttributeNameSpan(SyntaxNode node)
+    {
+        return node switch
+        {
+            MarkupTagHelperAttributeSyntax att => att.Name.Span,
+            MarkupMinimizedTagHelperAttributeSyntax att => att.Name.Span,
+            MarkupTagHelperDirectiveAttributeSyntax att => CalculateFullSpan(att.Name, att.ParameterName, att.Transition),
+            MarkupMinimizedTagHelperDirectiveAttributeSyntax att => CalculateFullSpan(att.Name, att.ParameterName, att.Transition),
+            _ => Assumed.Unreachable<TextSpan>(),
+        };
+
+        static TextSpan CalculateFullSpan(MarkupTextLiteralSyntax attributeName, MarkupTextLiteralSyntax? parameterName, RazorMetaCodeSyntax? transition)
+        {
+            var start = attributeName.SpanStart;
+            var length = attributeName.Span.Length;
+
+            // The transition is the "@" if its present
+            if (transition is not null)
+            {
+                start -= 1;
+                length += 1;
+            }
+
+            // The parameter is, for example, the ":after" but does not include the colon, so we have to account for it
+            if (parameterName is not null)
+            {
+                length += 1 + parameterName.Span.Length;
+            }
+
+            return new TextSpan(start, length);
+        }
+    }
+}

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Definition/DefinitionEndpointDelegationTest.cs

@@ -99,11 +99,37 @@ public async Task Handle_SingleServer_CSharp_MetadataReference()
         Assert.Equal(21, location.Range.Start.Line);
     }
 
-    [Fact]
-    public async Task Handle_SingleServer_ComponentAttribute_OtherRazorFile()
+    [Theory]
+    [InlineData("$$IncrementCount")]
+    [InlineData("In$$crementCount")]
+    [InlineData("IncrementCount$$")]
+    public async Task Handle_SingleServer_Attribute_SameFile(string method)
     {
-        var input = """
-                <SurveyPrompt @bind-Ti$$tle="InputValue" @bind-Value:after="BindAfter" />
+        var input = $$"""
+                <button @onclick="{{method}}"></div>
+
+                @code
+                {
+                    void [|IncrementCount|]()
+                    {
+                    }
+                }
+                """;
+
+        await VerifyCSharpGoToDefinitionAsync(input, "test.razor");
+    }
+
+    [Theory]
+    [InlineData("Ti$$tle")]
+    [InlineData("$$@bind-Title")]
+    [InlineData("@$$bind-Title")]
+    [InlineData("@bi$$nd-Title")]
+    [InlineData("@bind$$-Title")]
+    [InlineData("@bind-Ti$$tle")]
+    public async Task Handle_SingleServer_ComponentAttribute_OtherRazorFile(string attribute)
+    {
+        var input = $$"""
+                <SurveyPrompt {{attribute}}="InputValue" />
 
                 @code
                 {
@@ -158,12 +184,12 @@ @namespace BlazorServer_31.Shared
         Assert.Equal(range.Start.Character, location.Range.Start.Character);
     }
 
-    private async Task VerifyCSharpGoToDefinitionAsync(string input)
+    private async Task VerifyCSharpGoToDefinitionAsync(string input, string filePath = null)
     {
         // Arrange
         TestFileMarkupParser.GetPositionAndSpan(input, out var output, out var cursorPosition, out var expectedSpan);
 
-        var codeDocument = CreateCodeDocument(output);
+        var codeDocument = CreateCodeDocument(output, filePath: filePath);
         var razorFilePath = "C:/path/to/file.razor";
 
         // Act